Ethiopian, Lion Air, and the 737 MAX

Ethiopian Airlines CEO Tewolde Gebremariam at the 737 crash site.


UPDATE: May 20, 2019

The 737 MAX saga is spinning in so many different directions now that I’ve decided to lay off the updates for a while. The media, both big and small, have been doing a surprisingly good job with this story — and all of its various substories — and at this point there’s little that I can add, from the perspective of an airline pilot or insider, that I haven’t already said in the installments below.


UPDATE: April 13, 2019

What a mess. Boeing is getting knocked around by everyone from members of Congress to late-night comedians. The MAX’s certification program is under scrutiny, airlines are canceling orders, and passengers everywhere are scared. The FAA is facing accusations that it took far too long to order the MAX’s grounding (after numerous other countries had already done so), and that it basically permitted Boeing to self-certify an unsafe aircraft.

We keep hearing, too, about what a horrible black mark this is not merely against Boeing, but against American aviation’s place in the world. We are no longer the global leader in air safety, no longer the “gold standard,” whatever that means exactly, as several articles have described it. This is maybe just another example of the weird phenomenon known as American exceptionalism, but each time I hear it, I keep going back to the DC-10 fiasco in the 1970s.

In 1974, in one of the most horrific air disasters of all time, a THY (Turkish Airlines) DC-10 crashed after takeoff from Orly Airport outside Paris, killing 346 people. The accident was traced to a faulty cargo door design. (The same door had nearly caused the crash of an American Airlines DC-10 two years earlier.) McDonnell Douglas had hurriedly designed a plane with a door that it knew was defective; then, in the aftermath of Paris, tried to cover the whole thing up. It was reckless, even criminal. Then, in 1979, American flight 191, also a DC-10, went down at Chicago-O’Hare, killing 273 — to this day the deadliest air crash ever on U.S. soil — after an engine detached on takeoff. Investigators blamed improper maintenance procedures (including use of a forklift to raise the engine and its pylon), and then found pylon cracks in at least six other DC-10s, causing the entire fleet to be grounded for 37 days. The NTSB also cited design flaws in the engine pylon and wing slats, quality control problems at McDonnell Douglas, and “deficiencies in the surveillance and reporting procedures of the FAA.”

That’s two of history’s ten deadliest air crashes, complete with design defects, a cover-up, and 619 dead people. And don’t forget the 737 itself has a checkered past, going back to the rudder problems that caused the crash of USAir flight 427 in 1994 (and likely the crash of United flight 585 in 1991). Yet the DC-10, the 737, and America’s aviation prestige along with them, have persevered. If we survived the those scandals we can probably manage this. I have a feeling that a year from now this saga will be mostly forgotten. Boeing and its stock price will recover, the MAX will be up and flying again, and on and on we go. This is how it happens.

There’s also a lot being made of the FAA’s more or less outsourcing aircraft certification to Boeing. This is frustrating, and ironic, because air travel has never been safer, and it’s partly because, not in spite of, the close relationship and collaborative efforts between regulators, airlines, manufacturers, pilot groups, and so on. (A good example is the self-reporting program between pilots and FAA, which has been very successful and has kept dangerous trends from being driven underground.) Bear in mind how much these parties stand to lose should a tragedy occur. A crash can destroy an airline outright. It’s in the interest of all these entities to play things as safely as possible.

Did something go wrong in the 737 program? Are Boeing and the FAA jointly responsible? Probably. But I don’t believe anybody was intentionally reckless. That’s an important distinction, and for the most part the relationships between industry and regulators has been a productive one. You can’t say that about banking, perhaps, but in aviation it seems to work. The remarkable safety record we’ve enjoyed over the past twenty years bears that out, absolutely.

For the airline passenger, these can seem like scary times. Air crashes, perhaps more than any other type of catastrophe, have a way of haunting the public’s consciousness, particularly when the causes are mysterious. My best advice, maybe, is to turn off the news, take a step back, and try to look at this through a wider lens. The fact is, Lion Air and Ethiopian notwithstanding, air travel has never been safer than it is today. Two fatal crashes in five months is tragic, but in decades past it wasn’t unusual to see ten, fifteen, or even twenty air disasters worldwide in a given year. Nowadays, two or more is downright unusual. Here in the United States there hasn’t been a large-scale fatal crash involving a mainline carrier in nearly twenty years — an absolutely astonishing statistic. There are far more planes, carrying far more passengers, than ever before, yet the accident rate is a fraction of what it once was.

I have a question, however:

One of the things I can’t help wondering about is why the 737 MAX needed to exist in the first damn place. Somewhere deep down, perhaps the heart of this whole fiasco is stubbornness — that is, Boeing’s determination to keep the 737 line going, variant after variant, seemingly forever. Instead of starting from scratch with a new airframe, they took what was essentially conceived as a regional jet in the mid-1960s, and have pushed and pushed and pushed the thing — bigger and bigger engines, fancier avionics and more seats — into roles it was never intended for.

For a jet of its size, it uses huge amounts of runway and has startlingly high takeoff and landing speeds. The passenger cabin is skinny and uncomfortable; the cockpit is incredibly cramped and noisy. I don’t care how many changes and updates the plane has undergone; at heart, it’s still a blasted 737 — a fifty year-old design trying to pass itself off as a modern jetliner. The “Frankenplane,” I call it. Look at that tell-tale nose and windscreen. Do you recognize that? It’s the 707, from 1958, unchanged.

I’m not saying this is the reason, directly, for what happened in Indonesia or Ethiopia, but is it maybe not time, at last, to move on from the 737 platform?


UPDATE: April 6, 2019

This just makes you shake your head.

What seems to be the case, based on analysis of the voice and data recorders from the doomed Ethiopian Airlines flight 302, is that the pilots did, as they should have, engage the plane’s pitch trim disconnect switches in a frantic attempt to regain control after a malfunctioning MCAS system forced the plane’s nose toward the ground. This pair of switches, on the center console near the thrust levers, killed power to the entire automatic pitch trim system, including MCAS, and should have allowed the pilots to maintain a normal flightpath using manual trim and elevator. Manual trim is applied by turning a large wheel mounted to the side of that same center console. Elevator is controlled by moving the control column forward or aft.

Yet they did not, could not, regain control. The reason, many now believe, is a design quirk of the 737 — an idiosyncrasy that reveals itself in only the rarest of circumstances, and that few 737 pilots are aware of. When the plane’s stabilizers are acting to push the nose down, and the control column is simultaneously pulled aft, a sort of aerodynamic lockout forms: airflow forces on the stabilizers effectively paralyze them, making them impossible to move manually.

Aboard flight 302, the scenario goes like this: Commands of the faulty MCAS are causing the automatic trim system to push the nose down. The pilots, trying to arrest this descent, are pulling aft on the control column. Thus setting up this scenario perfectly. The trim forces are stronger than the control column forces, which is why pulling back on the column has no effect. But now, with power to the trim system shut off, they can lift the nose by manually by rotating the trim wheel aft, relieving that unwanted nose-down push. But the wheel won’t move. Believing the manual trim is itself broken, the pilots then reengaged the auto-trim. MCAS then kicks in again, pushing the nose down even further. What’s worse, as the plane’s speed increases, the lockout effect intensifies. And so with every passing second it becomes more and more difficult to recover.

The correct course of action would be to relax pressure on the control column, perhaps to the point of pushing the nose down even further. This will free the stabilizers of the aerodynamic weirdness that is paralyzing them, and allow the trim wheel to move, realigning the stabilizers to a proper and safe position. For the pilots, though, such a move would be completely counterintuitive. Instead, they do what any pilots would be expected to do under the circumstances. Turns out it’s the wrong thing, but really they have no way of knowing.

It’s possible, or probable, that the pilots of Lion Air flight 610 faced exactly the same situation, with the same result.

Apparently, pilots of older-generation 737s — long before there was MCAS — were aware of the lockout potential, and some were trained accordingly. (I flew the “classic” 737-200, briefly, about twenty years ago, but have no memory of it one way or the other.) However, as an obscure phenomenon that no pilot was likely to ever encounter, it was eventually forgotten as the 737 line evolved, to the point where no mention of it appears in the manuals of later variants.

Circles, left to right:

1. Electric trim switches. With the autopilot engaged the pitch trim system operates automatically. With the autopilot off, the pilot controls the trim by manipulating these switches forward or aft, usually with his or her thumb.

2. Trim wheel. This is the wheel that the pilot will rotate forward or aft to control trim manually.

3. The disconnect switches. These kill power to the trim system. Auto-trim and the thumb switches are now shut off; trim is adjusted using the wheel in the second circle.


UPDATE: March 29, 2019

ON MARCH 10th, Ethiopian Airlines flight ET302, a Boeing 737 MAX bound for Nairobi, crashed after takeoff from Addis Ababa, killing 157 people from more than thirty countries. Five months earlier, 189 people perished after Lion Air flight JT610 went down near Jakarta, Indonesia, under eerily similar circumstances. Both planes were brand new 737 MAX jets. Both crashed shortly after takeoff following a loss of control.

Although findings from the voice and data recorders pulled from the Ethiopian wreckage haven’t been released yet, it’s all but assumed that flight succumbed to the same flight control malfunction that brought down Lion Air. The 737 MAX has a deadly design problem, and Boeing needs to fix it. In the meantime, all MAX jets remain grounded worldwide.

The culprit is something called MCAS, which stands for Maneuvering Characteristics Augmentation System, a system that adjusts control feel as the plane’s nose pitches upward, effectively nudging it downward.

MCAS operates in the background, transparently and automatically — there’s no on or off switch, per se — and only during a very narrow window of the jet’s flight envelope. This is not something that occurs in normal, day-to-day operation, but certification requires it for those occasions when, for whatever reason, the plane reaches unusually steep climb angles. To raise a plane’s nose, the pilot pulls back on the control column. As the nose pitches further and further upward, the control forces required to maintain this action are supposed to become heavier. This helps keep pilots, and/or the autopilot, from inadvertently stalling the plane — that is, exceeding what we call the “critical angle of attack,” at which point the wings run out of lift and the plane ceases to fly. On the 737 MAX, however, certain aerodynamic factors, including the placement of its very powerful engines, result in control forces actually becoming lighter as it approaches the point of stall. Because of this the plane would not meet certification standards. And so MCAS was engineered in to properly adjust the feel.

Thus there’s a certain beauty to MCAS — provided it works correctly. What’s happening, apparently, is that faulty data is being fed to MCAS by the plane’s angle of attack indicator — a small, wedge-shaped sensor near the plane’s nose that helps warn pilots of an encroaching aerodynamic stall. An impending stall is sensed when there isn’t one, triggering the plane’s stabilizer trim — stabilizers are the wing-like horizontal surfaces beneath the tail — to force the nose down. This sets up a battle of sorts between the pilots and the trim system until the plane becomes uncontrollable and crashes.

What leaves us stymied, though, is the fact that any MCAS commands, faulty or not, can be overridden quickly through a pair of disconnect switches. Why the Lion Air pilots failed to engage these switches is unclear, but unaware of the system’s defect in the first place, we can easily envision a scenario in which they became overwhelmed, unable to figure out in time what the plane was doing and how to correct it. From that point forward, however, things were different. “Though it appears there’s a design flaw that Boeing will need to fix as soon as possible,” I wrote in November,“passengers can take comfort in knowing that every MAX pilot is now acutely aware of this potential problem, and is prepared deal with it.”

Or so it seemed. With the Lion Air crash fresh on any MAX pilot’s mind, why did the Ethiopian pilots not immediately disconnect the trim system? Did a disconnect somehow not work? Was the crew so inundated by a cascade of alarms, warnings, and erratic aircraft behavior that they failed to recognize what was happening? Or, was the problem something else completely? This is the most perplexing part of this whole unfolding drama.

While we wait for the black box results, Boeing this week revealed a suite of hardware and software tweaks that it claims will rectify the issue. This includes incorporation of a second angle of attack indicator, and an alerting system to warn pilots of a disagreement between the two.

Ethiopian Airlines 737 MAX

The largest MAX operators in the U.S. are American Airlines, Southwest and United. Other customers include Alaska Airlines, Air China, Norwegian, FlyDubai, China Eastern and China Southern. The type is most easily recognize by its 787-style scalloped engine nacelles, which earlier 737s do not have.

Founded in 1945, Ethiopian Airlines is the largest carrier in Africa. Westerners hear “Ethiopia” and tend to make certain, unfortunate associations, but this is company with a proud history and a very good safety record. It flies a state-of-the art fleet, including the Boeing 787 and A350, on routes across four continents. Its training department, the Ethiopian Airlines Aviation Academy, has been training pilots for 55 years. Ethiopian’s pilots are distinguished by their handsome, olive green uniforms.

The captain of the doomed flight ET302, Yared Getachew, was a graduate of the highly competitive Ethiopian Airlines Aviation Academy, and had more than 8,000 flight hours — a respectable total. “Yared was a great person and a great pilot. Well prepared,” a former Ethiopian Airlines training captain told me.

The first officer, on the other hand, had a mere two-hundred hours. Airline training is intensive, and as I’ve written in the past, the raw number of hours in a pilot’s logbook isn’t always a good indicator of skill or talent. Nonetheless, if indeed that number is correct (it’s unclear if this refers to his total flight time, or his number of hours in the 737 MAX), that’s pretty astounding. By comparison, the typical new-hire at a U.S. major carrier has somewhere on the order of 5,000 hours. Whether the first officer’s lack of experience had anything to do with the accident, however, is another matter.


Cockpit photo by Vedant Agarwal, New York Times
Thumbnail photo by Michael Toweled, AFP

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329 Responses to “Ethiopian, Lion Air, and the 737 MAX”
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  1. Rod says:

    The “International Airlines Group” has apparently just ordered 200 MAXs. (They lease to Vueling among others, so don’t laugh.)

    What do you think? Five cents a piece?

  2. Thomas says:

    Have you watched this documentary on the 787?


    Yes, I just finished watching it. Very troubling.

    There were so many individuals saying that fasteners were not installed properly, that it is amazing that a 787 structural failure has not occurred.

    The government should impound a 787 and take the airplane apart, to test the whistle-blowers’ accusations of faulty assembly. This would either provide needed evidence, or exculpate Boeing.

    • Rod says:

      Sure, Thomas, I’ve watched it. Have you seen who (or What) has been nominated to head the FAA?

      So I don’t see any such radical step being taken. And I suppose even a D-check wouldn’t go that deep.

      Perhaps all will be well because somehow it just won’t matter. Or perhaps these things are flying time bombs like the Comet and the Electra: one fine day BOOM. And it could all start happening sort of at once.
      Or not at all.

      What grabbed my attention was that 32-year-veteran Boeing aeronautical engineer admitting she had been avoiding flying on the 787.
      (Everett or Charleston? Flip a coin.)

  3. Thomas says:


    The following statement is embedded in the article referenced below:
    “The Max wasn’t handling well when nearing stalls at low speeds.”

    • Rod says:

      Thanks, Thomas.
      Meaning, I guess, that a wing was dropping or some other ominous event.
      This article really shows the confusion that reigned among Boeing staff about what was, and wasn’t, going into the airplane.

      “Expanding the use of MCAS to lower-speed situations required removing the G-force threshold. MCAS now needed to work at low speeds so G-force didn’t apply.” Greek to me.

      “The change meant that a single angle-of-attack sensor was the lone guard against a misfire. Although modern 737 jets have two angle-of-attack sensors, the final version of MCAS took data from just one.” But there was no Technical reason to have only one, right? Boeing did this to lower the price and sell more planes, correct?

      Yes, no matter how you add this up, Boeing was negligent and the FAA was whistling Dixie.

      Have you watched this documentary on the 787?

      It illustrates the mindset that led to Mad Max.

      • Thomas says:

        “Expanding the use of MCAS to lower-speed situations required removing the G-force threshold. MCAS now needed to work at low speeds so G-force didn’t apply.” Greek to me.

        When you get on an elevator, and it start to move up rapidly, you can feel the G-force, as your body is pressed down, against the elevator floor.

        If you bank the wings sharply, and pull a very tight, high-speed turn, while keeping the airplane level, then you are pulling a lot of G-force (pressing your body against the airplane seat), at a high angle-of-attack. If the wing stalls at this high bank-angle, it can be disastrous, in trying to control the airplane. So, with a G-force threshold, they were not going to let MCAS take action, even with a high angle-of-attack, unless the bank-angle of the wing, and the speed of the airplane, was great enough. This was the original version of MCAS.

        At lower speeds, you would generate a lower G-force, and they wanted MCAS to work at low speeds, so they had to remove the G-force threshold.

      • Thomas says:

        “The change meant that a single angle-of-attack sensor was the lone guard against a misfire. Although modern 737 jets have two angle-of-attack sensors, the final version of MCAS took data from just one.” But there was no Technical reason to have only one, right? Boeing did this to lower the price and sell more planes, correct?

        No, incorrect. There have always been two angle-of-attack sensors on the MAX, but to make the software simpler to develop, they only took data from only one of the sensors. The software would have been more complex, to examine the inputs from both sensors, to determine if MCAS should change the pitch of the airplane. So, recklessly, they ignored the angle-of-attack being reported by one of the sensors.

        I have not watched the 787 documentary which you referenced. I’m starting to watch it now.

        • Rod says:

          Thanks. I realize that at high bank angles (which diminish the vertical component of lift) you’d better increase the AoA and engine thrust to overcome the resulting drag. At low speeds you’re basically closer to the stall anyway (hence flaps, slats, whatever). Sure, a 60° bank induces 2 Gs I seem to remember. I just didn’t understand what they meant by “the G-force threshold”, and doubt your average NYT reader will either.
          (I remember slow-speed training as a student pilot … you were a hairsbeadth from the stall and supposed to be keeping it that way while your instructor ranted about the price of apples these days to distract you.)

          “Recklessly, they ignored the angle-of-attack being reported by one of the sensors.”

          Well, let’s hope they’ll have to answer for that in court. It’s a rather incredible irony that Ralph Nader’s grand-niece was aboard the Addis flight. I’m sure that particular news didn’t make Boeing management’s day.

  4. Thomas says:

    Rod, you are right about the Amsterdam 737 crash.

    I had to look-up Turkish 1951, but I remember it now. I couldn’t remember the answer to any of your three questions.

    Those pilots were just along for the ride. Reminds me of Asiana 214.

  5. Thomas says:

    “Flawed: Why the Boeing 737 Max Should Be Permanently Grounded”

    • Rod says:

      Good piece. Was away from the internet for 10 days in May, and when I got back, this article had disappeared from the ‘front page’, yet the debate about Boeing was going great guns on the Chicago-crash thread. So it never occurred to me to look at this article again.

      It isn’t — from what I can see — just the much-derided mainline media that won’t let this story go, but aviation community itself. However, I think Patrick would tell you the DC-10 was also a flawed airplane, but managed to end its career without Too much trouble. So I guess Boeing will now apply the best bandaid it can devise, and bet the company on that.

      People WILL forget. Remember that 737 that crashed in Amsterdam about 10 years ago? Remember the airline? The cause? Lotta people killed? I’ll admit that third one has me stumped. And I had to think for a minute about the second one. See what I mean?

      And the latest is that Boeing is seeking to rebrand the thing. I could suggest “Mad Max”. (MAD = Mutant Antistall Diceroll.) But seriously, if the proposed patch had been installed in the original aircraft and Boeing had been upfront about everything, we wouldn’t be sitting here talking about all this. Of course it’s a scandal that they ever pushed the 737 so far, and did the whole thing in such a grasping, negligent way. But the ultimate question is whether they can offer something that won’t crash and that will make money for their customers. If not, they’re crazy to persist.

      • Thomas says:

        This is why I said in the other stream, that they are sweeping the stall-proclivity under the rug.

        So, they neutered MCAS, and it may trigger once, or not at all. The underlying stall-proclivity can still take down the MAX.

        I read in one of the articles that the MAX has very poor low-speed stall handling characteristics. So, whether MCAS triggers once, or not at all may be inconsequential. A low-speed stall may not be recoverable, except by the most-skilled pilots. The article didn’t say how catastrophic the low-speed stall was. If it brings down another MAX, think of the number of lawsuits, and the dollar-magnitude. Think bankruptcy.

        And, there’s still the issue of runaway-trim below 10000′ AGL. With 1300+ NGs, it’s not hard to generate 750,000 flights. I figure, maybe 144 days, but I haven’t been able to find out how many flights per day an NG is used for, so I conservatively assumed 4. So, the runaway-trim on an NG/MAX will generate a heap of lawsuits, and probably bankruptcy.

        If they do not retrofit a second (redundant) trim-motor on the NG, I think that I will steer-clear of the NG, as well as the MAX. It will be somewhat difficult to get from point-to-point by air, with these restrictions.

        I can try to find the article referenced above, if you desire to read about the low-speed stall issue. I’m not sure if I bookmarked it.

        • Rod says:

          Here’s a question (and again, based merely on something I read…), if it’s low-speed stalls that are the biggest danger in the MAX, why on EARTH did they have an MCAS that activates only when the gear retracts (and presumably deactivates when it’s extended)? I think I got that info from those Monday-morning quarterbacks after Addis who said “If it had been me with a stick-shaker at take-off, I wouldn’t have retracted the gear.”(?)

          Well, we’ll see about the NG. I live in Europe, and you sure don’t see a whole lot of them here. (That’s not counting the ubiquitous Ryanair.) KLM’s got ’em, indeed the King of the Netherlands is type-rated. (Now THAT would put the hurt on Boeing….)

          Yes, I’d be grateful for any link, though I know how these things go astray.

          • Thomas says:

            I’ll get to the landing gear next.

            MCAS is disabled when the flaps and slats are extended to any setting, and enabled when the flaps and slats are retracted.

            Some airplanes pitch-up when the flaps are retracted, and some airplanes pitch-down when the flaps are retracted. It has to do with the change in the center-of-lift, when the wing changes shape, as the flaps are retracted.

            I assume that the MAX pitches-up when the flaps are retracted, since that would move the nose in the direction of a stall, and would suggest enabling MCAS to prevent any such developing stall. When the flaps are extended, I assume the nose would pitch-down on the MAX, reducing the chances of a stall — so MCAS is disabled with a flap extension.

            Under normal circumstances, the flaps will be extended, when the landing gear is extended. That is why MCAS is disabled on takeoff, with the landing gear extended.

            If a hydraulic failure occurred, and the airplane shoots a no-flaps approach and landing, I don’t know if MCAS would remain enabled, when they dropped the gear.

            I’m still searching for the low-speed stall article.

  6. KC Toh says:

    The Lion and Ethiopian flights were in no danger of stalling. MCAS, relying on faulty sensor data felt they were stalling. Stalling is when plane continues to lose airspeed too be able to fly aerodynamically. Apart from AoA data, MCAS, like the pilots, would be aware of other data like airspeed, pitch, and rate of climb. Airspeed: 400 mph. Planes don’t stall at 400. Under MCAS, pitch: downwards. Airspeed would increase. Rate of climb: negative, stalls take place when positive. So MCAS forced plane to dive when it was not about to stall.
    So Boeing is modifying MCAS so it would rely on both sensors. If both sensors fail MCAS would be allowed to crash the planes again?
    How about relying on other data? How about letting pilots override?

  7. Thomas says:


    The article below suggests that Boeing changed the STAB TRIM CUT-OUT switches for the MAX from the 737 NG.

    This is a bit complicated, but:
    If Boeing had left the switches unchanged, then Ethiopian 302 might possibly have re-energized the left STAB TRIM CUT-OUT switch, and NOT RE-ENERGIZED the right STAB TRIM CUT-OUT switch. This would have provided electric trim-capability via the yoke-column, WITHOUT RE-ACTIVATING MCAS.

    When Ethiopian 302 couldn’t turn the manual trim-wheel they might possibly have re-energized the left STAB TRIM CUT-OUT switch, and used electric
    trim-capability to re-trim the stabilizer. This might have saved the airplane from diving into the ground.

  8. Werner says:

    I am a layperson wondering: If Boeing needed more space underneath the wings of the 737 to fit the new engines why not add that space by extending the length of the landing gear. Wouldn’t it have been easier to add say 30 or 40cm to the length of the landing gear and leave the new engines in exact the same position the old one were in, instead of disturbing basic flight characteristics by moving the engines forward to gain that space?

    • Rod says:

      Apparently this was not feasible. Exactly why I don’t know.

      • PD says:

        Hi Rod, apparently a longer landing gear would have meant modifying the fuselage for retraction, as some articles have saud.

        • Rod says:

          Hi PD. As Peter Garrison has pointed out, the 737 was designed in the ’60s as a low rider so it could easily carry it’s own deployable airstairs in a world where airport infrastructure was literally thin on the ground.

          In the long-since-changed environment of today, this — like so many other aspects of the 737 — is laughably out of date.

          But then it seems that some cockpit mechanisms on the MD-90 are down to the last molecule identical to those used on the DC-3 …

    • Thomas says:

      That would entail a total redesign of the wing root, which will widen the wingspan, change the center of lift and necessitate a fuselage change to compensate for the change in center of gravity. The nose section would also need to be stretched for the longer nose gear.

      The aerodynamics and fuel efficiency would change as well, not for the better.

      And after all that, a complete re-certification of the airplane.

      [ From ]

  9. PD says:

    The entire focus naturally is on MCAS but I’m sure the probe will have recommendations for a situation where the stabliser gets locked in its extreme position. I don’t know if I remember correctly, in the case of AF 447, a retired pilot had suggested disabling auto trim in alternate law.

    • Thomas says:

      If MCAS had a second, independent trim-motor, then MCAS could be disabled, while still having electric-trim capability.

    • Thomas says:

      WHAT A MESS.

      The article below suggests that Boeing changed the STAB TRIM CUT-OUT switches for the MAX from the 737 NG.

      This is a bit complicated, but:
      If Boeing had left the switches unchanged, then Ethiopian 302 might possibly have re-energized the left STAB TRIM CUT-OUT switch, and NOT RE-ENERGIZED the right STAB TRIM CUT-OUT switch. This would have provided electric trim-capability via the yoke-column, WITHOUT RE-ACTIVATING MCAS.

      When Ethiopian 302 couldn’t turn the manual trim-wheel they might possibly have re-energized the left STAB TRIM CUT-OUT switch, and used electric
      trim-capability to re-trim the stabilizer. This might have saved the airplane from diving into the ground.

  10. Rod says:

    “The planemaker said it had intended to provide the feature as standard, but did not realise until deliveries had begun that it was only available if airlines purchased an optional indicator.”

    TRANSLATION: I didn’t know it was loaded!

  11. Mark says:

    When will this thing be over? The Times Union reporting of a military charter crash included this reference to the MAX: “The plane is a different model of Boeing 737 than the type that was recently grounded worldwide following two deadly crashes.”

    This crash looks like a combination of bad weather and inexperienced flight crew, but we’ll see. The airport had another incident 6 years ago.

    I remember a crash at Logan on 1982 when a plane skidded off icy conditions and ended up with the front of the plane including the cockpit ripped off and into Boston harbor. 2 passengers were never found, presumed drowned.

    • Rod says:

      Well, this is the thing. When will it be over? Assuming the MAX makes it back into the air, people will still be Afraid of it. And if Any MAX crashes for ANY reason, all that fear will come rushing straight back.

      Boeing’s customers must be furious. I was booking with Air Canada the other day and couldn’t get anywhere with their website. So I called them up, and found that the agent’s info in some points directly contradicted the site’s (date of non-stop, type of aircraft). She said “It’s the MAX grounding. Things have been chaotic here for weeks.” Apparently if you fly from, say, Winnipeg to Saskatoon at the moment, don’t be too surprised to find yourself on board a wet-leased Oman Air plane.

      Boeing is wayyyy deep in the Doghouse.

      • Patrick says:

        Again, remember the DC-10. There were horrible accidents, the plane was grounded, a scandal ensued. And when the grounding was lifted… people got on board. Some passengers were nervous, sure, but there was no bottom-line impact for the airlines. And soon enough the whole thing was more or less forgotten. It will happen this way with the MAX also.

        American took the “DC-10 Luxury Liner” decals off their planes and replaced them with “American Airlines Luxury Liner.”

  12. Rod says:

    THOMAS: “On the MAX, the engine nacelles actually develop lift at high angles of attack. So, when the nose starts to pitch-up from the application of power, the nacelles start to experience a high angle-of-attack, which adds even more lift, and pitches up the nose even more, because the nacelle-lift is forward of the center-of-left of the wings. This is what makes the MAX such an unsafe aircraft.”

    Whoa! Vicious circle. Well surely they can redesign the freaking nacelles. There must be a way to do away with their lift-happy nature.

    At all events, it sounds like Boeing went and broke the 737 but good, so they had to fix it, but did this in a hurry and on the cheap, thus killing hundreds of people and leaving their reputation in tatters.

    Rather than thrash around for a better Fix, I wonder if it would be conceivable at this point for them to say “Look, let’s forget the whole thing. We’ll scrap the whole project, reimburse and compensate our furious customers and design a brand-new aircraft at a Nice Price, to regain your confidence. Full accountability here.”

    I doubt they could afford that financially. Which will oblige them to stick with the MAX.

    That said, a Boeing/Airbus duopoly has got to be better than an Airbus monopoly.

    • Thomas says:

      You are exactly correct.

      The responsible thing to do was abandon the Engineering Development of the MAX variant, when the stall-proclivity was determined.

      Now, they are invested even deeper, and need to rescue the project with MCAS. They can’t write-off BILLIONS of dollars, and throw in the towel now on the MAX. But cancelling the MAX, is the responsible thing to do now.

      So, there’s four future outcomes:
      1) They fix MCAS with 100% reliability, and there’s never another MCAS issue, nor stall issue, nor runaway-trim issue
      2) MCAS doesn’t activate when required, the airplane stalls, and another 190 souls perish
      3) MCAS triggers erroneously again, there is a runaway-trim issue, the roller-coaster recovery technique fails, and another 190 souls perish
      4) (2) or (3) above occurs, except the airplane is saved, but pilots become so afraid of the airplane, they refuse to fly it further

      For Boeing, it’s a good bet – risk another 190 souls to preserve BILLIONS in profits. For me, it’s too unsafe an aircraft to risk my life, and I won’t ride on any MAX flight. My goal is to present these facts – so that anyone can make their own decision about riding on a MAX flight.

      If another 190 souls perish, there should be no mercy for those deemed culpable.

  13. Gottettaz says:

    The latest from The Onion: “Five things to know about Boeing’s ongoing issues”

    • Rod says:

      Yeah, that last “joke” is a very serious point. The path that leads Boeing out of the doghouse is a mighty long and uncertain one.

  14. Rod says:

    Thomas: We ran out of space. No more “Reply”.

    “The trim wheel will not turn because the jack-screw for the stabilizer will not turn. The air pressure on the elevator is forcing the stabilizer in the direction opposite of that which the jack-screw is trying to move it.”

    1) In OTHER words, the feeble power (even hydraulic-boosted)available to a trim wheel is nothing against that pressure.

    2) And the ironic thing is that back elevator Exacerbates it because it actually removes some of the air pressure that would otherwise help the jackscrew move things back.

    “You’d better hope that the bottom of the roller-coaster is > 0′ AG (…)”

    Sure, that’s one reason the Ethiopians were screwed: they were flying toward rising terrain, which meant they were running out of Think-Fast room very quickly.

    Apparently the 707 “roller coaster” I heard about was executed at low altitude above downtown Toronto. Doan bear thinkin’ about, do it?

    “Does MCAS cause more safety issues than it solves?”

    If the effing thing worked properly, it would. But it doesn’t.
    What you’re Really asking is: If things are so overstretched and misconceived that you need all these fancy bandaids to keep what used to be a nice, safe airplane out of stall territory, MAYBE you should stop whipping a dead horse and go back to Square One (pardon mixed metaphors).

    (outta space … again)

    • Rod says:

      “Once the stall-proclivity of the MAX was observed, should the design of the variant model have been abandoned ?”

      They were sprinting against the A320neo: they needed something instantly, cheap (one AOA, no extra training, etc.) and familiar.

      Whereas abandoning the 737 would have Cost Billions and Taken Years. I’m not defending them, but that clearly was what motivated them.

      What burns me up is the FAA. Its job is to REGULATE Boss Hogg, not be pals with him.

      • Thomas says:

        2) And the ironic thing is that back elevator Exacerbates it because it actually removes some of the air pressure that would otherwise help the jackscrew move things back.

        No, incorrect. Air pressure from up-elevator will be trying to push the leading-edge of the stabilizer upward. The jack-screw is trying to push the leading edge of the stabilizer downward, to achieve up-trim of the stabilizer (nose-up). The jack-screw can’t turn because of this pressure from the elevator. If they installed a monster hydraulic pump to drive the jack-screw, I do not know if the stabilizer material would fail, because of the tremendous opposing forces.

        I apologize, in advance, for the following facetious statement:
        Since MCAS will be along for the ride, why not put it to good use. Just load 20% more cargo into the rear hold. So what, if the airplane is a little tail-heavy. If they unintentionally got a bit slow on the airspeed, and the nose began to pitch up, because of the tail-heaviness, MCAS would have their back. MCAS would kick-in to push the nose over, while they added power to restore the airspeed.

        So, would you want to be flying around in a tail-heavy airplane, because they engineered-in MCAS to solve the problem ? Well, I’m not sure I want to be flying around in an airplane with a proclivity to stall, because they engineered-in MCAS to solve the problem.

        • Rod says:

          Thanks. Somebody finally answers my longstanding question.
          So actually the “roller coaster” method consists in Somehow avoiding a fatal overspeed and Somehow being in a position to have at least neutral, if not preferably down, stabilizer (at tolerably low airspeed) while the other pilot cranks like crazy. Correct?

          The thing with the MAX though — as I understand it — is that these new mega-engines had to be placed so far forward that thrust application could all too easily take you into stall territory (compared with previous 737s), so the blasted thing automatically has a proclivity to stall, and MCAS was necessary as the bandaid for that proclivity.

          Now they’re devising a New, Bigger, Extra-Special bandaid. And their reputation — with the public generally and with a range of hopping-mad airlines — lies in tatters.

          Talk about false economies.

          • Rod says:

            Oh Lord, these uneditable posts. I meant Down ELEVATOR.

          • Thomas says:

            So actually the “roller coaster” method consists in Somehow avoiding a fatal overspeed and Somehow being in a position to have at least neutral, if not preferably down, stabilizer (at tolerably low airspeed) while the other pilot cranks like crazy. Correct?

            Correct. Neutral elevator will alleviate the adverse pressure on the jack-screw, and the trim-wheel can be used to up-trim the stabilizer, and raise the nose of the airplane, because the jack-screw will now turn. Once you have neutral-elevator, the speed will have probably increased, since the airplane will have been diving while the stabilizer was down-trimmed (nose-down). Pulling the power back to 60% – 70% N1, probably would result in a reasonable speed.

            On the MAX, the engine nacelles actually develop lift at high angles of attack. So, when the nose starts to pitch-up from the application of power, the nacelles start to experience a high angle-of-attack, which adds even more lift, and pitches up the nose even more, because the nacelle-lift is forward of the center-of-left of the wings. This is what makes the MAX such an unsafe aircraft.

            “…is that these new mega-engines had to be placed so far forward that thrust application could all too easily take you into stall territory…”
            Absolutely correct. Rapid power application causes the nose to pitch-up, which cascades into nacelle-lift, which causes the nose to pitch-up even more, which, as you say, can “all too easily take you into stall territory.”

  15. Thomas says:


    If the 737 MAX can be overpowered into a stall, is it inherently unsafe, even if the MCAS engages successfully ?

    If the MCAS activates erroneously again, is the 737 MAX inherently unsafe, because the stabilizer cannot be up-trimmed (nose-up) while up-elevator is applied ?

    • Rod says:

      If it suffers another rudder hardover, is the 737 inherently unsafe?

      Somehow I think that if enough bells and whistles are added, and the thing is tested to kingdom come as it ought to have been in the first place, the MAX will be a safe aircraft. (Whoa, do I like going out on a limb or what?)

      That said, Boeing — should it survive; should the worms stop spilling out of this-here can — won’t be fooling with no 737s no more.

      • Thomas says:

        The rudder-control hydraulic value had a design flaw, which allowed hydraulic fluid to push the rudder in the opposite direction to that which was commanded. The valve was re-engineered to correct the engineering defect. If it suffers another rudder hardover, the 737 is inherently unsafe, because another, DIFFERENT problem in the rudder power-control-unit will have surfaced, and Boeing Engineering practices will be suspect.

        But how is the engineering defect being addressed, which causes the aircraft to tend towards a stall, when it is overpowered rapidly ? MCAS is depended upon, to prevent the stall. And if MCAS is activated again erroneously, how will the aircraft stabilizer be re-trimmed, when the trim-wheel will not turn while up-elevator is applied ? Back-pressure on the control-column will have to be relieved, while the control-wheel is re-trimmed. I wouldn’t want to be on THAT flight !

        If another 190 people have to perish, because they designed a variant with an inherent stall tendency, there should be no mercy for those deemed culpable.

        • Rod says:

          “If MCAS is activated again erroneously (…)”

          But this is equivalent (to me) to the yaw-damper business. It was re-engineered, as you say. Well the MCAS is being “re-engineered” too — and all the redundancies that Boeing didn’t bother to incorporate originally (the penny-pinching boneheads) are now being added.

          “How will the aircraft stabilizer be re-trimmed, when the trim-wheel will not turn while up-elevator is applied ?”

          I’m no expert, but wasn’t this potential identical on all earlier versions of the 737 AND on the 707 as well, and wasn’t there a “roller-coaster” manoeuvre that used to be taught as a way of relieving pressure, in pauses, during which the trim could be hand-cranked back from disaster? I’ve HEARD that this actually had to be used on at least one occasion on the 707.

          I have Repeatedly Asked on this thread why “the trim-wheel will not turn”. Nobody answers. So I’m Guessing sheer force of passing air — at high airspeeds — against extreme pitch-angle of stabilizer overpowers feeble force of trim-wheel. Like trying to lift an elephant with one finger.

          • Thomas says:

            The trim wheel will not turn because the jack-screw for the stabilizer will not turn. The air pressure on the elevator is forcing the stabilizer in the direction opposite of that which the jack-screw is trying to move it.

            You’d better hope that the bottom of the roller-coaster is > 0′ AGL, or else you will have another 30 foot crater similar to Ethiopian 302. I would not want to be on that roller-coaster flight ! If the problems start at “low” altitude, the ground is going to be coming up at you pretty fast while the elevator pressure is relieved, and the stabilizer is in down-trim (nose-down), and you’d have to have nerves of steel to resist yanking back on the control-column to pull up the nose.

            I can’t tell you what things might cause the MCAS to trigger. Maybe a software bug — maybe a spurious electrical signal from a wiring short-circuit — maybe simultaneous bird strikes on both AOA sensors — or some other unplanned event.
            Since the MAX tends to approach a stall when overpowered rapidly, it is an unsafe airplane without MCAS. Does MCAS cause more safety issues than it solves?

            If another 190 souls are lost, because another MAX stalls, or another deadly, unrecoverable, runaway-trim occurs, there should be no mercy for those deemed culpable. Once the stall-proclivity of the MAX was observed, should the design of the variant model have been abandoned ?

  16. Rogier Wolff says:

    You compare the self-reporting of pilots to the self-certification by boeing.

    The thing is that strong “no punishment will occur if you report an incident” rule exists to help pilots from reporting incidents.

    On the other hand, Boeing saying: “Nope, you can’t sell that airplane you need to fix this and that before you can”, is very unlikely on economic grounds.

  17. Lee Taplinger says:

    What’s the reason Boeing didn’t stretch and repower the 757, a basically great aircraft, instead of the 737, a basically lousy aircraft?

  18. Chad H says:

    This shows the dangers of blindly trusting automated systems, or prefering their input in a conflict. Just because “human/operator error” accounts for a lot of problems doesn’t mean the computer (supposedly free of the human factor) is perfect.

    Automation is good, Automation is great, but in a human v computer battle, the human decision, not the computer decision, should take precedence.

    • Rod says:

      Yes and no. In Jakarta I think they simply couldn’t figure out what the problem was (i.e. it wasn’t a straightforward “Uh-oh, computer’s gone nuts.” They didn’t even know the thing was there. No MAX crew did at the time.)

      In Addis, the DID turn the thing off, but it still didn’t save them.

      And in Buffalo, the human overrode the computer (which was correct) and promptly got everyone killed.

      Probably computers have saved wayyyy far more lives than they have taken.
      There’s no way to know. We hear only about the crashes.

      It probably would be nice if there were a magic The-computer’s-going-bonkers-(yes-I-do-understand-what’s-going-on)-so-shut-it-off-and-let-me-handfly-this-thing-myself button. But that simply isn’t the way aircraft are designed.

  19. Rod says:

    Man, read this sobering piece and take in the implications. True, the 787 has been flying safely for — what? — eight years now, and there are by now nearly 600 of the things in the air.

    But the corporate culture that led to the MAX is the same one that built the 787. And maybe one fine day…

    Gotta love Negroni’s “South Carolina also offered Boeing a union-free environment as it is a right-to-work state. Not only would Boeing benefit from the lower wage expectations in the south, it wouldn’t have to deal with pesky union rules and grievance procedures at its new location.”
    Right, Boss Hogg always acts like Boss Hogg. And there are consequences, sooner or later.

  20. Dick Madding says:

    You’re not there, yet. The root cause is failure of one angle-of-attack sensor on each of the accident aircraft, and how damage occurred to that sensor. Reportedly American & Southwest have never had an AoA sensor failure in their Max 8 fleets. That would equate to something approaching 500,000 cycles. Sherlock would conclude that something damaged these sensors on the ground. I’m reminded of AeroPeru 602 and the taped-for-cleaning static sources. Here’s another Red Herring article that goes to prove my conclusion. Bloomberg found NO Max 8 AoA sensor failures in their research.

    Another 727 operational problem disclosed early in its life was revealed when 2 of them with passengers on board went into Lake Michigan descending into O’Hare. Unrecoverable high speed stall was the cause, but again it took two crashes to come to that conclusion.

    So the carriers’ contribution to the accidents was damaging the sensors on the ground, not detecting it, and crew not capable of handling the emergency situation (except for Lion Air’s jump seat pilot on the flight before the last one). You covered Boeing’s contribution. IMO Boeing exacerbated the issue by quickly agreeing that the aircraft should be grounded. They and the industry as a whole would have been better served by standing behind their aircraft, warts and all.

    • Carole says:

      So, the Bloomberg article claims about 140 incidents involving an AOA vane failure since the early 1990s. Given approx 36,000,000 departures worldwide since 1990*, wouldn’t that get you around the same % as 2 incidents in 500,000 cycles?

      Is the difference in most of the the outcomes in aircraft without MCAS because the planes didn’t fight their pilots to death in getting up in the air or back on the ground safely?


      • Rod says:

        I’m surprised in the Bloomberg piece to find no mention of the possibility that an AoA sensor provides accurate information but that every once in a while there’s something awry in the transmission arrangement, or MCAS itself, that misreads it. Less likely, no doubt, but why count it out? “(The) sensor(s) (…), located near the nose of the aircraft, would have to malfunction or be damaged to cause the scenario suspected in the crash.”

        “(…) whether Boeing was too reliant on a single device to trigger an important change in the jetliner’s trajectory. Normally, aircraft manufacturers use multiple data points to guide a plane’s automated systems. Regulators, lawmakers and federal investigators are reviewing whether Boeing cut corners as it raced to get the 737 Max to market to counter Airbus SE’s A320neo aircraft.”

        Right. I have a feeling this is what was Really going on, and why Boeing didn’t expend the time and billions it would have taken to develop an entirely new aircraft which would have required no freaking-tweaking MCAS.

        As for “standing behind their aircraft, warts and all”, 0.6% of the worldwide fleet gone in survivorless crashes five months apart is one mighty hideous wart. As Carole says, MCAS didn’t merely fail, it wrestled these airplanes out of the sky.
        It was politically and commercially impossible for Boeing to stand behind the MAX as it was. It took the company costly days to grasp this, but it finally did.

        • Carole says:

          “…that every once in a while there’s something awry in the transmission arrangement, or MCAS itself, that misreads it.”

          Indeed. Quantas flight 72, an A330, pitched nose down at FL370 injuring 119 people, 12 of them seriously in 2008. One of the ADIRUs started outputting invalid data to the other systems. In response to the AOA data, the flight control computers commanded the plane to pitch down. The pilot used the sidestick to bring the nose back to level flight.

          After the 2nd, less severe uncommanded pitchdown, the pilots declared an emergency, diverted and landed safely with AP and auto thrust off. Pilots can apparently handle a great deal of issues when the plane doesn’t fight their every response to the situation.

          • Rod says:

            Right. And having ample height, and thus distance from the ground to shield them from disaster while they work things out, helps too. The Qantas crew had that. Though probably in the Indonesian and Ethiopian cases, they would just have simply had that much further to plunge.

            That Qantas incident was a weird one. Weren’t there two such cases involving the A330, and weren’t they both into or out of Perth? I seem to remember a coinicidence-I-think-not reaction in connection with a US/Australian military very-low-frequency facility in the area. That’s the thing with fly-by-wire: so many imponderables. As they say, the more you rely on computers, the more you’re relying directly on electrons in a quantum universe where things behave strangely and can wink in or out of existence unpredictably.

            And now for something completely different. To counter the one outright racist intrusion we’ve had, I had a look around youtube and found this brief video (seven years old) on Ethiopian Airlines. Really, not too long. Some pretty footage. Deals mostly the the pre-MAX 737.

          • Carole says:

            Rod, thanks for linking that video. The landing in the opening is pure poetry. It’s bookmarked. Great find!

  21. Ken Swanson says:

    Hello again: This article describes how engineers had to rebuild the 737 in such a way as to make it unnecessary for pilots to have to take simulator and other advanced training to legally fly it, which was undesirable for airlines because they like their pilots to be in the air, making money, instead of on the ground. See it at:

    On a positive note, I have designed an AoA indicator that is meant to be installed inside the aircraft, where it cannot be tampered with, hit by birds, or damaged by weather. It needs some analyzing by an electrical engineer, to interface it with a cockpit gauge. I have sent a document/drawing to Chesley Sullenburger who has expressed interest. I am not near anywhere that would have the lab and testing materials, to build it, but would like to see it be built and used, in memory of the 346 souls that died as a result of the MCAS system, and possibly bad or damaged external AoA sensors. Let me know if you have any interest in it’s development, and any access to trained electrical/electronic engineers, please. Nice to find a website where one can communicate with a real person! Feel free to email me….

    • Arfa says:

      Ken, an interesting concept.

      AOA is the angle of the airplane relative to its flight path. That is not the same as pitch angle.
      A question: How do you propose to measure the flight path angle without something external – like a vane – in the airstream?
      Also, note that indication would not be a stand-alone instrument. It would be electronic, on the pilots’ flight displays.

      Good luck with your project

      • Rod says:

        Good questions from Ken.

        Also, something tucked into the corner of an already crammed flight display isn’t my idea of handy. I’d leave it a stand-alone “steam gauge”, at least in the freaking MAX.

        Also, why Sully-upon-Hudson, the guy who made such a big public deal out the ETH first officer having such low hours before it turned out that it was at His initiative that the pitch-trim disconnect switches were engaged?

        • Rod says:

          JAYsus — uneditable posts. I meant questions from Arfa.

        • John says:

          “Also, why Sully-upon-Hudson, the guy who made such a big public deal out the ETH first officer having such low hours before it turned out that it was at His initiative that the pitch-trim disconnect switches were engaged?”

          Because Sullenberger doesn’t care about facts or evidence. He just looks for any opportunity to bash non-US, non-military or low houred airline pilots to prop up the unnecessary American 1500hr rule. Every other country in the world flies safely with 200hr ab-initio pilots as First Officers. Their standards would make some American “CFI to E-Jet Captain at 2500hr heroes” pale in comparison. These programs high incredibly high selection and training standards, meaning 1-2% of applicants get in, unlike the American standard of “1500hrs and a heartbeat” for airline recruitment.

          From a guy who had a whole movie starring Tom Hanks made about him and how he felt so sad that crash investigators and the media speculated and unfairly blamed him for not gliding to La Guardia, he has now done the same speculating and unfairly blaming these Ethiopian pilots who struggled with an unflyable aircraft and aren’t here to defend themselves.

          Sullenberger needs to apologise and then keep quiet about things he has no knowledge about.

          • Rod says:

            I agree that he should apologize, and probably will do so — after the cows have come home and the pigs have flown.

            I don’t dislike the guy so much. After all, HE didn’t come up “the hard way”. He too survived cut-throat selection to fly F-4s. But he’s an old codger (as if I ain’t) and, well, as you say. So he’s a reactionary. But he should watch his mouth, because he enjoys Great Public Respect.

            With apologies to Patrick, who accumulated Many hours teaching people like me to fly, such hours are not worth a whole lot in preparation for an airline career (though they may make certain things second nature, certain complex aerodynamic realities muscle memory, that could one fine day save your life — see the Gimli Glider).

            Apparently there are today 200-hour pilots at the controls of nuclear-armed military aircraft. So I’ve heard. Remember, though, that simulator time doesn’t count as flying hours. The very realistic sims of today are a Far Cheaper way of giving novices practice.

  22. Ken Swanson says:

    You’ve said it all, esp. about the counter intuitive nature of releasing the control column when every instinct says to keep pulling it back. It reminds me of driving a vehicle on ice, and running into a situation where one must let off the brakes to steer, but must also slow down. That right leg does not want to ease off the brakes for any reason, and unless you have had that situation happen to you enough to learn to ease off and pump the brakes gently, while steering, you will more than likely run into something that you could have steered away from. According to several articles that I read, Boeing did issue a directive concerning turning off the MCAS after the Lion Air crash, but did not include the releasing of the control column as part of the routine. I do not know if this is true, but if so, it would represent a deadly oversight in what should have been a working, not incomplete directive. I agree with you that no one would have built a plane with these problems on purpose, but looking the other way when one knows that safety issues are being overlooked in building a plane is criminal. Corporations that ignore safety for bigger profits, and know they are doing this, are guilty of a crime, just as I would be, if I sold you a car with a dangerous problem, and did not tell you in advance that the problem existed. Here are two videos that point at a scenario similar to what I described: and “Broken Dreams: The Boeing 787”

  23. mitch says:

    Jean, you are absolutely correct. Boeing screwed up – big time. Somewhere inside the company there are the engineers and managers who designed and approved this system. We may never know who they are, but Boeing knows. Worst of all, the designers themselves know. They must live with the guilt that their mistakes killed 346 people. Whether or not they face any consequences, their careers are over. Although they go on living, their lives are over. The years ahead will be – nothing. Just the overwhelming unceasing guilt. They are sentenced to life without parole, solitary confinement in a prison they have made for themselves.

    • Rod says:

      You’re right, of course, if that’s really what happened. (Didn’t the guy in charge of the fatal engine change on the DC-10 that crashed in Chicago kill himself?)

      Nonetheless, many Boeing engineers are now being quoted in the press saying that — call this protective fakery, or at least hindsight hide’n’seek — their hearts fell when they were told to start working on yet aNother version of the 737, that they realized this was a step too far, that they knew something bad was going to happen sooner or later (though they couldn’t say what exactly) — it was just the principle of overbreeding: one fine day it would become glaringly obvious.

      If the top brass at such companies get the sickeningly high salaries and other benefits they do, then the buck has to stop with them. And that knowledge has to be ever-present in their minds. As Patrick says, clearly nobody reasoned “Oh, let’s build a quick but defective aircraft that will sell like hotcakes however crash regularly” — if only because such an aircraft would be Bad for Business. So the brass has to Ensure that slipshod design simply Does Not occur.
      THEY ultimately control the pressure on the people subordinate to them.

  24. Jean says:

    Whom ever came-up with this MCAS software system without being able to foresee it’s short comings should all be fired!

    One AOA goes out should not cause a A/C to go down…

    • Rogier Wolff says:

      In theory it is not “.. and then the aircraft goes down”. In theory it is “… and then the pilot disables MCAS and flies the plane”.

      In practice that theory is possible: It is reported “something” happened on the day before the accident (I don’t remember which one). They had trouble, managed it correctly and lived to tell the tale.

  25. mitch says:

    Mark: the Denver Post article is another example of scandal-mongering by an ignorant reporter with an agenda, using equally ignorant and biased “experts”.

    The article said “Larger 737 variants cannot be used at what are referred to as ‘high/hot’ airports, . . . Certain U.S. airports are unsuitable for the Max 8″. The implication being that Boeing sold ETH an airplane incapable of flying their routes. That is total nonsense. Airlines do not buy airplanes hoping they will be suitable. It just doesn’t work that way.

    Ethiopian would not have purchased any airplane that was incapable of economically-viable operations from their home base. The Purchase Agreement – a very closely-held document, proprietary to Boeing and its customer – would have included guaranteed performance out of Addis Ababa. A typical performance guarantee would specify takeoff field length plus payload and range under customer-defined ambient conditions. There could also have been a mission guarantee, defining field length, takeoff weight, fuel used, and payload from a specific runway to an important destination such as Nairobi.

    Similarly for American, Southwest and United at their critical airports, including Denver.

    [for 737-7, -8, and -9 MAX field lengths go to:
    Click on “737MAX”. Scroll to pages 3-35 thru 3-58 of Boeing document D6-38A004 “737 MAX Airplane Characteristics for Airport Planning REV D” March 2019.]

  26. Jean says:

    Come on…the pilots had over 6 mins. to save the A/C while at 94% the whole time, making it over 5k plus feet only to lose it because of over air speed. I am sure they did everything that came to mind to save it.

    Maybe less speed and more air an time, they would have save it.

    • Carole says:

      Can you point out the place in the Boeing/FAA Emergency Air Directive issued Nov. 7, 2018 (after Lion Air and before Ethiopian) that tells pilots to disable the auto-throttles?

      Also missing in the Emergency AD is the part about how to free the locked up stabilizers so that the manual trim wheel will actually turn enough to trim the aircraft.

      In the spirit of helpfulness, here is the AD under discussion:

  27. PD says:

    Those who are criticising FAA for outsourcing parts of safety certification to Boeing, I think that’s the way forward in complex industries. “… architects, engineers, and builders were forced long ago — going back to the early part of the last century — to confront the fact that the Master Builder model no longer worked. (The End Of The Master Builder, The Checklist Manifesto by Atul Gawande). A lot of American pilot-authors and others have enriched my knowledge and kept my interest in aviation alive over the years. I think American prestige and leadership in aviation will endure despite Max.

  28. mitch says:

    If not stopped in time, a runaway stabilizer can be a controllability nightmare. If the mistrim is nose down, the pilots must pull the control column to maintain level flight. One or both pilots would have to pull even harder to climb. As the nose down mistrim increases, so does column pull force. Conversely, level flight with nose up mistrim requires column push force and nose-down elevator.

    A controllable version of this mistrim condition is demonstrated during test flying by a stabilizer-elevator trade – measuring how much column force and elevator deflection are needed to counteract one degree of stabilizer mistrim. Every degree of stabilizer mistrim requires several degrees of opposite elevator and rapidly increasing column force.

    Extreme nose-down mistrim can exceed the available elevator deflection and pilots’ strength. One or both pilots would have to wrap both arms around the column, prop their feet on the lower instrument panel and pull with all their strength just to maintain altitude. The more the elevators move up to stay level, less and less nose-up elevator deflection is available to climb. If the nose-down mistrim exceeds nose-up pilots’ strength and available elevator deflection, the airplane would enter an unrecoverable dive.

    • Rod says:

      “The more the elevators move up to stay level, less and less nose-up elevator deflection is available to climb.”
      In other words, you have only so much up-elevator available, and only so much muscle strength and endurance to apply it against a mistrimmed stabilizer, so if you’re using all that just to stay level, you’ll have nothing left to make the aircraft’s nose rise. Correct?

      mitch, I wonder if you can answer the following question. I don’t quite understand Patrick’s statement: “When the plane’s stabilizers are acting to push the nose down, and the control column is simultaneously pulled aft, a sort of aerodynamic lockout forms: airflow forces on the stabilizers effectively paralyze them, making them impossible to move manually.”

      OK, am I correct in assuming that the stabilizer is hinged (or possibly the entire spar is somehow hinged) in a way that the entire thing moves as one piece (for both stabs) as the jackscrew turns? And that this hinge is precisely in the fore/aft Middle (which would make sense to me)? So you’re going the “speed of heat” (apparently the Jakarta MAX achieved 300 kt and the Addis one much higher).

      A stabilizer with full forward trim would be subject to massive airflow force — like a flap deployed. But with elevator at neutral position, that force is equal Fore and Aft of the ‘fulcrum’ around which the stabilizer moves as it’s trimmed this way and that.
      (done run outta room)

      • Rod says:

        So, there you are with over-high airspeed because MCAS keeps making you dive (and because maybe you’ve forgotten the freaking throttles in the totally confusing mayhem). You’ve cut the electricity and are now trying to hand-crank the trim back from full-down.

        IF the elevators were in a neutral position, the airflow force on the stabilizer would be equal both fore and aft of the fulcrum and therefore that force on the aft part would be helping you bring the leading edge of the stabilizer down while that same force on the forward part would pressure you’d have to work Against.

        Now, if the other pilot pulls back on the yoke in an attempt to raise the nose, the elevators move up. This has the effect of removing surface area from the aft section of the tilted stabilizer, Which Means that you’re now getting Less Help from the airflow force aft while still facing the same force forward.

        In this situation, you simply lack the resources to move the stabilizer.
        Is this what Patrick is trying to say?

  29. Lash Canino says:

    How to interpret “intentionally reckless”? MAX did not enter service by accident – under pressure from airlines, its production was rushed and very much apparently not all the bases were entirely covered. Not sharing all the relevant information with airlines has in fact a faint scent of criminal negligence. Ditto the business with Boeing self-certifying its product. As for Boeing´s position on the market, the MAX deal may already be blown, considering how many people will likely be scared off the type forever, no matter what is said or done. And the carriers are aware of that. And act accordingly.

  30. Jean says:

    Is it possible that some one could have hacked into the 737 A/C system
    for sinister motives?

    Most parts/systems give you a warning before becoming totally failed.

  31. Jean says:

    The crash site should have been secured. I would bet that one could buy back looted A/C pieces and loved ones personal property at the local market.

  32. jean says:

    The report stated that the pilot had about 103hrs. , and the co-pilot had about 53hrs. In the 737 max 8. This fact my have played a role in this crash.

    • Gimlet Winglet says:

      Ok, think about just how hard you’re trying to find a way to blame the pilots. IT’S A NEW TYPE OF PLANE IN ITS FIRST MONTHS OF SERVICE. EVERY PILOT IS GOING TO START AT ZERO HOURS ON THAT TYPE.

      Face it: Boeing put a new plane out there that frequently (at least three times in 5 months among some 300 planes) subjects the crew to a cascading failure of multiple systems worse than anything they train for in the simulator. They failed to inform the pilots of the existence of MCAS. They failed to inform the pilots of MCAS’ behavior of 15 seconds cycling that includes a 6 second window where the pilots if they knew of it could re-enable electric trim for a few seconds of control. They failed to inform the pilots that extending the flaps even one degree would disable MCAS. Boeing did not reinstate the training (discontinued in 1982) for reducing aerodynamic load on a jammed stabilizer under manual control.

      The ETH 302 pilots followed their training and within 30 seconds of noticing the unwanted nose-down trim had completed the runaway stabilizer memory list. Their only error through the whole flight was in not throttling down at some point, and I have not heard anyone indicate that a max-loaded stabilizer can be manually trimmed at 220 knots, which was the airspeed when MCAS first trimmed down. When this scenario was run in the simulator with pilot teams from various US airlines, who had to know in advance what they were in for, some still failed to save the plane.

      • Rod says:

        Also, in a quote I posted below, a US pilot with 12,000 hours on the 737 says he’s seen airspeed “drop off the scan” of crews in far less stressful circumstances than these guys were facing.

        And somehow ETH manages to fly the 787 and A350 and other types all over the place Safely — a long tradition at the airline.
        As the French say, that means what it means.

      • Jean says:

        You left out a big part “pilot turned the MCAS back on”.

        Over 43K take offs and landings by the 737 max Airlines around the world with no problems, maybe just luck.

        Could the plane have been sabotaged, after all it is Ethiopia?

        Airlines should post for the fling public the total HRS. in the air
        that the pilot has by type of A/C. before boarding.

        • Rod says:

          >>You left out a big part “pilot turned the MCAS back on”.<<

          Yeah, I left it out. Why? Because it was obvious to them that trying to hand-crank the trim was Not Working. And the terrain — which was rising — was getting nearer. So time was running out. Desperate times, desperate measures.

          As for your wild sabotage theory, you should immediately contact Boeing. They'll be Mighty Relieved. Might Grateful. Slap their foreheads and exclaim: "Of course! Ethiopia! It's Ethiopia after all. What's all the bother about?"

          Here's a question: How many hours on type did the crews of the early, say, American Airlines MAX revenue flights have? Hundreds? Thousands?

  33. Jean says:

    They don’t no how to maintain or repair it. When they kill the white farmers, they starve to death. A lot of them still live like they did 2k. years ago. Third world croup shitthole.

    • Rod says:

      Wayull, odd then that Ethiopian Airlines has a fleet of some 70 aircraft that it flies to four continents with a very good safety record … something it’s been doing for decades. Kinda mystifying an hairthang, eh Bubba-Jean?

  34. Mark says:

    Denver Post headline

    “Boeing has called 737 Max 8 “not suitable” for certain high-elevation airports like DIA”

    • mitch says:

      The Denver Post said that? Why?

      Any airplane can fly out of almost any airport provided that weight is low enough and thrust is high enough to accelerate to takeoff speed within the limitations of the existing runways.

      Concerning DIA, one would have took at the flight manual’s takeoff charts, correct them for altitude and ambient temperature, then determine takeoff field length, speeds, thrust setting and gross weight – TOGW – for the assigned runway.

      But if DIA’s longest runway (16,000 ft) is available, there shouldn’t be any problems.

      • Gimlet Winglet says:

        “Boeing has called 737 Max 8 “not suitable” for certain high-elevation airports like DIA”

        “The Denver Post said that? Why?”

        I saw the Boeing quote in multiple places. I take it to mean, not commercially viable. Sure the Max 8 could fly out of those places some or even most of the time, but too many weather/temperature cancellations and passenger bounces due to weight and you’re losing money.

  35. jean says:

    Did the ground crew accidentally hit the AOA wing before take-off? Was it cracked?

    There should be video cams covering all flight lines and a/c parking areas at every airport.

    How about the pre flight inspection?

    • rovingbroker says:

      Jean asked, “Did the ground crew accidentally hit the AOA wing before take-off? Was it cracked?”

      It is thought to be a bird strike after takeoff.

  36. rovingbroker says:

    Aviation Week …

    “Pilots Say MAX MCAS Software Updates Prove Effective In Simulator Demo”

    “Boeing has demonstrated the old and new versions of the MAX’s Maneuvering Characteristics Augmentation System (MCAS) to pilots and regulators in its 737 MAX engineering cab simulator in Seattle. The MCAS is a new flight-control-computer (FCC) function added to the MAX to enable it to meet longitudinal stability requirements for certification.”

    o MCAS has three new layers of protection
    o Compares inputs of both AOA sensors
    o Pilots always retain pitch control authority over MCAS input to stabilizer
    o MCAS no longer repeats after 5 sec. if electronic trim inputs are made

    It is a long, detailed and informative piece.

    • Rod says:


      And too bad Boeing ever ended up putting itself in a position where it had to install an MCAS in the first place.

  37. Jean says:

    How come no one is talking about the onboard computer system fault codes, which should be viewed by ground crews and pilot before every take off?

  38. yayoo says:

    Why the A/P can not engage and auto disengaged after engaged?

  39. adam says:

    Another aspect that I’ve heard is that the throttles remained at Takeoff power, and the aircraft continued accelerating.

    Thus increasing the aerodynamic load and likely making the trim wheel virtually impossible to move.

    Whether slowing would’ve helped, who knows.
    Although I’m sure some training departments will likely play with it in the simulator

    • Rod says:

      Everybody agrees slowing would have Helped. Whether — ultimately — it would have saved them is another question.

      This has been covered below. See (for example) my post five main posts down.

  40. DRLunsford says:

    I thought I would mention an important point IMO made by above-mentioned pilot – when you disable the auto-trim, the trim state does not return to neutral, but stays wherever it is when the motors are disabled. So you have to be able to manually trim, and if it’s way out of trim on this plane, you’d better know how to do it.


  41. DRLunsford says:

    I gathered the same information from one of those YouTube mavens with 40 years of experience, half of in the the USAF.

    He said it’s not so much aerodynamic weirdness as plain old mechanics. When there is a lot of down-force coming from the stabilizer, there is a huge force from the jackscrew on the actuator nut – so you let the nose-down win for a few seconds and unload the stress, do some trimming then, catch and correct the nose-down, then repeat until good trim is established. Not only does this *not* sound unintuitive, even I, with 0 hours in a commercial cockpit, can easily understand it.

    This pilot says that SIM instructors would distract the trainee and surreptitiously alter the trim then require the student to manually re-trim. When the difficulty appeared, he would take over and show the right procedure.


  42. Dean Cully says:

    If I had access to a pre-accident FCOM (Flight Crew Operations Manual) for the MAX series, I’d verify that indeed the stabilizer trim system brake incorporated in the flight control mechanism to stop pitch-trim actuation when the control column is moved by hand in the opposite direction, was deleted from the MAX design.

    if true, was this detail made clear to pilots new to the MAX, and especially to those transitioning from the earlier variants? I assume it was, as the brake is in the systems training materials for earlier variants. So, this begs the question in my mind, at least: was there a reason given in the systems description for this change to the flight control system? If not, it would make one wonder why, given that it is a proven and reliable feature, and most crucially, a change to the flight controls’ operation. My understanding for the deletion is that it is related to the MCAS’s functionality; MCAS can’t override a theoretically errant pilot’s manual control input if that brake system is in place.

    So, what was Boeing’s stated reasoning for the brake deletion, as explained in the Differences Training materials? Such an explanation, it seems to me, would lead to a description of MCAS. But we know from reporting that MCAS wasn’t revealed in pilot training materials, even though two other trim system features, “Mach Trim” and “Speed Trim” operate automatically in the background, too; but we know about these from the published systems description. WTF, BAC?

    • Rod says:

      Thanks, PD. In a way it’s hard not to sympathize with Boeing (a little anyway). It’s customers (the airlines) didn’t Want anything too new that you actually had to spend money training people on. Boeing lulled itself into complacency, telling itself everything would be alright (just don’t bother the crews’ heads with the MCAS, that’s all).

      This was possible because Boeing didn’t need to walk in fear of the FAA. That’s the modern-day US for you, I’m afraid. Same with the “opioid crisis” — if you’re in bed with the regulator, you don’t have to worry about actually getting regulated.

      • PD says:

        Hi Rod, found the article interesting because it quotes a lot of engineers and pilots. Being a non-pilot, would like to hear from people here about certain observations in the report. It seems to indicate that the Max is not fly-by-wire. Is it true? Trying to learn more about stabiliser trims, came across a phenomenon called “running out of elevator” (Understanding Air France 447, Bill Palmer). Elevator doesn’t have range anymore for pitch movement because of position of stabiliser.

        • Rod says:

          The A320 (late ’80s) was the world’s first fly-by-wire airliner. Reason? Computing power, previously inadequate. (Read William Langewiesche’s “Fly-by-wire”.) Since then we have the 777 and 787, for example, though they’re dressed up to have their flight decks look like traditional non-fly-by-wire aircraft (big yoke, whatever) but don’t let that fool you. [Sure, ALL 737s aren’t fly-by-wire — you’re NYT article shows very well what a hodge-opodge of old and new the ’37 is.]
          I do think Airbus (being French and therefore loving abstraction) have gone too far with the tiny sidesticks.
          As for running out elevator authority, perhaps somebody with more expertise could explain that. (I’m still still struggling with “the lockout effect”.)

          • PD says:

            What I have understood is, the stabiliser can reach its extreme position in any jet, even ones without MCAS. It’s a possibility, perhaps rare. If you have altitude, I guess you are lucky. More time to sort things out. If you are low, I guess it can complicate matters. And when a stabiliser reaches an extreme angle, elevators are no longer effective. Recovery technique is different. That’s my understanding.

  43. Rod says:

    To Jeff and Speed — no doubt you’re both right. Monday-morning quarterbacking comes up with some excellent solutions. But the heat of battle is something else. I’ll just place a brief paragraph from Christine Negroni (she’s quoting John Gadzinski, a 737 captain with 12,000 hours in the airplane flying for a US carrier):

    >>“There are things that are going on that are way beyond what you would ever expect to see in any normal emergency you would have. They are going the speed of heat,” Gadzinski said. “In 20/20 hindsight, they should have clicked off the autothrottles and that would have made some of the problems they were dealing with a lot easier to handle.” But Gadzinski added that during the crisis he can easily imagine airspeed falling off the scan of the overworked pilots. He has seen it happen in far less stressful circumstances.<<

    And all those Monday-morningers who say they would have disconnected the trim as soon as they got a stick-shaker after rotation because the flaps were correct and power was set and Bob's yer uncle … Great, fellas. But suppose that was a Real stall warning because they had put the wrong weights in the FMC, so they've rotated 20 kt early? (I bet these things happen.) Then: Not so great, fellas.

  44. Richard says:

    Why the heck isn’t the entire MCAS system disabled by the big “A/P Diseng” switch on the MCP? Isn’t that the switch the pilots flip to tell the computers to “go away”, and let me fly the plane myself?

    • Dean Cully says:

      Because the MCAS, as I am led to believe (having no access to the 737MAX systems description materials) only functions when the autopilot is off, i.e., when hand-flying (its ultimate purpose is to guard against pilot mis-handling in certain unusual situations), and with the flaps retracted. Depressing an autopilot disconnect switch on an already off-line autopilot only makes a clicking noise. I imagine the takeoff was normal until the takeoff flaps finished retracting, typically somewhere between 1500 and 2500 feet of climb and above 220 knots. Then the faulty MCAS kicked in.

      You may then ask, why not engage the autopilot, thus inhibiting MCAS and letting the AP fly; after all, it’s permissible above 1000 feet (above ground level; in the earlier “Classics,” at least). That’s a fair question, and quite possibly a solution, except for one thing: the AP won’t engage unless the pitch trim is essentially neutral, no forward or aft pressure being applied to the control column. And once MCAS has wrongly started pushing the nose over, the trim system is in motion, prompting manual counter-action on the control column, thereby keeping the AP from being engagable, IF the earlier 737s apply as a model in this regard.

      I’m extremely disappointed in Boeing for not thinking through the MCAS’s shortcomings as designed and programmed, to the point of suing the company for negligent homicide, particularly in light of the jackscrew lock-up revelation.

      • Lash Canino says:

        Dean Cully: “Because the MCAS, as I´m led to believe /-/ only functions when the autopilot is off, i.e. when hand-flying (its ultimate purpose is to guide against pilot mishandling in certain unusual situations)”.

        Wasn´t the reason for introducing MCAS though to counter the inherent imbalance of MAX that´s liable to produce an uncommanded nose-up movement? And if so… can this tendency to pitch up not occur when the autopilot is engaged then?

  45. Speed says:

    The Wall Street Journal reports …

    “Pilots who have read the report say that is unusual. A pilot would normally moderate speed if encountering problems like the ones faced during Ethiopian Airlines Flight 302, they said. The accident report said the crew didn’t change thrust settings once the plane had become airborne. The plane, within about three minutes, reached its design speed limit and continued to accelerate, according to the accident report.

    “The excessive speed is a huge issue” since it made it more difficult for manual commands to move flight-control surfaces on the tail, according to John Cox, a retired 737 pilot, ex-crash investigator and former senior union safety official in the U.S. “I don’t think I have ever seen a 737 that far over maximum speed” envisioned by the manufacturer, he said.”

  46. Michael says:

    I’ve read about “little Herbie” in the 707, it was supposed to correct the inherent instability in that plane. Is MCS similar in that it was supposed to be invisible to the pilots? Also, is the Max as primitive as the NYTs says it is. I know you dislike that plane.

  47. Thomas says:

    Is this, in essence, the same problem which plagued the P-38 in World War II — that the elevator airflow became ineffective (disrupted) as the airplane approached supersonic speeds in a dive ?

    Thank you.

    • Thomas says:

      Why wasn’t the elevator effective in raising the nose of the aircraft ?

      • Thomas says:

        Two and a half minutes into the flight, the overspeed warning turns on. The plane had accelerated to around 400 mph with the engines still on full blast at 94% thrust.

        This was after the MCAS cutout occurred, but before trying to manually trim the stabilizer.

        Obviously, pilot-overload occurred, and the overspeed-warning was missed. This was a vital cue to reduce engine power.

        It appears the pilots reactivated the system that would trigger MCAS.

        The plane’s nose points down. The pilots tried to pull back on the control yokes to raise the nose. It wasn’t enough. The plane dove at a 40-degree angle. The last indicated airspeed show the 737 Max reaching 575 mph.

        Perhaps, if engine power was reduced to 70% – 80% N1, and speed reduced, the elevator might have retained enough authority to pull out of the final dive — but the mis-trim of the stabilizer might have been hopeless at this point.

  48. Jeff says:

    Throttling back will also reduce the pressure on the stabilizers and slow things up. Based on the reports they were at/around 94% full throttle and descending. Throttle back to idle. Disconnect MCAS. Neutralize the yoke and I think they would have been able to manually trim the plane.

  49. Rod says:

    (after a 24-hour breather) Interesting quote and link from Carole. And it prompts me to ask again what I already asked below. In fact, I’d be grateful to anyone with advanced knowledge for answering two questions I’ve already posed here but which have gone unanswered.

    1) Patrick speaks of “a design quirk of the 737”. OK, I did my best to follow his description: “When the plane’s stabilizers are acting to push the nose down, and the control column is simultaneously pulled aft, a sort of aerodynamic lockout forms: airflow forces on the stabilizers effectively paralyze them, making them impossible to move manually.”

    What I understand here is that you have the horizontal stabilizer tilted full pitch-down (leading-edge up) whereas the elevators are deflected full upward. The stabilizer – held in place by the jackscrew – is ‘tilted up’ against the airflow. At very high airspeed, the airflow force (exacerbating the overall aerodynamic load) must be incredible, and the force required to Tilt the leading edge Back Against the airflow is more than the control-surface-movement resources available, and with every additional knot of airspeed, the impossibility increases.
    Is this it? Does this make sense? (outta space)

    • Rod says:

      But why would this be specific to the 737? The DC-9 series (to take but one example) also has a horizontal stabilizer that tilts for trim (perhaps they all do – I just don’t know). So isn’t there a potential hazard of a runaway trim + overspeed causing this same scenario? (Yes, it took the ‘MCAS Runaway Stabilizer’ to confuse the bejeezuz out of three crews, but is this Really confined to the 737?)

      If you look at Carole’s link, the participants are discussing the “roller coaster” (or “yo-yo”) technique and they say this manoeuvre was also prescribed for the 707, and even cite an example of it saving the day At Low Altitude over Toronto (yikes).
      Well, there ya go. Not just the 737.

      2) Why is MCAS NOT needed with flaps extended? Especially in a go-around — with massive thrust increase and significant pitch-up – I would have thought it would be Especially necessary.

      • Dean Cully says:

        Re: 2), I suspect that the with any amount of flaps deployed (the leading edge flaps and slats also begin extending automatically with the first increment of trailing edge flaps), the aerodynamic problem that the MCAS is designed to address, simply doesn’t exist due to the flaps’ favorable effect on low speed handling.

    • mitch says:

      Rod, just about every jet airliner uses a movable stabilizer to trim out pitch forces. That began with Boeing’s 1954 707 prototype, the “Dash-Eighty”.

      The most notable exception was Lockheed’s magnificent L-1011 Tristar. It reversed the design by using a “flying tail” – the entire stabilizer moved to control pitch; a full-span trailing edge tab was used for trim. I was once seated by the window in a Tristar’s last row – on approach, it was fascinating to watch the entire horizontal tail bounce up and down as the pilot applied pitch inputs.

      • Rod says:

        Thanks, mitch. I’m not surprised to hear that on most types the ‘slow-but-solid’ jackscrew should govern the position of the entire stabilizer and that it should be the elevator that does the frequent moving.

        So what do you think about this “aerodynamic lockout”? Couldn’t it happen on all sorts of types out there, albeit in extremely unlikely circs? Seems to me it took MCAS to bring it to the fore.

        I agree that the Tristar was magnificent. The light plane I learned to fly in had the same system: all-moving stabilizer for pitch, and a trailing edge trim-tab. It always impressed me that this little thing could make such a difference in stick forces.

  50. Carole says:

    From a pilot’s forum:

    Extract from the Boeing 737-200 Pilot Training Manual February 1982 page 04.80.31. Edited for brevity
    Runaway and Manual Stabiliser – Recovery from Severe Out-of-Trim

    “In an extreme nose-up out-of-trim condition, requiring almost full forward control column, decelerate, extend the flaps and/or reduce thrust to a minimum practical setting consistent with flight conditions until elevator control is established. Do not decrease airspeed below the minimum maneuvering speed for the flap configuration. A bank of 30 degrees or more will relieve some force on the control column. This, combined with flap extension and reduced speed should permit easier manual trimming.

    If other methods fail to relieve the elevator load and control column force, use the “roller coaster” technique. If nose-up trim is required, raise the nose well above the horizon with elevator control. Then slowly relax the control column pressure and manually trim nose-up. Allow the nose to drop below the horizon while trimming. Repeat this sequence until the airplane is trim.

    If nose-down trim is required, slowing down and extending the flaps will account for a large degree of nose-up pitch. If this does not allow manual trimming then the reverse “roller coaster” can be performed to permit manual trimming.”

  51. Alan Dahl says:

    They made one big mistake that made it even harder to turn the trim wheels, they keep the throttles set at climb power rather than slowing down. This made the force needed to turn the wheel even greater it’s hard to say if at half their speed they could have overcome the forces involved but it would certainly have been more likely.

    There was a sure way out of their predicament but I admiit it’s counter intuitive. After hitting the switches they would have need to reduce speed until a safe speed for flap deployal, deployed minimum flaps and then turned the switches back on. This would have rengaged the electric trim system but without turning MCAS back on. It’s unfortunate there isn’t an off switch for MCAS only but the flaps can effectively serve the same role if the speed is slow enough.

    I can’t blame them for not figuring this out in the heat of battle though, especially with the mountains getting closer and closer but it’s certainly something worth testing in the simulator.

  52. Craig Blome says:

    It certainly seems possible that the yoke has enough mechanical (or servo assisted) advantage over the trim wheels to make it impossible to budge. The jackscrews are similar but larger cousins of the spring compressors used to change MacPherson struts on a car. If you’ve ever used one of those, you know that it takes a MAJOR effort to cinch them towards the end of the compression, and that’s with a ratchet wrench that I’m guessing provides roughly twice the leverage of the trim wheel handles (if there is a reduction gear between there and the screw then of course I’m off by whatever its ratio is). A typical coil spring has about 150 lb/in of resistance, so a compressor with two screws moved four inches might be working against about 300 lbs on the thread of each screw. I use synthetic gear oil on the threads to protect them, and it’s still a workout. I assume that the aerodynamic force needed to rotate a 737 about its pitch axis probably loads the jackscrews to forget-it territory when the elevators are hard over.

    That got long and rambling, but suffice to say no one can be expected to work out from Physics 101 what’s happening as they are trying to keep a plane from crashing. If it isn’t mentioned in the manual, then a potentially deadly trap exists. My question is, if this corner of the flight envelope is so rare that the documentation writers didn’t think of it, did it occur to the MCAS development team that they might be treading in an old forgotten mine field?

    • Rod says:

      How did it get forgotten? Why haven’t those mines been exploding every once and a while for half a century?

      • Craig Blome says:

        I don’t know. How many runaway trim incidents have happened at >300kts? Is that scenario run regularly in the simulator?

        • Rod says:

          Patrick writes “It’s possible, or probable, that the pilots of Lion Air flight 610 faced exactly the same situation, with the same result.” Did the accident aircraft in Jakarta come anywhere near 300 kt — I mean before the dive had become unrecoverable?

          And when you consider all the kajillions of hours that the 737 has flown in 52 years (and all the runaway trim incidents that must have occurred with that number of planes flying around — incidents that were well or badly handled), you’d think things would have happened that would have raised eyebrows about the 737 (the way the yaw damper did).

          I have no idea how many passenger aircraft there are out there that require — or ever did — something akin to a “roller-coaster” technique to be taught to their pilots specifically for that type.

    • Gimlet Winglet says:

      “It certainly seems possible that the yoke has enough mechanical (or servo assisted) advantage over the trim wheels to make it impossible to budge.”

      I think the problem is that stabilizer in max down position with elevators in max up position exerts so much force on the jackscrew that a human can’t budge it. The force is coming from air pressure on the stabilizer and elevator surfaces. Nothing to do with who can pull harder on a yoke vs spinning a wheel.

      • Dean Cully says:

        Correct, just like a jackscrew device used for leveling a building; easy to turn by hand when not lifting anything, but requires a lever to turn when under load. The leverage afforded by the manual trim wheels (about 12″ in diameter with a fold-out cranking handle, normally plenty) simply wasn’t enough to work against the load exerted upon the jackscrew’s threads, no matter how well greased.

  53. Gimlet Winglet says:

    A few notes from the accident report:

    Immediately after takeoff left AOA sensor records an attitude of 74.5 degrees. Only some fighter jets can do this.

    2 seconds later First Officer activates deicing for AOA sensor.

    5 degrees of flaps used (not much, IMO consistent with a high elevation takeoff)

    2 minutes after takeoff flaps are retracted, MCAS immediately starts trimming nose down. Airspeed is about 260 kts.

    35 seconds later FO and Captain cut out electric stabilizer input.

    6 seconds later MCAS attempts to trim down, stabilizer does not move, indicating the cutout worked.

    1 minute 46 seconds after flaps-up FO tries to manually trim, reports manual trim not working. Airspeed is about 350 kts.

    1.5 minutes later they reengage electric stablizer input, lose the battle with MCAS and crash 32 seconds later. (remember they’ve been hauling back on the yokes with all their strength throughout)

    So, one stupid question: Is it possible to disable MCAS without losing electric stabilizer input by extending the flaps a small amount? Is that safe to do at 350 kts airspeed?

    (sorry for premature post below)

    • Dean Cully says:

      “So, one stupid question: Is it possible to disable MCAS without losing electric stabilizer input by extending the flaps a small amount? Is that safe to do at 350 kts airspeed?”

      I wouldn’t call that a stupid question. As an exercise in hindsight only, my answer would be “maybe.” I have no access to the the MAX systems description materials. So, going on what I’ve read in the press and what I know of the earlier 737s, if MCAS is only armed with flaps retracted, it seems that extending to at least position-1 would disarm MCAS, as I understand its purpose is to enhance control characteristics in the “clean” wing configuration, i.e., flaps fully retracted. If one were desperate for a solution and decided to try this, one would not worry about over-stressing and possibly damaging the flaps and their associated mechanisms.

      Flaps-5 is probably the most common takeoff flap setting for these airplanes, regardless of airport elevation. It certainly is in the older -300s and -400s I fly. Greater flap settings are available for takeoff, but single-engine climb gradient suffers greatly. Counterintuitively, Flaps-1 takeoffs are often used for increased SE climb gradient at heavier weights, the gist being that higher speed at liftoff (at decision speed/”V1,” actually) when an engine fails will net better climb performance during this most critical phase, rather than being slower and with more drag, even if perhaps higher at a given point just after liftoff.

  54. Gimlet Winglet says:

    A couple things I noted from the accident report:

    Left A0A sensor reported at attitude of 74.5 degrees (only rockets do this). 2 seconds later first officer activates the anti-ice heater for the AOA.

    5 degrees of flaps, retracted about 2 minutes into the flight. MCAS instantly started downtrimming the stabilizer when the flaps were retracted.

    35 seconds after flaps are retracted, FO and Captain cut out electric stabilizer trim.

    6 seconds later MCAS tries to trim nose down again, but stabilizer does not move (so the cutout seems to have worked).

    At 1 minute 46 seconds after flaps retracted, the attempt manual trim. At this point the airspeed is around 350 knots.

  55. Rod says:

    Patrick (re your latest update), Dean Cully — type-rated on earlier versions of the 737 — writes below: “According to what I’ve read in the referred-to April 3 Seattle Times story, up until 1982 Boeing included in its training manual an advanced ‘roller-coaster’ technique for loading, then unloading the control column and manually trimming until high resistance is felt, then repeating until a return to stasis., i.e., normal air load on the stabilizer and jackscrew mechanism.”

    This sounds like what you’re referring to. And raises a host of questions, to me at least. For example:

    — There must have been incidents — indeed crashes — that alerted Boeing to the need to develop a “roller coaster” manoeuvre, which sounds damned iffy and conditional to me anyway (e.g. make sure you don’t need to use it anywhere close to the ground, like the Ethiopian crew).
    Are we supposed to believe that some genius of a Boeing test pilot had this problem in the original version and saved himself by summoning this technique out of thin air, as it were? Sounds unlikely to me.
    Or were there crashes due to this to which other official explanations were assigned? (outta space)

    • Rod says:

      — If this was known about the 737, then it’s a Known Potentially Lethal Defect (like the yaw damper and MCAS would become), does it make more sense to [1] teach pilots a semi-aerobatic solution that — even if successful — would required every seat cushion in the cabin to be replaced and leave a planeful of passengers angrily telling anyone who will listen about it or [2] to fix it? Surely there must be an ascertainable aerodynamic reason for this (or one fully known to Boeing).
      Lockheed redesigned the Electra (where entire wings were coming off).
      Why — with So Many 737s flying all over the world for over half a century — has this not become the publicly known cause of major tragedies until now?

      — How was the deadheading pilot able to save the Lion Air plane on its penultimate flight? Or was there some significant difference between it and the ones that crashed?

    • not an anon says:

      The “roller-coaster” technique you describe was a test-pilot invention, but not by Boeing; I don’t have any inside knowledge to confirm it, but it seems to have its origins in what Bill Magruder and co. did to pull out of their supersonic test-dive in the DC-8, which apparently encountered a similar issue with being unable to move the stabilizer under airloads until they relaxed backpressure on the yoke. This was discussed, to the best of my recollection, in the Air&Space article “I Was There When the DC-8 Went Supersonic”, but I cannot find that article online any longer.

  56. Alan says:

    April 6 update:

    Egad what a nightmare situation. Although I can understand the lockout situation (would it be fair to say that the horizontal stabilizer is in a deep stall?) It is too easy to imagine that by the time a determination to push forward was made there would no longer be enough altitude left for recovery. Even knowing the correct control movements it would be really hard to do them.

    Another question is what were the pitch effects of the far-forward mounted engines? I thought that when they were at high-thrust they would tend to rotate upward. Which, intuitively is what you want but I suspect that a pitch oscillation would be a factor.

    The time of these incidents were in the post-takeoff climb. In these cases what was the thrust setting and could a recovery be made by changing it?

    • Gimlet Winglet says:

      The thrust setting was at 94% throughout the flight. More thrust won’t save you from a stabilizer trimming the nose down, and besides, they were already at 94%.

  57. Jonathan says:

    During the one and only dinner I ever ate in the company of General Chuck Yaeger (Joe Engle was also in the group), shortly after the Challenger space shuttle disaster, the great pilot ruminated on how this could have happened.

    General Yaeger recollected that when the X1 was developed, it was still possible for pilots and engineers to understand the functionality of the entire aircraft. Thus, to comprehend how changing A, could potentially affect B.

    As aircraft became more complicated, engineers became increasingly trapped in what are now called silos.

    They may well understand the functioning of the systems with which they were directly concerned. But it became increasingly difficult to grasp the big picture, because nobody could grasp the potential consequences of the various systems interacting with each other.

    This was a long time ago (1986) but I’ll never forget this analysis.

    In an engineering environment in which nobody can grasp the big picture, the only reasonable path is to test, test and test again.

    Boeing clearly failed. And the FAA likewise.

    It is tragic that the USA, for long the gold standard in aviation safety, has squandered this reputation.

    • PD says:

      One of the best analysis I’ve read. I wonder how the problems slipped through the test flights because I’ve heard the plane is taken through all possible flight envelopes during this phase.

  58. Dean Cully says:

    It seems now that the 737 Max crashes were the result, ultimately, of the stabilizer trim jackscrew being so heavily loaded by aerodynamic force due to high speed that the manual trim was either locked solid with friction or just too difficult to move fast enough by hand while close to the ground (departure climb phase).

    Finally, a plausible reason exists, other than the hard-to-believe or accept idea that the pilots were simply not competent enough to 100% hand-fly. According to what I’ve read in the referred-to April 3 Seattle Times story, up until 1982 Boeing included in its training manual an advanced “roller-coaster” technique for loading, then unloading the control column and manually trimming until high resistance is felt, then repeating until a return to stasis., i.e., normal air load on the stabilizer and jackscrew mechanism. Whereas before I felt that Boeing had an excuse of sorts, no longer.

    This new MCAS system should have been fully vetted by a larger brain trust that story-boarded out all conceivable failure scenarios while factoring the known-long-ago-(but-since-ignored/discounted) physical-mechanical limitations of the manual trim mechanism. I see no excuse for Boeing not accounting for the aero-mechanical limitations of its stabilizer jackscrew mechanism. Ralph Nader, whose humanitarian grand-neice was killed on the Ethiopian flight, is now fully justified in my eyes for directing his fury at BAC.

    • Dean Cully says:

      I say this as one who is type-rated in the 737 and currently employed with 1300 hours in type including the old -200s and -300 & -400 “Classics” in freighter configuration. Even though my initial training was in the -200ADV and with some 900 hours in airframes dating to 1982 or so, no mention of the pull-release technique was ever made or seen in print. However, the technique makes sense. I have to wonder if I would have had the instinctual wherewithal to try this–and with the surface just a few thousand feet below–even with 30 years of general aviation and commercial flying experience to my credit. I’m not sure. Sitting here in a café with the luxury of time and contemplation, it’s easy to visualize and seemingly obvious. If what I’ve read about a simulator experiment accurately demonstrating manual trim aerodynamic loading lock-up is true, that means it was a known factor because it was programmed in the sim as such. How could BAC ignore this, given the MCAS’s intended function?

      • Rod says:

        “The 737 Max crashes were the result, ultimately, of the stabilizer trim jackscrew being so heavily loaded by aerodynamic force due to high speed (… that is was) just too difficult to move fast enough by hand.”

        You mean the Addis crash. In Jakarta they were apparently too overwhelmed to realize that their core problem was mysterious electric trim inputs (from a system no-one had ever told them about…), and they never cut the power to begin with. As you imply, that’s no time or place to suddenly turn into Sherlock Holmes.

        “I have to wonder if I would have had the instinctual wherewithal to try this.”

        Right. Aircraft manufacturers have no business designing planes that can be safely flown only by ingenious and unflappable test pilots. Especially with rising terrain just out the window.

        If you’re type-rated on the 737, perhaps you can answer a question I have: Why, exactly, was it impossible to hand-crank the trim wheel fast enough to get the jackscrew back to acceptable? I mean, hand-trimming is hydraulic-assisted like other flight controls, Isn’t It? (Or not?) Was it that the building speed simply made All controls too stiff? Or that by this time, with the ground so close, it simply would have taken too many turns of the thing for it to be humanly possible? Both?

        It’s awful that they neglected the throttles. There but for the grace of God goes any and all of us.

        • Dean Cully says:

          The pitch/stabilizer trim jackscrew mechanism is actuated (rotated) entirely with cables (and probably sprocket chains), powered either by the hand-crank wheels or a pair of electric motors which operate singularly upon the cable-jackscrew system; the trim wheels (on a common axle at each pilot station) rotate when either motor activates. No hydraulics are involved. The primary flight controls are (redundantly) hydraulic-assisted (ailerons, elevators and rudder; the former two backed-up with cables and pulleys). Brakes, Landing Gear retraction, spoilers and nose wheel steering are also hydraulic (exclusively so); the flap system is electro-mechanically actuated. One trim motor is dedicated to the autopilot and the other to the yoke thumb-switch (L&R seats) for motorized hand-trimming (in the earlier variants), the usual technique/method when hand-flying. My guess is that the MCAS operates through the manual trim motor, as it reportedly isn’t armed when the autopilot is operating (however, I’d like to see proof of that). Each of these motors are powered through their respective cut-out switches just blow the flap handle, as explained by Patrick.

          Ironically, it seems to me, the whole purpose of MCAS and the entirety of the MAX’s advanced automation was to make the airplane as user-friendly and thereby safer to operate by the gamut of flight crews across the globe. I feel there was a profound shortfall in design and human factors analysis by BAC re MCAS.

          • Dean Cully says:

            AddenDUMB/correction: the flaps and leading edge devices are also hydraulically actuated, backed up by an electromechanical system for the trailing edge flaps only. I meant to double check that before clicking send. This is a good exercise in systems review, at least.

  59. Andrea G says:

    I’ve been really troubled by the media coverage and the comments I’ve read in aviation community forums and subreddits. There seems to be a very strong undercurrent of anti-Boeing, anti-FAA and weirdly, anti-American sentiment driving a lot of the discussion. There will be more than enough blame to go around, especially for Boeing and the FAA, but any discussion of the pilots’ actions and training & maintenance procedures of the airlines seems to be completely off limits. I hope these accidents are thoroughly investigating so that every contributing factor is identified and understood; that’s what has made aviation so safe. However I’m not very confident. (i.e. the ECAA gave the directive to French authorities to wipe the FDR/CVR data clean)

    • Rod says:

      Andrea G: “The ECAA gave the directive to French authorities to wipe the FDR/CVR data clean.”

      May we have a Source for this extraordinary statement?
      First, what is the ECAA? As far as I know, it’s a set of agreements. Since when does a Set of Agreements issue directives??
      I just googled “ECAA order erase cvr fdr addis” and got (drumroll) Nothing at all.

      Also, it’s hard to imagine the French authorities accepting such an extraterritorial “directive” (without laughing out loud, at least).

      It’s true that a lot of American pilots seem to hate the FAA. It’s their regulator. It’s like some drivers hate traffic cops and accuse then of all sorts of unhealthy attitudes and misdeeds.

      You’re probably right that there’s an element of anti-Americanism driving some of the discussion. (That would cover the anti-Boeingism as well.)
      There are practically always hidden agendas driving parts of almost any major discussion, a fact which makes me extremely curious about this ECAA business.

      • Andrea G says:

        I read 2 articles that stated the airline had requested the data be destroyed after the read outs/transcripts were provided. I’ll try to hunt them down. Until then I’ll put a slash through the parenthetical part of my previous comment.

  60. PD says:

    As the 1982 Boeing manual points out (The Seattle Times), the recovery procedure is more elaborate than simply hitting cutout switches and manually trimming the aircraft. Requires a thorough understanding of the aerodynamic forces acting on the stabiliser assembly, that one has to counterintuitively keep the nose down (despite MCAS) to unload the elevators to be able to trim manually. How high speed can complicate things. The recovery technique seems as demanding as recovering from a graveyard spiral. Without adequate training on simulators and with instructors, how is one to know the aerodynamic limitations of the recovery? The recovery technique offered by Boeing after the Lion Air crash is said to be inadequate. I wonder if airlines operating the Max tried it out on their simulators to find out the difficulty with manual trimming or anything else. As the Seattle Times report says, runaway stabiliser ceased to be a problem decades ago. So it may not have been a pressing training item for years till MCAS struck. As the 1982 manual points out, the aeronautical knowledge, so hard earned, is ythere, yet stowed away in an age of automated aircraft.

  61. Mark R. says:

    Ralph Nader lost his grandniece in the Ethiopian Airlines crash — now he’s taking on Boeing

    Social Sharing
    Family of Samya Stumo launch lawsuits against Boeing, Ethiopian Airlines, Rosemount Aerospace and the FAA

    CBC Radio · Posted: Apr 04, 2019 5:21 PM ET

  62. MW says:

    Here is a youtube commentary by a pilot on the report:

    So far, I’ve only read comments here on the Seattle Times report, but it looks like he has come to similar conclusions. This is my (non-pilot) summary of what he said:

    The pilots did not alter the thrust leavers, which were set appropriate for a climb, but with them barely keeping the plane level, it accelerated to overspeed. This made the difficulty of manually trimming even worse. Normal procedure is to let the nose drop to unload the jack screw to allow manual trimming – but they could not do this because they did not have the altitude to spare. It appears that, unable to manually trim, someone reengaged the electric trim system, which then let MCAS finish killing them.

    Reading between the lines, what the pilots needed to do was reduce thrust a whole lot, then crank really hard on the manual trim cranks. As I am not a pilot, I pass no judgement on their failure to find that course of action.

    • Rod says:

      Seems to me you’re quite right not to pass judgement. As so many people have noted, they were Overwhelmed. Here’s a quote (source: C. Negroni) from one John Gadzinski, a MAX captain with 12,000 hours in the various versions of the 737: “They are going the speed of heat. In 20/20 hindsight, they should have clicked off the autothrottles and that would have made some of the problems they were dealing with a lot easier to handle.” However, he points out, he can easily imagine he airspeed “falling off the scan” of the overworked pilots. He had seen exactly this happen in far less stressful circumstances.

      In addition to All the Other Things they had to deal with, according to the Ethiopian preliminary report, shortly after takeoff the stick-shaker “activated and remained active until near the end of the flight”. Of course the autopilot no doubt refused to accept any of the workload in those circs, so you’re handflying with a shaking stick. Great.

  63. MW says:

    Here is another pilot analysing the report:

  64. Hunter Handsfield says:

    Throughout aviation history, a central goal of airplane design has been aerodynamic stability: at a given power setting, attitude, speed, etc, stop control inputs (hands off, no autopilot) and nothing changes. Of course it does in real life, to a greater or lesser extent. But such stability almost always was the goal. It is said that some military aircraft don’t have this feature. Twenty years ago, when the stealth planes were new, they were described as inherently unstable, required by mission-driven design: without continuous compputerized trim input, they would be uncontrollable by human pilot inputs. I don’t know if this is also a characteristic of other military aircraft.

    Now it seems Boeing may have designed an inherently unstable airframe-engine combination in a commercial, passenger carrying aircraft — perhaps not to the extent as in stealth, but a design needing behind the scenes technology to provide artificial stability. If so, it is arguable lthat it should not have been certified: maybe Ralph Nader has a point ( At a minimum, the design should have embedded the multiple, redundant systems one expects in commerical aviation.

    Can the Max, or even Boeing as a commercial company, survive? It’s hard for me to imagine a technological fix combined with a marketing effort that can ever restore traveler acceptance.

    • David P. says:

      Thanks Hunter for bringing up the issue of aerodynamic stability.

      The issue of airframe stability seems to be an important concern regarding the 737 Max. The preliminary reports from Ethiopian 302 and Lion 610 indicate strong evidence for serious problems with the MCAS flight control system.
      However, why does the 737 Max have the MCAS in the first place? The 737 Next Gen was a reliable airframe without it. The underlying problem was that Boeing wanted to make the 737 Max as fuel efficient as possible – at all costs. The new winglets helped a little, a few minor changes also helped. However, the lion share of the improved fuel efficiency on the Max came from the improved jet engines. But, these had one big problem – the most fuel efficient engines had a significantly larger fan diameter than other versions. These new engines could not fit in the current position without coming too close to the ground. In other words, the new engines didn’t fit! So what did Boeing do?
      To solve this dilemma Boeing moved the jet engines farther forward and higher up. This allowed the required 17 inches of ground clearance, but introduced a major problem: The center of gravity was now moved forward. This engine placement gave the airframe an increased tendency to pitch upward under certain situations. This could pose a significant stall risk if left unchecked. In other words, Boeing choose to destabilize the 737 in order to maximize fuel efficiency!

      • David P. says:

        So, Boeing choose to destabilize the 737 in order to maximize fuel efficiency. Now what does Boeing propose? A software update, a few added warning lights, a little training. These could help – a little. But, will Boeing admit that they destabilized a reliable airframe?

        Also, imagine that you’re flying that updated Max – the angle of attack disagree light (that now comes standard) starts glowing. So, you turn off the MCAS. Now you’re flying a destabilized aircraft with a potential risk of stalling. Congratulations. If I’m on that Max I sure hope that we don’t have to do a go around on approach, make any sudden pitch changes or sharp turns, or any other quick adjustments. Any unforeseen events that would require an emergency landing or divert all of a sudden could become much more serious than they would have been in a 737 Next Gen.

        So, I am concerned about the underlying stability issue on the 737 Max airframe. This has truly been another tragic moment in the history of aviation. I can only imagine the grief that the friends and family of the 346 souls on board those two flights may be feeling.

        • Gimlet Winglet says:

          “So, you turn off the MCAS. Now you’re flying a destabilized aircraft with a potential risk of stalling. Congratulations. If I’m on that Max I sure hope that we don’t have to do a go around on approach, make any sudden pitch changes or sharp turns, or any other quick adjustments.”

          You are massively underestimating the basic flying competence of even the greenest FO. MCAS was added because FAA regs require stick resistance to increase proportionally to the amount of climb/dive the pilot is demanding. Instead tell the pilots the plane is sometimes prone to nosing up a little extra, they’ll recognize it and deal. By the time any pilot gets into the front of a civilian transport they’ve flown lots of planes with known quirks.

      • Hunter Handsfield says:

        Exactly my point. They made the airplane inherently unstable — i.e. the increaed upward moment due to the engines’ increased power plus forward placement — and decided to install an automated fix, rather than rethinking the basic decision. I have no idea whether there might have been a different solution to the design dilemmas they faced. But the bottom line seems to be that they chose to add a single-channel automated fix rather than either a) finding a different design that would maintain traditional stability or b) having a redundant fix not dependent on pilot training and skills.

        • Rod says:

          Hunterhandsfield: “Throughout aviation history, a central goal of airplane design has been aerodynamic stability: at a given power setting, attitude, speed, etc, stop control inputs (hands off, no autopilot) and nothing changes. Of course it does in real life, to a greater or lesser extent. But such stability almost always was the goal. It is said that some military aircraft don’t have this feature. Twenty years ago, when the stealth planes were new, they were described as inherently unstable, required by mission-driven design: without continuous compputerized trim input, they would be uncontrollable by human pilot inputs. I don’t know if this is also a characteristic of other military aircraft.”

          Appparently what made the Sopwith Camel such a fantastic fighter in WWI was its extreme instability (and thus the great difficulty of flying the thing). Because it was nearly impossible to successfully shoot at it, the Camel being able to flee in ways the pursuer simply couldn’t follow.
          So much for fighters, old and new (nothing to do with stealth, but rather manoeuverability).

          What you want in any other conceivable aircraft is inherent stability. The 737 Used to have this desirable characteristic.

  65. Rod says:

    Meanwhile, apparently the first civil lawsuit has been filed — against Boeing AND the FAA — in a US court on behalf of an American victim of the Addis crash. This is significant because:

    1) obviously, if you want to get at Boeing, best do it in a US court, and

    2) US courts, they say, have grown less willing over the years to hear cases involving events outside the country (such as an Ethiopian-registered aircraft crashing in Ethiopia).

    So maybe it’s a good thing that Americans were among the victims. Ironically, the victim concerned in the lawsuit was the niece of consumer advocate Ralph Nader.

    Meanwhile, to link two of Patrick’s stories, MAX-heavy airlines have big scheduling problems. Air Canada, with no less that 24 of the things (an eighth of its fleet, apparently), has had to cancel a number of services.
    So when WOW (yes, it’s difficult even to write such a silly name) went down the tubes last week, AC snapped up four A321s just like that. It has plenty of the A320 series, so numerous crew.

    • David P. says:

      The family of a 24-year-old American woman killed in the crash sued Boeing on Thursday. The complaint alleged negligence and civil conspiracy among other charges.

      “Blinded by its greed, Boeing haphazardly rushed the 737 MAX8 to market” and “actively concealed the nature of the automated system defects,” the lawsuit filed on behalf of the family of Samya Stumo alleged. Stumo is a great grand-niece of consumer advocate Ralph Nader.

  66. Alex says:

    And to think that if Boeing got its way, these models would still be flying. Kudos to President Trump for stepping in and taking action when the FAA was dragging its feet.

    • David P. says:

      A serious underlying problem with the FAA is the fact that it has a dual mission to both encourage and regulate aerospace travel. These dual roles can be contradictory. For example, to levy a heavy penalty upon an airline for violating an FAA regulation which would impact their ability to continue operating would not be considered encouraging aerospace travel.

      It is telling that the Canadian and European counterparts to the FAA have decided that they will conduct their own independent certifications to any forthcoming 737 Max update. Trust is clearly an issue at stake here.

    • Mark R. says:

      Kudos to the other countries that forced the Trump administration to follow suit. And best wishes to the lawsuits.

    • Gimlet Winglet says:

      Uh, it looked more like he upstaged the acting head of the FAA who was about to announce the grounding. And if you want to kudo, maybe you could criticize him for being in the 3rd year of his presidency without appointing a head of the FAA. Someone with more agency might have done something sooner.

  67. Carole says:

    From the Seattle Times today [4/4/19]:

    The stabilizer in the Ethiopian jet could have been in an extreme position with two separate forces acting on it:

    ∙MCAS Had swiveled the stabilizer upward by turning a large mechanical screw inside the tail called the jackscrew. This is pushing the jet’s nose down.
    ∙But the pilot had pulled his control column far back in an attempt to counter, which would flip up a separate movable surface called the elevator on the trailing edge of the tail.

    The elevator and stabilizer normally work together to minimize the loads on the jackscrew. But in certain conditions, the elevator and stabilizer loads combine to present high forces on the jackscrew and make it very difficult to turn manually.

  68. Carole says:

    From the Seattle Times today:
    The stabilizer in the Ethiopian jet could have been in an extreme position with two separate forces acting on it:

    ・MCAS had swiveled the stabilizer upward by turning a large mechanical screw inside the tail called the jackscrew. This is pushing the jet’s nose down.
    ・But the pilot had pulled his control column far back in an attempt to counter, which would flip up a separate movable surface called the elevator on the trailing edge of the tail.

    The elevator and stabilizer normally work together to minimize the loads on the jackscrew. But in certain conditions, the elevator and stabilizer loads combine to present high forces on the jackscrew and make it very difficult to turn manually.

  69. John says:

    With the revelation that the pilots DID follow the correct procedure, but even then were unable to manually recover from the situation that the MCAS had put them in, could we at least have an apology from those (starting from Sullenberger) who suggested that the pilots (and especially the First Officer’s) low flying hours were a big factor in the accident?

    When it was a discovered the FO had only 350hrs total time a lot of commentators mostly (but not all) American, readily threw him under the bus. Looks like the crew did their absolute best under difficult circumstances but were let down with a poorly designed product.

    That total amount of hours may look small to those in the USA but in most of the world it’s standard to have that amount of flying hours when being trained to fly an airliner like a 737 or A320. Ethiopian Airline’s training is considered one of the best on the continent.

    • BobsRight says:

      We still don’t know if the crew performed correctly or not. A big problem with both these crashes is that those country’s aviation authorities have been very slow in putting out the basic info, eg we still haven’t heard the CVR from either crash. But I agree, it now looks like the Ethiopian pilots correctly identified what was happening and at least started to follow the correct procedure. The big question is why they turned the electric trim back on. It could be they were confused and acted incorrectly. Or it could be that with full trim they realized that it would take too long to wind the trim by hand and wanted it back on to use electric to get it close to where it should be and they would then turn it off. Could be they ran out of time. Has anyone tried in a simulator to see how long it takes with a plane at that altitude, trimmed fully nose down,
      to wind it back by hand and how difficult it is? Is it possible that going fast enough and with full trim, it’s impossible to wind it by hand?

      • Gimlet Winglet says:

        “Has anyone tried in a simulator to see how long it takes with a plane at that altitude, trimmed fully nose down, to wind it back by hand and how difficult it is? Is it possible that going fast enough and with full trim, it’s impossible to wind it by hand?”

        Yes. There was a NY Times article about a week ago that described the results of 737 Max simulator tests conducted AFTER the crashes, using experienced pilot teams from multiple airlines, and testing the bad AOA sensor scenario. Basically, the pilots had 40 seconds to disable MCAS before the plane was trimmed into an unrecoverable dive. Remember that MCAS trims down for 10 seconds, then pauses for 5 seconds. 3 full 10-secnd trim-downs from MCAS and the plane could not be saved.

        The article did not describe the mechanics of why the (simulator) plane could not be saved. Perhaps because at large down-trim at high speeds (300+ kts) one simply cannot manually spin the trim wheels fast enough?

        • Rod says:

          There’s also this:

          The author’s fellow Swede, “MentourPilot”, is a 737-800 captain (probably for SAS) and apparently got his fingers slapped by his employer for putting up this video. They say it’s now been disabled on youtube.

          ANYway, I have a question: So you cut off the electricity supply, which means that you can’t use the stabilizer trim switch on the yoke and — far more important — MCAS can’t kill (they thought) you because it isn’t going to move the jackscrew if the trimwheels can’t move in time electrically on the flight-deck.

          However, doesn’t manual trim have a hydraulic assist like other control surfaces do when moved by a pilot handflying the aircraft?
          If not, why on earth not? Because if it did, I’m not understanding why vigorous aft trim by hand wouldn’t move that jack screw pretty quickly.
          Or is all this happening SO quickly that the human hand simply can’t spin it fast enough?

          • Gimlet Winglet says:

            “However, doesn’t manual trim have a hydraulic assist like other control surfaces do when moved by a pilot handflying the aircraft?
            If not, why on earth not? Because if it did, I’m not understanding why vigorous aft trim by hand wouldn’t move that jack screw pretty quickly.
            Or is all this happening SO quickly that the human hand simply can’t spin it fast enough?”

            I have essentially the same questions. The 737 was originally a fly by wire aircraft. You wouldn’t normally be manually dicking around with trim at near cruising speeds. I just don’t know, and I don’t think we’re going to get the answers anytime soon given the billions in exposure and the design errors in MCAS.

    • Seth says:

      I imagine in time we’ll have more information. The fact that the crew did disable the pitch trim system says they tried to do what everyone thought they didn’t do. There is a key question of timing. Did they do this immediately after the system engaged or did they do it after a series of dives and climbs, after which it may have been impossible to recover.

  70. Rod says:

    My apologies for posting so freaking often here. But this is the perfect story for such behaviour: long, drawn-out, high-stakes mystery. (I’m like Dr Strangelove — I keep trying to slap down my hand…)
    Anyone for a post-off? The winner will get a shipment of Patrick’s cheese-balls.

    Am piping up this time in response to JD’s post, since the system no longer offers a reply possibility (well yeah, it’s trying to shut us up).

    “My educated guess, which is probably wrong, is that Boeing didn’t want the MCAS activating too low. Pushing down to recover from a stall works great given enough altitude but not at very low altitudes.”

    Despite all talk of FARs and stick loads and whatnot, Ultimately MCAS is there to keep the MAX from stalling. Yes indeed, stall at low altitude and the ground shall rise up and smite thee.
    However, MCAS is about stall Prevention, not stall recovery.

    So I return to my question about why it’s inactive with flaps extended.

  71. Stephen Owades says:

    If the Ethiopian Airlines crew flipped the switches to disable electrical control of the jackscrew operating the rear stabilizer after MCAS had tilted that stabilizer by many degrees, they’d have had to crank the trim wheels quite a bit to return the stabilizer back to level. I wonder whether they realized just how many turns were required. Perhaps they gave up and restored electrical power to be able to use the thumbswitch controls when the plane didn’t respond right away to the hand-cranking.

    • Rod says:

      Why on earth would they fail to “realize” this? Wouldn’t hand-trimming pitch be part of their training? And, flying the MAX, hadn’t they pondered the Jakarta crash and its implications?

      Anyway, it’s said that investigators are having trouble interpreting just what the FDR/CVR are telling them. I find it hard to believe the crew would turn the power back on (knowing what they knew) but who knows what situation they were dealing with?

      AND people seem to be taking seriously the Possibility that there was another unknown/undocumented power mechanism in the MAX. That beggars belief, but it seems not to be ruled out (yet).

      HOWEVER, remember that the tower controller reported from the beginning that they were flying very fast (looked to him). I’m thinking of autothrottle complaints (apparently) about the MAX. Or what have you.
      At all events, the higher your airspeed, the higher the “airload” and the more effort it requires to move control surfaces. (This may be irrelevant here — I lack the expertise.) So maybe manual trim was simply out of the question.
      They were climbing toward rising terrain (not good). That means they were running out of Height to work with.

      It’s also said there will soon be an interim report (Addis). On the edge of yore seats everybody.

  72. Seth says:

    Just looking for some clarification about what’s involved in disabling MCAS. This article explains that there are switches. An earlier NY Times article described a procedure that was much more complicated. And if the system operates completely in the background, why would the crew start to disengage a system with no notification that it was engaged to begin with?

    Also, this article confirms what I’ve read elsewhere that part of Boeing’s fix is to have redundant sensors and to only trigger MCAS when both sensors agree that there is a concern with the angle of attack. How is this better? Let’s say that MCAS is necessary for this aircraft to maintain the proper flight feel. And let’s say that we suspect that these sensors can fail. Now, if a plane were to approach the dangerous angle of attack but one of the two sensors has failed, then MCAS may NOT engage when it needs to. Is this a solution?

    • Rod says:

      Ain’t no expert, but I notice that questions here often go unanswered. I’ll have a go. Maybe someone can offer a far better answer.

      1) If you think about the Lion Air flight that was saved the evening before the disaster by a deadheading third pilot in the jump seat, it drives home the point that – from the crew’s viewpoint — MCAS manifests itself in the pitch-trim system only. (At that point in the saga, pilots knew nothing of MCAS. Only after the Jakarta crash did they find out, and many were furious at being kept in the dark.) So, this guy had a view of the trim wheels in front of him, and it was probably clearer to Him than to the crew that (even with the mysterious five-second pauses) it was the trim system causing the nose to pitch down. And he said to himself “Man, that system has to be turned off before we crash.” He turned it off, the aircraft stopped behaving crazily, and all was well. The following morning, with no-one in the jumpseat, it went straight into the Java Sea. (done run outta space — rest below)

      • Rod says:

        2) “How is this better?” As I understand it, there always WAS at least one sensor (the aircraft was certified airworthy by the FAA with Only One…). Where else can MCAS get it’s angle info from?? I think it’s more the other way around: MCAS operates anyway, but if there’s disagreement between the sensors, the pilots are advised of this via a disagreement warning. So (and who knows what the Addis investigation will reveal?) presumably throwing those switches really does disable automatic trim. So now you have to hand-trim the aircraft (correct me if I’m wrong you pros). Big deal – that’s what those wheels are there for. Also, since MCAS can no longer manifest itself, you’re stuck flying an aircraft with a wrong feel to it as increased thrust pushes the nose up.
        Well, crews would need special training in safely flying without MCAS, something like Don’t forget a bit of forward pressure, then trim, when advancing the throttles.

        “Now, if a plane were to approach the dangerous angle of attack but one of the two sensors has failed, then MCAS may NOT engage when it needs to. Is this a solution?” Yes, but which one has failed? Nobody knows. All the system knows is that they Disagree. So it has no idea whether the plane’s approaching stall or not. That’s why the thing has to be turned off and the crew have to be Extra Careful flying it so as to keep it the hell away from stall territory.
        Great, eh?

        • PD says:

          That’s what a lot of reports say. Takeoff, I believe, is a task saturation phase. And now you have to stay prepared for a runaway MCAS. You have to first disable it and then apparently hand-trim the aircraft, all this during the busy takeoff phase.

          • Rod says:

            Except apparently MCAS doesn’t kick in until flaps are completely retracted, which doesn’t mean the business is totally over, but you’ve achieved some altitude wiggle-space.

            But this brings me back to MY question (which never received an answer). If MCAS stops working once you’ve extended flaps for landing (approach sometimes being high workload, especially if weather/traffic not good), and you have to go around, isn’t THAT a huge thrust input and a nose-up pitch change in any case? And no MCAS to compensate for stick-force weirdisms (which, to me, is just another way of saying to help prevent you from stalling)?
            This is something I really don’t undrestand — the flap business.

          • JD says:

            “If MCAS stops working once you’ve extended flaps for landing (approach sometimes being high workload, especially if weather/traffic not good), and you have to go around, isn’t THAT a huge thrust input and a nose-up pitch change in any case? And no MCAS to compensate for stick-force weirdisms (which, to me, is just another way of saying to help prevent you from stalling)?”

            My educated guess, which is probably wrong, is that Boeing didn’t want the MCAS activating too low. Pushing down to recover from a stall works great given enough altitude but not at very low altitudes. Without knowing the ground elev, the MCAS couldn’t rely on the altimeter alone. So as a fail-safe, it would only activate if flaps were retracted thus mostly guaranteeing the airplane was up to a certain altitude already. The other thought is that the increased lift/thrust feedback scenario only occurs with flaps at 0%, when the flaps are extended perhaps the lift characteristics don’t create the runway feedback due to the aerodynamics. Who knows the real answer (well someone from Boeing must), but these are the plausible guesses in my mind. But it still leaves the go-around risks that you mentioned. But…this is the crux of the matter…the aircraft is inherently unstable in certain thrust conditions.

            I also still wonder why AOS are failing? Yes ice, dust, debris, but shouldn’t they be more reliable? Hopefully a fix to improve the AOS reliability is in the works too but I am not hearing about that.

          • JD says:

            *AOA sensor, not *AOS. I never hear about improved reliability improvements for them after the incidents, just the MCAS software and training updates.

  73. Carole says:

    “…Boeing’s determination to keep the 737 line going, variant after variant, seemingly forever. Instead of starting from scratch with a new airframe…”

    The word I keep running into is ‘kludge’, defined as “an ill-assorted collection of poorly matching parts, forming a distressing whole.” The design of the 737 MAX was already a kludge and adding MCAS, for certification and airworthiness purposes, placed another kludge on top of the existing kludge.

    Apparently, all of this was Boeing’s response to the Airbus A320neo.

  74. mitch says:

    Several commenters have mentioned the sorely missed 757. Some have suggested it be brought back in a modernized version.

    Ain’t gonna happen. No way.

    The last 757 was made in 2004. The supply chain has long-since been dissolved. It’s Rolls-Royce RB2111-535 and P&WA 2037 and 2040 engines are no longer made. All the tooling was scrapped. The Renton engineering, production and assembly facilities were partly converted to 737 and P-8 use but were mostly torn down. The land was sold to commercial and residential developers.

    The fleet is aging and shrinking. Many airplanes have been stored. Many have been converted to freighters. Many others have been scrapped.

    The 757 is gone forever. Too bad. It’s a beautiful airplane.

    What really hurts is that its de facto replacement is the Airbus A321NEO – it’s about the same size with almost the same payload-range capability.

    • Rod says:

      “All the tooling was scrapped.” Ah jeez. Remember Rosemary Woods? You’d think it might be warehoused for a coupla decades as a precaution. What would that cost?

      Still, seems to me that Even Then, rather than further dig their graves with ever-further-tooled-up 737s (Peter Garrison nailed it), they should freaking well invest in new tools. Just the fuselage, tail and landing gear. They could use a new wing anyway, probably, and I’m sure there are attractive new engines out there.

      Or have they shredded the designs as well?

      • mitch says:

        Rod, as a Boeing retiree, I hate to write this, but yes the 737 airframe needs to be replaced. But how do you convince Boeing? They are a victim of their own success. There are (for now at least) more than 4,000 MAXs on order. If that backlog were to vanish due to massive cancellations – who knows what would happen?

        As for a 757 replacement, Airbus has that market segment locked up with the nearly-equivalent A321NEO. The 757 sold 1,004 airplanes over 22 years. Airbus has already sold more than twice as many A321NEOs.
        A slightly-stretched A322 with a larger higher-speed composite wing would be unbeatable.

        IMO Boeing’s medium size-and-range future lies in a “797” family. Probably a family of twin-aisle composite cousins of the 787, with sizes and payload-range capabilities that would replace the 737-8, -9 and -10 MAX, the 757, and early 767-200. But that’s for Boeing’s Board of Directors to decide, not us.

        • Rod says:

          I’m sure you’re right, Mitch. It’s just irrational 757-love speaking here.

          But Boeing had better Face Facts right quick if it wants any future at all. Of course, if the MAX business is an unfortunate episode, then it will pass and people will forget. But if it’s as worm-eaten as it looks from certain angles, Boeing might be in serious trouble. Some knowledgeable people think it is.

  75. JD says:

    We keep hearing about the MCAS. However, I also keep wondering one thing that nobody seems to be discussing:

    What is wrong with the angle of attack sensors that they keep reporting incorrect data?

    My understanding is that the vanes rotate to align itself with the airflow. Is it locking up somehow from dirt/debris? Or are they rotating correctly but it is being interpreted wrong by the computer system? Fixing faulty angle of attack sensors (or interpretation by the system computer) is also a critical fix that is needed by I don’t hear anybody discussing the cause and/or fix to the problem.

  76. Rod says:

    Is the Boeing 737 Max Worth Saving?

    Dunno about “the higher the nose gets, the higher it wants to go”, but otherwise this article seems to ask Patrick’s question. (And it quotes the peerless Peter Garrison…)

    Why don’t they just resurrect the 757 — new engines, new wing, glass cockpit, maybe do something to dampen the wingtip wortices — and let ‘er rip?

    • PD says:

      Very useful article. MCAS pushes nose down. Pilot tries to pull it up and soon the aircraft starts purpoising. After a few cycles, MCAS action and pilot response are out of phase and the situation worsens. The pilot falls behind the aircraft, much like a bad flare during landing when an aircraft bounces. Pilot action and aircraft response are soon out of phase and the situation worsens. The article also sounds a caution: that an MCAS that is not faulty may not be the solution.

  77. Eric O'Brien says:

    I have yet to hear an explaination of why Boeing decided to modify the FEEL of the 737 MAX (in certain flight situations) by altering the behavior of the ACTUAL FLIGHT CONTROL SURFACES, rather than modifying the code that drives the existing (!) Elevator Feel System. WHY?

    I also believe that the control column actuated stabilizer trim cutout switches are NOT OPERATIVE when MCAS is active. (I don’t refer to either the up/down stabilizer control thumb switches or the STAB TRIM switches on the middle console.) Absent any knowledge of the MCAS, pilots would expect that stick forces opposing trim would disable the trim motor, yes? They would be baffled that such opposite force did not disable the trim motor. That bafflement would just add to their confusion in a insanely stressful situation.

    Now if the existing Elevator Feel System had been modified instead, changes to feel would not rely on horizontal trim changes, which means the “yank stick to disable trim motor” gesture could still be function when the intervention was in play.

    • Ken says:

      I believe that the fundamental technical problem is that the new engines drastically changed the balance of forces at high AOA. I think someone noted below that close to a stall the 7373 NG would require significantly more control input to pitch up whereas the 737 MAX would require less (or not nearly as much more) control input.

      The business/ regulatory issue is, I believe, that in order for the MAX to not need a new type certification, the feel, particularly near stall, would need to be similar to the 7373 NG. I am inferring that changing the tail design to match the placement of the new engines might also trigger a new type certification.

      If Boeing could sell the 737 MAX without a new type certification, they could get to market faster and tell airlines that they don’t need more than an hour of new training for their pilots.

      It’s not hard to imagine the meeting where executives are told that they will need new type certification, and the executives say that they need to make sure it doesn’t as they have bet the farm and have orders pending based on the promise of not needing new type certification. They probably figured, “Let’s get it certified under the current type and then go back to the FAA with any updates.”

      That they didn’t tell pilots anything about MCAS and gave it more control than they told the FAA that it had is unforgivable. The fact that MCAS appears to be such a poorly thought out mess is just icing on the cake.

    • Eric O'Brien says:

      The article at that link continues to refer to MCAS as a stall prevention system, although it (briefly) alludes to feel. (“Designed to activate automatically only in the extreme flight situation of a high-speed stall, this extra kick downward of the nose would make the plane feel the same to a pilot as the older-model 737s.” Is that accurate??) I still have found no informaton about PRECISELY what “problem” MCAS was intended to address and how its behavior was intended to address that problem.

      Unfortunately, there is no analysis of why Boeing chose to alter feel by having software command movements of flight control surfaces. (Why not use the existing Elevator Feel System?)

      The article DID mention an important issue I have rarely seen in discussions: “In addition, the MCAS altered the control column response to the stabilizer movement. Pulling back on the column normally interrupts any stabilizer nose-down movement, but with MCAS operating that control column function was disabled.”

  78. Ken says:

    Sounds like Boeing is trying to keep the classification of an MCAS failure at the current level. If it gets raised, I think the system has to be triply redundant. That would require 3 AOA sensors, 2 wouldn’t cut it.

    Saw a story today where the pilots had 40s to deactivate the MCAS, or they wouldn’t be able to avoid a nose dive.

    Imagine that on a system that was not disclosed to US pilots. Boeing also didn’t disclose to the FAA that the amount of stabilizer deflection the MCAS could apply was increased by a factor of ~5.

    • Rod says:

      I was also thinking that “disagreement” merely tells you that you have to turn the thing off. But that leaves you flying an airplane that has the wrong “feel”, i.e. is ultimately stall-prone.

      Does “triply redundant” mean that the wayward sensor gets ‘outvoted’ by the two that agree? Didn’t something like that happen on AF447, and much good it did them?

      Anyway, seems to me that many mysteries will have to be unravelled before they can even start to solve this problem with any confidence.

      • Ken says:

        According to the FAA (AC 23.1309-1E) if the failure of the aviation control system (software and hardware) could lead to hull loss and multiple fatalities (catastrophic) , then the probability of failure would need to be < 1E-9 (less than 1 in a billion). A triple redundant system is one way to meet that requirement.

        It also specifically mentions that malfunction of autopilot is classified as catastrophic if it does not notify the pilot of error and it has unlimited control.

        Boeing apparently classified it as either "hazardous" or "major". The facts that AOA disagreement was an add-on that airlines had to pay extra for and that pilots weren't informed about EXISTENCE of MCAS unti after the Lion Air crash imply that it should have been classified as catastrophic and required 1 in a billion instead of 1 in 10 million (hazardous) or 1 in 100,000 (major).

        As far as 3 sensors voting, it's a pretty common method of protecting against a single-point failure. AF447 I believe responded as designed and went to alternate law after more than one pitot tube froze over. But I think that there have been some instances of the system selected the incorrect ADIRU when they disagreed. Though I'm sure it's much more complicated.

  79. Casey says:

    MCAS is not an anti-stall system, it was added to generate the correct elevator feel to meet FAR requirements. It is an addition to the Speed Trim System. It operates in a narrow range of the flight envelope because there are other stab trim systems that operate in the normal regime.

    The MAX is not unstable or prone to stall. The FAR for static longitudinal stability requires that the control column force needed to pitch up increases as the AOA increases. The engine placement on the MAX resulted in the elevator force decreasing as AOA increased when near stall, and that is not certifiable. So MCAS was implemented to meet the elevator feel requirement.

    All suto trim failures- STS, Mach Trim, autopilot trim, MCAS have the same remedy- stab trim cutout, revert to manual trim.

    All commercial pilots are expected to have memorized this procedure early in their training.

    • Rod says:


      Yet somehow there have been these two crashes, on the face of it quite similar. Something would seem to be happening that overwhelmed these crews.

      Note Patrick’s attached story about the last flight the previous day of the Jakarta accident airplane, on which a deadheading pilot was in the jumpseat and finally did hit the cut-out switches. Maybe the presence of that third pilot made it possible to see that the real problem was a haywire forward trim — something perhaps not obvious among the presumed cacophony of warnings and the struggle to control the aircraft and figure out why it was behaving so weirdly.

      An interim report or two wouldn’t go amiss.

  80. Rod says:

    I have a question that maybe Patrick or somebody else might answer: Why does MCAS become operational only when the flaps are retracted??

    If I understand correctly, the problem with the Max (and the reason a cyber-doodaw — MCAS — had to be grafted onto it) is that the engine position causes the nose to pitch up dangerously into stall territory when there is a major application of power.

    Well, if it’s needed with flaps retracted, why is it not needed with flaps extended. Yes, flaps put distance between you and the stall — but it’s perfectly possible to stall an airplane with flaps extended (as Colgan Air 3407 demonstrated).

    I’m thinking particularly of a go-around, where there’s a Major and sudden power application and the airplane’s trajectory changes swiftly from descent to climb. I realize that a 737 has a pitch attitude on final approach quite different from a business jet, let alone a light plane. But still, why were the designers so care-free about this nose-raising characteristic with flaps extended that they thought it was safe to leave MCAS switched off?

  81. Speed says:

    Aviation Week has a piece describing the changes coming up from Boeing.

    Boeing: MAX Changes Add Redundancy, Pilot Control

    SEATTLE—Key changes to the Boeing 737 MAX’s maneuvering characteristics augmentation system (MCAS) will incorporate more redundancy into the aircraft’s much-scrutinized flight-control law and give pilots ultimate elevator authority by limiting the degree of nose-down stabilizer command which the automated system can trigger, the company confirmed Mar. 27.

    • Rod says:

      To read the whole article you have to register (and presumably then sustain endless advertising harassment — which I ain’t doin’). Anyway, I’ve read about this elsewhere.

      I understood that MCAS was made necessary by the engine-placement’s tendency to cause the nose to pitch up into stall territory when power is applied. So if there’s disagreement between the sensors, the crews will now be explicitly warned that they are flying what amounts to an unstable airplane, liable to stall if they aren’t very careful? Sounds great.

      Obviously, hundreds of grounded airliners are costing companies Big Bucks, but I wonder whether this fix (why was the thing broke in the first place?) will reassure people. The dam has now burst about how the Max arose — it’s not sounding good. 0.6% of the existing fleet lies in little pieces.
      Seems to me that Boeing can implement all the fixes it wants, but a lot of uncomfortable questions are going to continue to be asked.

      Such as why the 737 was ever allowed to become and unstable airplane, why the second sensor was being hawked as an expensive accessory to an aircraft certified as airworthy without it by the FAA, and why crews weren’t even Notified of MCAS’s very Existence until a Max had slammed into the Java Sea.

  82. PD says:

    Just a layman’s wonder. When MCAS activates and pushes the nose down, should the pilot flying, against instincts, simply not pull back on the yoke? Some articles have said how counterintuitive it must have been for the Lion Air pilots. You pull the yoke but it produces the opposite reaction. The nose (as MCAS activates again) continues to drop. There is a line in Capt. Chesley “Sully” Sullenberger’s book Highest Duty. It’s towards the end of the chapter Managing the Situation, how a Captain has to “weigh everything he knows while accounting for what he cannot know”.

  83. Pat says:

    I have been a locomotive engineer for 30 years. Granted, the skill set and level of responsibility is substantially less than that of a passenger aircraft pilot. But over the years we have had computerized systems integrated into the locomotives. In every situation where a emergency action has been initiated by the system, my display screen will have a HUGE warning icon flash, along with the dreaded 6 beeps on the speaker. Drilled into our training is a reflexive action to take if this is not desirable. Along the lines of USAF BOLDFACE procedures. Just how many lines of code would it take for Boeing to show that the MCAS has been activated? The lack of this simple step in mind boggling. Add the single point failure design of the AOA inputs and the complete lack of mandatory training and to the mix and you have, in the mind of a lapsed Catholic, committed a Cardinal Sin.

    • Rod says:

      Since Patrick doesn’t seem to be saying much here, perhaps I can talk about light aircraft, which is my only direct experience. The trim lesson. The plane I learned to fly on had the pitch trim between the seats, which is convenient for stealthy manipulation. So we’re flying along and my instructor is hassling me about airspeed and continually warning me about outside scan — both designed to keep my attention well away from his left hand, which is busily trimming nose down.

      And I’m having more and MORE problem keeping airspeed down and altitude stable because the stick is getting so heavy and it’s becoming physically difficult to hold the nose up. And this is just a single-engine piston airplane. That shows you the power of a trim tab (or, in the case of the Max, the entire horizontal stabilizer) being set in an extreme position.

      Patrick would know, but I’ve heard that in the 737 simulator, with full forward runaway trim, it takes both “gorillas” up front hauling like Crazy on that yoke to counteract the trim. And that’s provided things haven’t gone too far speed-wise, as they eventually did over the Java Sea and, apparently, Ethiopia.

  84. Slarti says:

    I was wondering: When was the last time that a reasonably new plane had two or more fatal accidents within a short timespan (<1yr)?
    The DC-10 has been mentioned, but has it ever happened in "modern" plane times?
    I would agree that people have "accepted" that we can never avoid accidents completely and that every accident leads to a potential problem being fixed, making the plane even safer to fly afterwards. But I can also imagine that if it's proven that the (more or less) same problem led to two accidents, it will be hard to convince them the model is safe again.
    And, hypothetically, if Boeing would update the software and after some months another one crashed even remotely related to MCAS, the 737 would more or less have to be scrapped because passengers would refuse boarding one, don't you think?

    • Rod says:

      Maybe I’m losing my marbles (“Maybe”!?!) but I don’t recall DC-10s raining down from the heavens owing to an inherent fault. One, yes, in 1974 — and it was no joke. The Great DC-10 Scare’n’Grounding, however, didn’t occur until 1979, after the Chicago crash, which alarmed everyone but turned out to be a matter of bum maintenance. (Or do I have that wrong?) The DC-10 — once its cargo door (the cause of the 1974 crash) had been fixed — was a good airplane. (Didn’t ALL airliners have parallel hydraulic lines ….?)

      The most recent case of a serious design flaw that I can remember causing crashes was the (drumroll) 737, with a “yaw damper” inducing “uncommanded rudder movements”. At least this caused three crashes — two in the US and one in Indonesia (the latter is disputed, but as far as I know there is little sincere doubt) — over a six-year period.

      • Rod says:

        That said, the basic 737 design was already a quarter century old when these crashes occurred.

        Bum new designs? Can’t think of any. Thing is, so many (often painful) lessons have been learned in the 70 years of turbine-powered flight you almost have to go out of your way (like over-tweaking the 737) to make it happen.

        And natural capitalist concentration has squeezed it all down to a Boeing/Airbus duopoly. Not sure what effect that has on “new” designs. (The DC-10 and similar L-1011 were both sort of competitors with Boeing in the “jumbo” market. How times change.)

      • Slarti says:

        @Rod: Thanx for the clarification – I must have misread the reports about the DC10, thinking it happened in a short timespan. So if the two accidents turn out to be related or virtually the same type, that would be a first in modern times.

        • Rod says:

          I THINK so. But I’m no authority. As Patrick has pointed out, there have been potentially lethal teething problems (such as battery fires in the 787) but luckily the worst didn’t happen. Plane grounded, problem fixed, everything now OK (one trusts).

          But 50, 60, 70 years ago there were any number of engineering mysteries that simply had them beat, so you had the Electras and the Comets, and passengers saying “After you” — “No, after You” — No no, I insist, after You!”

  85. Siegfried says:

    Hi Patrick,

    As far as I understood, the MCAS system is only necessary on the 737 Max because of the larger engines. Is that true?

    Other than that, I agree with your analysis that this particular airframe was never meant to be used (or abused) as a large long haul carrier.

  86. Mark Oristano says:

    I’m just a passenger, not a pilot. But I wonder why the MCAS system wasn’t designed to work only at altitude. It seems to me that any stall counter-measure during takeoff or landing would be self-defeating.

  87. PD says:

    One of my favourite aviation books is Aloft by William Langewiesche (Patrick’s Cockpit Confidential is also a favourite). After the Max crash, read two of the chapters in Aloft once again, Valujet 592 and Columbia’s Last Flight once again. As people who care about flight safety grapple with the question: Was the Max crash avoidable, both the stories help explain why sometimes things go wrong. Valujet offers lots of insight on FAA, regulations, flight safety and why, according to Charles Perrow, Murphy’s Law is wrong.

    • Rod says:

      Hey PD, something we agree on: Langewiesche. All his books that I’ve read — including that one — are excellent.

      Yes, he puts his finger on a Culture of Negligence (or let’s say, at least, misplaced priorities) in both the Valujet and space-shuttle cases.

      And yes, were Murphy’s Law really true (in the cynic’s interpretation of it, anyway), the universe wouldn’t have made it past the first nanosecond.

      By the way, a highly reliable source tells me there was a coverup on the DC-10, so I withdraw that from my list of above-board human faiings.

      • PD says:

        Thanks Rod. I find your posts very informed. I guess large human enterprises have their own limits. The human factor, as they say. Still, aviation is way ahead when it comes to safe practices than many other human endeavours. Only Patrick can answer this. Why is they 737 tweaked forever? And not the 757?

        • Rod says:

          I was also wondering about the 757. The reason they had to shift weight so far forward on the MAX is that they couldn’t really raise the 737 very much (it’s a ’60s design, for a ’60s engine). But the 757 Stands Tall. So presumably you could put whatever you wanted underneath the wing, and come to think of it, give it a new, hyper-efficient wing. And a MAX-like glass cockpit.

          Yes, it would still have only one aisle, but where I live they happily board passengers front and back simultaneously, directing them according to their boarding cards. So it’s a rapid process.

          By the way, here’s an interesting video on the 737-200 and gravel runways, which predominate in the Arctic owing, I guess, to the havoc caused by the extremely low temperatures of winter (contraction) and the increasingly warm temperatures of summer (expansion). I’ve been to the grand metropolis of Tuktoyaktuk, which has a gravel runway. But 737s land there.

      • PD says:

        I believe all large organisations have thousands of workers who are conscientious, skilled and diligent, who raise these little red flags everyday. Why those are not heard or acted upon I guess can only be explained by human factor experts or experts on how large organisations function.

        • Rod says:

          I spent 30 years working in an organization to whose goals I’m firmly committed (pure luck that I ended up employed there) and which I greatly admire. When I started, there were about 250 people at headquarters, where I worked. When I retired, it was nearing 800. One reason was vast increase in sheer volume of work done by the organization. But there were lots of other unavoidable reasons (none of them was Bureacracy Run Amok).

          My conclusion after three decades of observing the place and its various units is that Any organization — private, public, whatever its purpose — numbering more than, say, 50 people is up against human nature. All sorts of inefficiencies caused by ego, careerism, bullying, empire-building, inability to see the Big Picture, whatever, will multiply as the thing gets bigger.

          In my late teens and early 20s I worked on assembly lines building railway cars and dishwashers (yep) in factories employing thousands of people. The stories I could tell about waste and inefficiency. But I think it’s inevitable when you get to that size.

  88. Ben says:

    What also concerns me about this 737 MAX fiasco is that Boeing is taking another giant safety gamble at this exact same time from folding wingtips on the 777X. I can just see those folding wingtips failing in flight and leading to a certain fatal crash early in the plane’s service life. If that happens, Boeing is going to be in even bigger trouble than it already is.

  89. PD says:

    FAA has attracted criticism for delegating parts of regulatory work to Boeing itself. The regulated is the regulator, some media reports have said. It’s a great newspaper story and assumes that it isn’t a safe way to certify a plane. There are stories that say Max 8 lacked safety add-ons. Well, even a basic plane can be safely flown. I believe their presence, or absence, doesn’t make a plane more or less safe to fly. What if all regulations were met and still things went wrong, something no one foresaw during design and testing. In the past also, aircraft have been certified fit to fly but design flaws were detected later. I don’t want to name any particular aircraft but there have been so many. It can happen to any regulator. You certify a plane fit to fly, then a flaw is detected later. I believe when inadequecies are found in regulations of the day, those are revised from time to time.

    • Rod says:

      I’ll name a few: the Comet, the Electra, the DC-10 and the 737 itself (yaw damper). Many lives were lost in each before the problem was solved. But they were the vagaries of technology that arose despite people’s best efforts, were honestly appraised, and dealt with promptly.


      (1) The problem in the above-mentioned cases was not due to over-teaking a fundamentally safe and proven design.

      (2)The faulty system was not still being designed even while the aircraft was already in production (because Boeing was racing with Airbus), an accusation levelled by People Who Ought to Know.

      3) The existence of the faulty system was not concealed from the crews operating the aircraft. (Yeah, the Comets eventually suffered metal fatigue, but everyone knew the windows were square and whatnot.)

      Yes, the FAA certified as safe a version of “the Max 8 (that) lacked safety add-ons”. Why would an airline pay good money for these add-ons if there was, according to the FAA, no problem without them?

      So you believe this is much ado about not a whole lot. Well, none of us knows for sure at the moment. It will eventually all be clear, however.

      Meanwhile, a pilot flying the MAX for a US carrier strongly disagrees with you and said so on the Aviation safety Reporting System well before the Addis crash and well before the recent non-stop revelations began to flow. This pilot was reacting to the Jakarta crash:

      (have run out of space – quotation follows)

      • Rod says:

        “I think it is unconscionable that a manufacturer, the FAA, and the airlines would have pilots flying an airplane without adequately training, or even providing available resources and sufficient documentation to understand the highly complex systems that differentiate this aircraft from prior models. The fact that this airplane requires such jury rigging to fly is a red flag. Now we know the systems employed are error prone–even if the pilots aren’t sure what those systems are, what redundancies are in place, and failure modes.

        I am left to wonder: what else don’t I know? The Flight Manual is inadequate and almost criminally insufficient. All airlines that operate the MAX must insist that Boeing incorporate ALL systems in their manuals.”

      • PD says:

        The views I have expressed are general in nature and not specific to the current incident. I’m not a pilot or an aviation expert, so don’t think I’m qualified to weigh in on the current crisis. Just being cautious without jumping to conclusions.

  90. Thomas says:

    Since pitch is probably the most critical axis of flight, I think I’d want the MCAS-switch FLASHING when activated, as a clue that it might need to be deactivated.

  91. Eric in NH says:

    Not so long ago, there were people who said, “If it’s not Boeing I’m not going.” There is a strong possibility that this could turn completely around to, “If it’s a Boeing I’m not going.” Garuda’s cancellation of their 737MAX order may be the start of this.

    That goes for the FAA as well. This is a textbook example of a phenomenon called regulatory capture. Instead of checking Boeing’s work as would have been normal in the past, the FAA allowed Boeing to self-certify the safety of the 737MAX. Among the potential consequences: I have heard talk of other countries’ aviation regulators no longer accepting FAA certifications. Which is a rational response if the FAA can no longer be trusted.

  92. PD says:

    When it comes to aviation, Americans have been the pioneers. But I guess even the best aviation system in the world cannot entirely prevent a Columbia disaster or a Max 8 crash. William Langewiesche discusses what he calls a ‘system accident’ in Valujet 592 (Aloft). Perhaps the Max crash is a ‘system’ accident. What is heartening, however, is the amount of debate and criticism of their own systems the incident has triggered in the US, within and outside FAA, within and outside Boeing, as well as across the country. Stakeholders have opened themselves up to scrutiny. There is so much information in public domain. Anyone who takes pride in the US aviation system is stepping in to fix the flaws. I doubt if that would have been the case if the plane was built in some other country. Goes to prove how close is aviation to Americans’ heart.

    • Rod says:

      I know I’ve posted a LOT here — maybe Too Much. But I can’t let this expression of American Exceptionalism (“the best aviation system in the world”) go uncommented upon. Don’t tell me that a similar case in another Western country wouldn’t get the same amount of critical attention, the same degree of open discussion, And Quite Possibly Far More Prompt Action. (Question: Which country was The Last to ground the MAX??) It’s pretty hard to imagine the degree of collusion between the the regulator and the regulatee in any other airliner-exporting Western country.

      And every day brings its load of new ugly revelations.

      As for Boeing, it’s public comment so far has largely consisted of a load of meaningless drivel, including the hilarious claim that its mission is to “protect freedom”. C’mon guys — that’s Grade-A Claptrap and we all know it.

      World public opinion will have the final say. Meantime, Garuda Indonesia has today cancelled its order for 49 MAXs on the grounds that people “have lost trust and no longer have confidence” in the aircraft. That’s the tip of the iceberg.

  93. Alison says:

    I am so disillusioned and disturbed by this current FAA that I don’t even know where to begin. And this was before the current situation with the 737 Max’s. I work with a local community group that has been trying to work with the FAA since 2015 to deal with the impacts of NextGen. (Noise pollution has exploded – several cities and states are currently suing the FAA over this issue). As part of changing the flight paths where I live, the FAA was required to do environmental impact studies, including showing new noise pollution patterns. The FAA said they did these studies. In over a year of asking, and making over a hundred FOIA requests to the FAA asking for proof of these studies, the FAA has not turned over a single document showing that they did the required studies. This leaves three possibilites: 1). The FAA simply never did any of the environmental studies they were legally required to do. 2). The FAA did them, but the results are so damaging, they won’t release them. or 3). The FAA is so incompetent they don’t even have anyone on staff to respond to FOIA requests. My money is on 1 or 2. Honestly, having now dealth with FAA “community relations” peope first-hand, and now hearing about how they’re so understaffed they let Boeing regulate themselves, and I’m honestly sad and incredibly angry that it has come to this.

    • Rod says:

      I think the FAA did do it — and acted on it — at Mar-a-Lago… 🙂

    • Dan says:

      Not a lot of sympathy here. The planes have to fly over someone’s house. NextGen allows more flexible routing, so they can spread out the traffic a little more. You don’t want them to spread it out over your house, you presumably want them to leave it where it was (over someone else’s house).

      Maybe, if they could spend less time on your noise issues, they could spend more time on safety of flight issues.

      • Alison says:

        That’s a pretty typical attitude of a lot of Americans these days isn’t it, Dan? As long as it doesn’t impact me or my well-being, I don’t care about anybody else. If you had done even five minutes of internet research on the issue, you’d see that the issue is far more complex and nuanced than your rather pithy remarks and understanding. But you couldn’t be bothered to do that, could you? It’s far easier to spout-off about something you know absolutely nothing about it, isn’t it?

        • Joe S. says:

          But it’s true. I don’t care about anyone else. I never volunteer or give money to charities. Humanity is unworthy.

  94. Dave says:

    So, on the day before the Lion Air crash, that very plane experienced an apparently serious “deviation” from normal flight. That article doesn’t provide too much detail and it raises many questions.

    Serious in-flight issues are required to be reported, are they not? Is it normal for an aircraft to fly so soon after such an event? Wouldn’t an aircraft of this sophistication be able to easily provide a computer “dump” of exactly what was going on during the flight on the day before the crash?

    • Rod says:

      Never been an airline pilot, but I think (Patrick will know) it goes like this:
      If anything serious happens, one pilot (probably the captain) takes control of the airplane and the other gets out a book containing the emergency checklists. (These days some may be electronic, which sounds like a very poor idea to me…) The second pilot looks up the problem encountered and reads out the steps recommended to correct it.

      Remember, we’re all human beings. Nothing recommends itself better than a checklist worked out in advance. If you’ve ever had to think through a complex system in an emergency, you’ll know why I say that.

      So, Freaking hell! They were looking at the freaking Handbook! probably means they were looking for the problem in the emergency checklist. I can think of no wiser course of action, though the poor guys had precious little time in which to do it.

      Lore: Enough airplanes had been crashed by crews so absorbed in solving relatively minor problems that they forgot about the job at hand that Northwest Airlines wrote in big bold letters on the cover of the binder containing the emergency checklists: FLY THE AIRPLANE!

      • Slarti says:

        Why “very poor idea”. Electronic in this context afaik means: On an iPad/Tablet. Sure, they have to make sure it’s charged all the time, but apart from that only advantages: No need for extra light, faster search than possible manually, always up-to-date, lightweight, etc.

        • Rod says:

          I say “poor idea” only because of my own experience with things electronic letting me down at the worst possible moment. I know I’m not alone. Whereas a wide, thin book in a slot Right Beside you that you can easily grasp, pull out and open on your lap sounds somehow more reliable. And there is absolutely No Reason why it wouldn’t be just as up-to-date as the electronic version (it’s a binder). Organized with easy navigabability and clarity in mind.

          As for lighting, there’s no reason why each book couldn’t be equipped with a forehead flashlight (that could, if necessary, be fit over an oxygen-mask-cum-smoke-guard).

          • Dan Ullman says:

            “Worst possible moment” is mostly a syllogism for not getting things after a deadline.

  95. Speed says:


    It is not a case of, “Oh look. It’s trimming nose down for no good reason. I’ll flip the trim off and re-trim by hand.”

  96. Speed says:

    “The AoA source

    “I had assumed that the AoA source for MCAS was always the Captains AoA probe but the following explanation from an engineer suggests that it alternates between AoA probes each flight:

    “MCAS is implemented within the two Flight Control Computers (FCCs). The Left FCC uses the Left AOA sensor for MCAS and the Right FCC uses the Right AOA sensor for MCAS. Only one FCC operates at a time to provide MCAS commands. With electrical power to the FCCs maintained, the unit that provides MCAS changes between flights. In this manner, the AOA sensor that is used for MCAS changes with each flight.

    “To summarise; MCAS will trim the Stabilizer down for 10 seconds (2.5 deg nose down) and pause for 5 seconds and repeat if the conditions (high angle of attack, flaps up and autopilot disengaged) continue to be met. Using electric pitch trim will only pause MCAS, to deactivate it you need to switch off the STAB TRIM SUTOUT switches.

    This makes sense. The failed AOA sensor causes the MCAS to drive nose-down trim. The autopilot is not involved.

    Go to the link to see what other instrument and control problems this presents to the crew. It is not a case of, “Oh look. It’s trimming nose down for no good reason. I’ll flip the

  97. Paul says:

    Just going by what I’ve read on all this, I’m struck by a remark I read once concerning how aviation accidents in general occur nowadays, perhaps Patrick himself mentioned this once. It’s the idea that due to the layers of training, checks, controls, fail-safes and so on that are now in place, it takes multiple things to go wrong for an accident to occur. Just one failure somewhere will not cause an accident, unless it’s accompanied by a failure somewhere else.

    With the MAX, an unfortunate combination of failures seems to have has occurred, at least with the Lion Air flight. You have faulty or malfunctioning sensors sending incorrect information to a new flight control system that has not been properly rolled out or introduced to pilots, who are thus unprepared and unable to react appropriately to an unexpected set of circumstances. Thus a hardware issue not properly dealt with has combined with a software issue not properly managed leading to human error.

    Maybe this indicates bigger systemic issues relating to pilot training in general, over-reliance on the technology and so on, I’m not qualified to judge that though. Certainly in the Lion Air instance, a question can be raised about the airline maintenance procedures and the sensor problem. And most certainly Boeing should rightly be scrutinised in how they rolled out the MAX. Without jumping to conclusions, they need to be asked the hard questions at least.

    • Speed says:

      Don’t forget that early in the chain of failures the AOA problem had been reported to maintenance at least once and not repaired.

  98. Dan says:

    “It’s becoming more and more clear that the same flight control problem that brought down Lion Air flight 610 last October was also behind the recent Ethiopian Airlines disaster.”

    Are you kidding me? Based on what?

    I see a plane taking off at 9600 ft. density altitude with a very shallow climb gradient. There were 157 souls on board. Assuming 30 lbs. carry on & checked baggage per person, 1,500 lbs. fuel for TO, 13,500 lbs. fuel for a 2 hour trip (includes 1 hr reserve), you are up to around 146,000 lbs. That’s without any cargo. At that weight, it would have taken around 8,000+ feet of runway to get off the ground. If they were ferrying fuel for the return trip, or carried any significant cargo, TO distance would have been closer to 9-10,000 feet. In any event, climb performance would have been poor, as shown in the altitude profile.

    At around 800 ft AGL, the plane started a rapid descent. That would be consistent with the pilot retracting flaps (required by the way to enable MCAS) at too low an airspeed, creating an incipient stall, followed by pitch forward (either by the pilot or MCAS) to recover. The altitude profile shows the plane recovering barely above the ground, saved either by MCAS or the pilot, or both.

    There is a steep climb after that and then an end of the radar data. So we have absolutely no idea what happened after the steep climb. Certainly, there is no data to indicate that MCAS triggered or operated improperly after the climb.

    • Rod says:

      Mind attributing your opening quote, Dan? (just a courtesy)

      At this point — 20 March — every last one of us is engaging in idle speculation. We Simply Don’t Know What Happened.

      That said and as Jeff BH has noted below, there’s a gripping article out from the Seattle Times, research for which began well before the Addis crash. It does Not cast a kindly light on either the FAA or Boeing.

      Also, Boeing has issued a perfectly laughable press release that says, among other things, (I’m not making this up) “Our mission is to … protect freedom …”. Sounds like Superman and a recent US president or two, eh?

      So let’s bear in mind that we don’t know anything about Addis for the moment (except that Something Very Bad Happened)and that Boeing and its “regulator” are in plenty of hot water.

      • Dan says:

        The quote was the second sentence in Patrick’s 3/20 update. I thought that was self evident, but I guess not.

        I agree that we’re all (including me) speculating at this point as to cause, but that was the point of my post. Patrick declared that it was “clear” that problems with MCAS brought down both flights. I offered an alternative explanation for what everyone else is saying looks like similar flight profiles. My purpose was to show that it was not “clear” that the same thing caused both crashes.

  99. James David Walley says:

    While everyone is jumping on the blame-the-MCAS bandwagon, there’s one detail that bothers me. Based on the VSpeed data, the Ethiopian flight was in trouble from the moment it left the runway…but the 737 does not allow for flaps-up takeoff (you get a very loud warning if you start a takeoff roll without extending flaps) and the MCAS system is disabled until flaps are fully retracted (which is why the problems with Lion Air didn’t manifest themselves until several minutes after takeoff). Is it possible the crew somehow managed to ignore the warning and improperly took off without flaps? Or was another bug found in the software that doesn’t disable MCAS when it should. I get the feeling we aren’t even close to having enough revealed to say why the second crash occurred, but those asserting it was “just like Lion Air” seem to be overlooking the one way in which the accidents were VERY different.

    • Rod says:

      I haven’t read anyone saying it was “just like Lion Air”. What I have read (including from the FAA and even Boeing) is that there are disturbing Similarities. Certainly for the second time in five months a MAX reported control difficulties, then went straight in, out of control. You can imagine both crews being barraged by all manner of warnings.

      Addis airport is at an elevation of over 7,600 ft (recall Patrick’s recent airspeed exercise) and was taking off toward rising terrain. Jakarta is practically at sea level and was headed out over the Java Sea.

      ANYthing is possible — open to idle speculation — as long as we have no authoritative published statement based on the analysis of both recorders and other relevant evidence.

    • Gimlet Winglet says:

      Thus my earlier question about what is normal flap usage for a takeoff at a 7600 ft elevation in fair weather conditions with a not fully loaded plane. Are the flaps retracted seconds after takeoff?

      • Rod says:

        If, as we’ve heard, they were headed for rising terrain, I think you’d want best angle of climb — whatever gives you that. Patrick — or someone directly familiar with the MAX — could tell us that, I suppose.

  100. Jeff BH says:

    The Seattle Times piece is devastating.

    Someone’s going to have to convince me that Boeing’s leadership shouldn’t be in prison and the company dissolved.

    (By “someone,” I mean Patrick, whose work I like and trust.)

    I know that sounds radical, but the cascading sequence of self-dealing, short-sightedness, indifference and greed that led to this, in both Boeing and the FAA (as described by the Times) breaks my heart. This is especially true as an American ex-pat in China who tells his classes over and over again that transparency and honest regulation are difference makers between the US and China.

  101. Tom Dietsche says:

    If this MCAS software depends on just one sensor to work properly (or not, as may be the case here), then that is a “single point of failure”. As good old Wikipedia says, “A single point of failure is a part of a system that, if it fails, will stop the entire system from working. SPOFs are undesirable in any system with a goal of high availability or reliability…”. No kidding!!
    So, assuming that is the case here (no secondary sensor data or other method of handling bad sensor data), why was this allowed? And, secondly, how many other SPOFs are there in these 737 Max planes, or other models?

    • Speed says:

      Tom Dietsche wrote, “As good” old Wikipedia says, “A single point of failure is a part of a system that, if it fails, will stop the entire system from working.”

      If failure of a single AOA sensor caused the airplane to crash while the autopilot was in control and neither pilot could disconnect the autopilot then it could classified as a single point of failure accident. However it appears (in at least one of the ASRS reports) that disconnecting the autopilot allowed the pilots to control the aircraft and fly safely.

      The pilots are part of the system.

      • Simon says:

        > The pilots are part of the system.

        I agree with all you said, but for these purposes, IMHO you can only consider the pilots part of the system if they are informed and trained properly about the automation (and changes to it). There appears to be considerable doubt as to Boeing and the FAA handling that part properly for the 737 MAX and MCAS.

        On an only partially related note, what’s the deal with the FAA apparently ‘outsourcing’ part of the review, validation, and testing to Boeing? How shall a regulator truly regulate, if they rely on the entity being regulated to do their testing for them?

        • Speed says:

          Simon wrote, ” … what’s the deal with the FAA apparently ‘outsourcing’ part of the review, validation, and testing to Boeing? How shall a regulator truly regulate, if they rely on the entity being regulated to do their testing for them?”

          I was concerned when I read that as well. I was more concerned about the FAA saying that it was underfunded for the job it was/is supposed to do. Many highly regulated industries (Food, Medicine/Drugs, Securities for example) rely on people within and paid by the industry for safety and regulatory compliance and this usually works well as long as the government agencies involved are diligent and competent at supervision, auditing and enforcement.

          It will be interesting to see how this shakes out. Aerospace is a huge industry with many interested parties including the taxpayers that expect safe, reliable and efficient airplanes.

        • M Schafer says:

          Simon suggests that the FAA should directly oversee all the Quality Assurance operations of Boeing. They are not ‘outsourcing’, instead they are partners with Boeing Q/A. FAA regulations require Boeing to document their processes and the execution of each and every step of design, manufacture, and certification.

          It’s much the same in the pharma industry where I worked. I never met an FDA regulator in my job, but I knew that every SOP document was kept for possible examination if a regulator requested it.

      • RobertT says:

        Unless a Wikipedia article has been locked, Wikipedia is not in itself a quotable source. The above “Wikipedia says,” should be the footnoted source cited in the article.
        The actual source: Designing Large-scale LANs – Page 31, K. Dooley, O’Reilly, 2002

  102. Tom in Vegas says:

    Outstanding article in the Seattle Times today about the development and FAA certification process for the 737 Max. Should, if accurate, address the issue. Outstanding. Would like Patrick to comment on it.

  103. Jim M says:

    I keeping hoping someone will publish a correction and amend the co-pilot’s 200 hours to “time in type” instead of total time. It’s hard to conceive of being qualified to fly a 737 in that amount of flight time even if it’s all instruction time. Hard enough to just get a commercial, multi-engine, instrument rating in 200 hours.

    An article on the subject of international copilot requirements would be interesting.

    • Rod says:

      Agreed that an article would be interesting, for light needs to be shed on this subject. I have twice the number of hours as the Addis FO, but all VFR single-engine hours accumulated as a weekend pilot: pretty useless on the MAX, eh?

      “Sully-upon-Hudson” (as Patrick calls him) made similar outraged remarks in an article I read about having a 200-hour FO. They were rebutted by two airline pilots as follows:

      “I’m sick of this tired old argument. You get your fATPL [Frozen Air Transport Pilot License] at 200-250 hours. In the States, you then muck around to get to 1500 before you can get an airline job. Lots of people instruct on a Cessna or Piper to build time. Hours on these aircraft contribute little to your ability to fly a complex jet in a commercial environment. In fact bad habits and attitudes acquired through years of general aviation flying may diminish professional capabilities of pilots. The fact remains that most parts of the world hire 200-hour cadets and have exceptional safety records because the quality of training is good and geared toward professional standards.”

      “There are people with barely more than 200 hours flying nuclear armed military aircraft over your country every single day. If the training is good then it’s a total non issue.”

    • Speed says:

      Jim M. wrote, “I keeping hoping someone will publish a correction and amend the co-pilot’s 200 hours to “time in type” instead of total time.”

      From the New York Times …

      “The chairman of Ethiopian Airlines said the co-pilot, Ahmed Nur Mohammod Nur, had 200 hours. Those hours were most likely in addition to the time he had spent learning to fly. According to Yeshiwas Zeggeye, a flight instructor with the airline, pilot cadets accrue 200 or more hours during their training.”

      Pretty weak. Imagine putting on your airline employment application, “I have 200 hours of experience in addition to the time I spent learning to fly.”

      • Rod says:

        Well, Speed, it’s pretty weak if you decide to interpret that it means he joined Ethiopian with a private licence plus 200 unproductive hours. And here he suddenly is.

        But we have no reason to interpret it this way, since the Ethiopian Airlines flying instructor talks about 200 Extra hours gained at the airline’s own academy (which it’s been running successfully for some decades).

        I dunno. Never been to an academy myself. But note the quoted remarks in the post directly above yours.

    • Speed says:

      Airbus launches ab initio Pilot Cadet Training Programme

      “The programme will be open to young people over 18 years old who have graduated from high school. Candidates will undergo screening tests online and on-site. The first batch of Airbus cadets is expected to start training in January 2019, graduating in July 2020. Similar partnerships are planned across the globe over the coming years.”

  104. I discovered AskThePilot through the Atlantic article on the Ethiopian 737 MAX 8 crash by James Fallows. I was a private pilot from 1976 to 1986 holding SE & ME Land, Instrument Airplane, and CFI certificates. I was gratified to see that James Fallows and you have brought fact-based, rational discussion of the 737 MAX 8 air crashes to the public media, which I hope will overcome the fear mongering media frenzy being spewed out by the “mainstream” media outlets to increase readership but leaving the non-aviation public feeling more distressed and fearful. Keep up the flow of “real” news.

  105. Michael Spencer says:


    The Ethiopians elected to send the two ‘black boxes’ to the Bureau d’Enquêtes & d’Analyses (France). They explained that the French agency might be a bit more neutral, as Boeing is in America; an opinion unfair to FAA, in my view, which could be blindly chauvinistic..

    Could you comment on the French as well as other agencies? How they compare to the FAA, in reputation as well as actual ability? Googling “reputation Bureau d’Enquêtes & d’Analyses” isn’t helpful.

    I’d expect the French agency to be world-class. Are they? What other agency in the world compares favorably to FAA? Am I correct that FAA is the ‘gold standard’? What of the Russians, or the Chinese, or the Brits, Canadians, Australians- that’s only the more developed countries. Are there labs in Africa, for instance, or non-Chinese Asia, that are capable? What of India?

    This entire episode is quite troubling, for sure. And thanks!

    • Rod says:

      Patrick is, as always, far more qualified than I to answer this. Just remember that the Ethiopians (as far as I know) haven’t handed over the Actual Investigation to the French. They’ve merely availed themselves of their technical equipment and expertise. I’m sure Boeing (as manufacturer) and the FAA (as certifier) will be looking over their shoulder.

      The FAA is a federal agency. Under the current administration, the websites of the Environmental Protection Agency, the Energy Department, the State Department, etc. were promptly scrubbed clean of references to climate change, greenhouse gases and clean energy.
      What does that tell you?

      So who trusts the US authorities to do this analysis with flawless professionalism? Clearly not the Ethiopians.

    • Simon says:

      I’d be wary of the FAA for the simple fact that they are both the ‘regulator’ and charged with promoting air travel and aviation. It’s an impossible situation to be in and I believe Our Favorite Pilot has also written about that issue.

      I don’t have any special distrust in the FAA, but as others have pointed out, government agencies have been politicized by the current administration and that does leave a bad aftertaste. In general I wonder if something like CDR/CVR analysis would be better handled by the NTSB with all their experience, plus them not also being mandated to promote aviation and airline manufacturers like Boeing at the same time as they’re investigating their products.

      I almost feel like it might be good practice in general to always go the investigators of a third country for technical analysis. Just like sending an Ethiopian MAX 8 recorded to France for example. Or in an Airbus crash in Japan sending the data recorders for analysis to the NTSB.

    • Speed says:

      Don’t confuse the FAA with the NTSB. Investigations are done by the NTSB.

      “In 1967, Congress consolidated all transportation agencies into a new U.S. Department of Transportation (DOT) and established the NTSB as an independent agency placed within the DOT for administrative purposes. In creating the NTSB, Congress envisioned that a single organization with a clearly defined mission could more effectively promote a higher level of safety in the transportation system than the individual modal agencies working separately. Since 1967, the NTSB has investigated accidents in the aviation, highway, marine, pipeline, and railroad modes, as well as accidents related to the transportation of hazardous materials.

      In 1974, Congress reestablished the NTSB as a completely separate entity, outside the DOT, reasoning that ” …No federal agency can properly perform such (investigatory) functions unless it is totally separate and independent from any other … agency of the United States. ” Because the DOT has broad operational and regulatory responsibilities that affect the safety, adequacy, and efficiency of the transportation system, and transportation accidents may suggest deficiencies in that system, the NTSB’s independence was deemed necessary for proper oversight. The NTSB, which has no authority to regulate, fund, or be directly involved in the operation of any mode of transportation, conducts investigations and makes recommendations from an objective viewpoint.”

      • Rod says:

        Speed, your link doesn’t work for me. I have every respect for the NTSB, which spoke the Truth to the FAA after the Valujet crash, for example. But these are strange times. Every entity dependent on federal government funds will somehow appear suspect in certain eyes.

        Anyway, the Bureau d’Enquêtes et d’Analyses (BEA)– some people following the AF447 investigation quipped that the A stood for Airbus — is no more in charge of the investigation than the NTSB would have been. I believe the Ethiopians are formally in charge (it being an Ethiopian-registered aircraft that crashed on Ethiopian soil). They just don’t have the highly specialized facilities to analyse the recorders.

        So let’s say that that the choice of France over the US is a symbolic protest at being sold a bill of goods: am airplane that supposedly required little extra training or experience to fly, relatively speaking.
        The Ethiopians don’t for the moment know any better than you or I what really happened, but they probably feel screwed by Boeing.

        • Speed says:

          Rod wrote, “Your link doesn’t work for me.”

          Try > About > History

          • Rod says:

            Thanks, Speed, got it. Again, the NTSB deserves our respect (and again, think Valujet). The passage in question, I’m guessing, is: >>In 1974, Congress reestablished the NTSB as a completely separate entity, outside the DOT, reasoning that ” …No federal agency can properly (do its job) unless it is totally separate and independent from any other …<<

            But I think that (1) no US federal agency is today immune, at least potentially, from missionary revisionism, and (2) the Ethiopians were sending a message (while probably saying "Hey, NTSB, Nothing personal.")

      • Eric O'Brien says:

        The URL needs some capitilization. (My suggestion would be to never use caps in a ULR path, but some sites do anyhow…)

  106. Ken says:

    I saw some flight tracking data that had the air speed at >300 kts! I thought it might have been a mistake, but now I just read elsewhere that the pilot reported higher than expected speed.

    Sounds like MCAS possibly kept throttle at TOGA while pushing the nose down. Would a pilot even be able to take time away from the yoke to shut off the MCAS. Would a very inexperienced 1st officer be able to turn it off in an emergency?

    • Speed says:

      From the Atlantic article linked below …

      “The Captain immediately disconnected the autopilot and pitched into a climb. The remainder of the flight was uneventful.”

      Autopilot disconnect is generally performed using a switch on the yoke. Disconnecting the autopilot also disables MCAS. To the best of my knowledge the MCAS does not control the throttles.

  107. Speed says:

    Gimlet Winglet wrote, ” … I’ve seen the first 3 minutes of the flight’s airspeed and altitude data as measured by ground radar … ”

    Ground radar can measure ground speed. If the wind speed and direction is known at the aircraft’s altitude, airspeed can be calculated.

    • Gimlet says:

      Your point is valid that ground radar sees groundspeed. The air temp at takeoff was 70 Fahrenheit and wind at 10 knots. The speed readings from ground radar do not show any sudden shifts in the first 3 minutes as if the plane got into some different wind at elevation, and indeed the plane never got higher than 1400 feet above runway elevation.

      So my questions remain, is 383 kts +/- 10 kts a normal speed for a 737 3 minutes after takeoff, and what would be considered normal flap settings and duration for a fair weather takeoff at 7625 feet elevation and a presumably loaded but not at the limits plane?

      • Speed says:

        Gimlet asked, ” … is 383 kts +/- 10 kts a normal speed for a 737 3 minutes after takeoff … ?”


        CFR says …
        “§91.117 Aircraft speed. (a) Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.). (b) Unless otherwise authorized or required by ATC, no person may operate an aircraft at or below 2,500 feet above the surface within 4 nautical miles of the primary airport of a Class C or Class D airspace area at an indicated airspeed of more than 200 knots (230 mph.).”

        • Gimlet Winglet says:

          Your reply is still non-responsive: The plane was more than 4 nm from the airport at the point where it reached 250 kts. The plane’s ground speed vs time tracks with other 737 max 8 flights departing from Addis Ababa. If the plane had followed a normal climb path it would have been both over 10,000 ft MSL and 2500 ft above the local terrain.

          So, unless I’m told otherwise, 383 kts is not an “abnormal speed” for 3:00 minutes into a flight, unless you have failed to climb. The plane did not have an “abnormal speed” problem, it had an abnormal altitude problem. Yes, if the pilots intended to fly at low altitude they should have throttled down. The had no such intention.

  108. Speed says:

    James Fallows has a piece in The Atlantic about ASRS reports from 737 MAX pilots.

    “Here’s What Was on the Record About Problems With the 737 Max”

    “While the fundamentals remain unknown, here are some relevant primary documents. They come from an underpublicized but extremely valuable part of the aviation-safety culture. This is a program called ASRS, or Aviation Safety Reporting System, which has been run by NASA since the 1970s. That it is run by NASA—and not the regulator-bosses at the FAA—is a fundamental virtue of this system. Its motto is “Confidential. Voluntary. Nonpunitive.””

    • Rod says:

      Thanks, Speed. I remember ASRS from pre-internet days — a blue paper you could get in the mail.

      Yes indeedy — “I am left to wonder: what else don’t I know?” Even if the Ethiopians were to emerge with little credit (we’ll see, we’ll see), the fact remains that, for commercial gain, Boeing was damn economical with the truth trying to sell airliners to customers by representing them as just (yet) another step in the endless 737 chain — another bit of cockpit familiarization. No expensive retraining on completely new systems.

      I knew I’d seen mention of autothrottles, and wonder if this could have a bearing on speed mysteries. (We don’t yet know what was going on up there. But suppose it was several things and the captain, with a 200-hour FO, was basically alone to face them all.)

      Finally, Fallows doesn’t wish to prejudge the FAA. I, however, will note that all federal agencies in the US these days seem to be undergoing a process of ‘ideological cleansing’. So why not protectionist cleansing too?
      The US basically waited until virtually the Whole Rest of the World had grounded the MAX before doing so itself. That does not inspire confidence. The Ethiopians strikingly did not bring the recorders to the US for analysis. I’d say loss of credibility has a lot to do with that.

  109. Gimlet Winglet says:

    There’s an NY Times report that claims “return after three minutes as the aircraft accelerated to abnormal speed”, without explaining what is meant by “abnormal speed”. Now, I’ve seen the first 3 minutes of the flight’s airspeed and altitude data as measured by ground radar, and the airspeed was NOT oscillating, but increasing at what appears to be a normal, constant rate. At 3 minutes into the flight the airspeed was 383 knots. Can anyone indicate if this is an unusual speed at that point?

    Also, a semi-related question: given that the runway elevation is 7625 feet, on takeoff would they be likely to deploy less flaps than usual and retract them sooner than at sea level? (Obviously we don’t know if the plane was “heavy”, though the passenger count indicates not a full flight.)

  110. Alan Dahl says:

    Let’s be a little careful of jumping into Boeing’s back until we know all of the facts. There are reports that the root cause could have been unreliable airspeed indications which combined with the mountainous terrain and a single pilot that was pretty much alone in the cockpit (because you or I would be as much use in an emergency situation) could have resulted in a loss of situational awareness and controlled flight into terrain. One of the reasons that flying is so much safer now is because of CRM, crew resource management, and that means pilots sharing the burden equally when an emergency occurs. I can’t see a rookie copilot with less time than a Cessna 150 pilot with a year under his belt being much help in this situation and perhaps could even have been a hinderance.

    • RobertT says:

      The Ethiopian first officer was not trained to fly a Cessna rather a jet airliner. 2,000 or 20,000 hours in a Cessna GA airplane would not qualify to fly a 737.

  111. One other thought/question. How come Boeing puts so much into all of the variations of the 737? They are trying to make various changes to that airframe be all of the planes they have ever made other than wide bodies….and even that – the larger variants compete with 757s and 767s nearly for quantity of seats. Why abandon the 757/767 programs? I suppose it is cheaper to make one model that suits all – and perhaps it is easier for airlines to train – but that being said – I cannot imagine there is much in common with earlier 737s and the newest MAX versions regarding pilot training. Your thoughts…?

  112. Captain Patrick – I knew you would pen a well-thought out and informative article about this situation. Yes – very sad and very tragic. But when you look at the overall picture the flight any of us take on any given day is probably safer than how we go to the airport or how we walk thru a city. I shared this on a number of social media pages. Nicely done. – Mike

  113. Ben says:

    There is a part of me with this still unfolding story that feels that Boeing has finally completely crossed the line with remaking and re-engineering the 737 to death with the MAX here. The 737 has been spliced into roles the were previously done by 3 other jets exclusively in the 707, 727, and 757. Boeing completely bit the low cost carrier bug here, and now it is finally coming back to haunt them with these two eerily similar crashes just 5 months apart. This could likely do catastrophic short, medium, and long term damage to Boeing if they are not careful, and it will get worse before it gets better.

    • Ababu says:

      Ditto Ben.

      Totally agree “Boeing has finally completely crossed the line with remaking and re-engineering the 737 to death with the MAX here. The 737 has been spliced into roles the were previously done by 3 other jets exclusively in the 707, 727, and 757. “

  114. Dick Waitt says:

    What we need here is a bit of Patrick’s common sense, especially as related to the chances of anything going wrong, even if it is eventually shown that this new system is somewhat at fault.

    What I’m saying is that, until this recent happening there have been probably thousands of totally safe flights of various versions of the 737MAX in its various versions. All were safely done (unless there have been other incidents of which we are unaware).

    Yes, it is a serious problem which needs to be addressed, but let’s not be expecting that the flight YOU are on will be the next failure.

  115. Lee says:

    First of all, any pilot flying a Max would know at this point how to disconnect the autopilot even if it’s a multi step process that wasn’t explained to begin with.
    Second, an Ethiopian farmer who witnessed the crash said there was fire and debris coming from the aircraft while still aloft. Which would have nothing to do with the autopilot.
    Based on that I could see why the FAA didn’t ground the planes.

  116. David says:

    Reminds of the saying never buy a car in its first year of production

  117. Richard Hartman says:

    I have seen one report that mentions smoke coming from the Ethiopian plan before the crash — this may indicate that something other than the MCAS was at fault this time.

  118. Michael Kennedy says:

    Not criticizing Ethiopia but one of the things we did in the sims at my last US airline before I retired was have the crews flew the plane with the trim completely AFU. (Some crews crashed but they got additional training) It’s a scary thing when the plane you thought you knew tries to kill you.

    Patrick, may remember the lovely SAS (stall avoidance system) in the Metroliner? Turning it off was the first thing you learned how to do.

    In my opinion Boeing screwed up by not telling the crews more about the MCAS and my guess is that the FAA is going to mandate lots of additional training. Which is how it should be.

    • Rod says:

      All bets payable only after fully functioning recorders are analysed and the investigation reaches some stage of certainty. Hey, maybe the Ethiopians did drop the ball — either in terms of faulty training or 200-hour FOs, or both. But that would hardly rehabilitate the MAX in the public mind.

      Or in the minds of some pilots, it seems. The complaints I’ve seen published from the FAA database, made by MAX pilots after Jakarta but before Addis, sound outraged and suspicious. Autothrottles too, I’ve read.

  119. Sharon Murphy says:

    I hate to fly, and the older I get, the more anxious I become when I have to fly again. These tragedies only make me feel worse. However, your articles always put things in perspective, and ease my fears about flying. Thanks for sharing your knowledge and insight.

  120. John Robertson says:

    Would Captain Sullenberger have been successful landing a 737 Max 8 on the Hudson?

  121. Alex Pun says:

    I feel like, for once, evidence and data (lack thereof) doesn’t matter this time(!). Now bear with me here… I know this site is, if anything, all about fact.
    By grounding the planes, Is the whole world jumping to conclusions? Yes. But somehow the way things evolved, this is no longer purely a question of 737Maxs’ airworthiness. Instead it seems to get more political or even GEOpolitical by the day. As in, FAA is now losing its public trust, and perhaps over the past four days it is deemed internationally irrelevant (even if just temporarily so). Had it been handled better perhaps we could have stick to pure facts (about the two crashes), but this is the Trump administration we are talking about. Not trying to be too political here: it is a bipartisan consensus that his tweeting often get himself and all of us into trouble. Boeing is certainly not helping by calling the president… Seriously, what good does that do?
    The fact that I am able to discuss FAA’s decision without mentioning a single technical data shows what kind of time we are in.

    • RobertT says:

      Boeing is a manufacturing company with a sales office. It cannot mandate its customers do anything. The US president can mandate, and enforce the mandate. It appears that Boeing’s management believed that its product should be grounded, so they went to the person who could do it.
      Other nations had already grounded the 737 MAX 8, some the 9 also. Others followed the lead of the other grounding nations, the USA or both.

  122. Simon says:

    Patrick, IIRC the AOA sensor was already a serious concern in AF447. Considering that this element is often described as a simple weather vane, yet this “simple” weather vane seems to also be prone to failure/error. Considering how important AOA signals are, is it possible these devices need to be throughly reengineered or otherwise, an alternative developed?

    • Matt Lyons says:

      Simon, the automation issue which led to the demise of AF447 was related to the failure of the pitot tubes (which use barometric pressure to determine the speed of the aircraft) not the angle of the attack sensor which measures the pitch of the aircraft. I’m surprised that Patrick did not mention the changes to the 737 8/9 MAX family of aircraft that necessitated the use of the MCAS software.

      Since the mid-2000s when oil prices became unstable, fuel efficiency has been the name of the game for commercial airlines, particularly in the U.S. Essentially, to make to the aircraft more fuel efficient than the previous generation, Boeing opted for a larger engine design, that while 14% more efficient, could only be accommodated by putting it further forward of the wing.

      This change was crucial since it altered the fundamental aerodynamic characteristics of the aircraft and the plane now had a tendency to pitch up during certain maneuvers. Enter MCAS as a software solution to address this design flaw which is unique to the 737 8/9 MAX series of aircraft. Boeing apparently did not think pilots needed to know about the software, which automatically adjusts the trim when it perceives the angle of attack to be too high, and did not issue an advisory bulletin as to how to disable it until *after* the Air Lion crash last October.

  123. Lyle says:

    The fact they had very experienced pilots flying manually or switching to autopilot when the antistall system kicked in suggests to me that due to poorer performance or undue restrictiveness of the automated flight parameters, (max vs ng) the pilots not being aware or trained climbed too rapidly for the Max.

  124. Mike says:

    Re: Ethiopian disaster

    You said in your Lion Air crash article: “The MCAS commands, faulty or not, can be overridden quickly through a pair of disconnect switches.”

    Surely (and if not, why not?) they can JUST SHUT THE DAMN THING OFF and fly the freakin’ plane until they figure this out! Not an Airbus so it is not totally fly by wire/software correct? Please err on the side of safety and sanity Boeing.

    Probably will when the next one happens. When, not if, unless they’re lucky.

    Millions of autonomous cars on the road soon? Yeah, right.

  125. Avery Greynold says:

    Was this a Boeing-engineered over-reaction to Air France Flight 447, where a couple confused pilots stalled a perfectly good A-330 into the Atlantic? Allowing an AOA system to overide them would have saved 228 lives that day. But putting all their eggs in one sensor’s basket may end up being even more costly.

    • Mark Maslowski says:

      I believe MCAS was installed because Boeing stretched the 737 for MAX, which changed the pitch characteristics, but they didn’t want to have to retrain those who were proficient on older models of the 737. Ironically, MCAS was supposed to be a safety net.

      • Rod says:

        Yes, pitch-up motivated MCAS, but not because of stretching the 737 (which Boeing has done endlessly) but the new, more powerful engines, which are set forward on the low-riding 737 and cause the nose to rise when power is applied.

        As for AF447, I’m sure this didn’t cross Boeing’s mind. The mystery there remains What caused the crew to be so confused (especially if the A330 was so perfectly good)?

  126. Tigersharktoo says:

    A couple of questions.

    Are modern jet aircraft really that close to the edge of stalling that they require automatic anti stall systems?

    Or is it just a 737 Max problem?

    Or is MCAS a solution in search of a problem?

    Why would not older stall warning systems work? What is wrong with the tried and true stick shaker?

    • RobertT says:

      In large aircraft the flight crew cannot rely on “seat of the pants” for impending stall. There are instances in which serious failures of the airplane to fly were not perceived by the pilots, inciting them to override the instruments and automatic safety devices.

  127. JD says:

    A few questions I’m waiting for from the investigators:

    Who was flying the plane? Was it the first officer with just 200 hours? If so did the captain take back over the control of the airplane? I just wonder how a pilot with 200 hours total is a first officer and if he received the proper training after the Lion Air crash or was he still just learning to fly period? Everyone commends the captain’s experience and training but nobody is saying the first officer was well-trained.

    Yes it was right after takeoff but how soon? More particular what was it’s altitude at the time of the issue? It could have been so low to the ground of course that even if the captain took control back (IF the first officer was flying) that there may not have been enough time to take the corrective actions to disengage the MCAS and regain control.

    Why are angle-of-attack sensors failing? Yes the MCAS is causing issues, but that software wouldn’t incorrectly override with nose-down actions if the sensors weren’t failing.

    Also I echo Ababu’s comment that Boeing has seemingly pushed the 737 too far. Maybe it’s just because I’m also a big fan of the 757, but I’d rather see Boeing improve that then try to make the 737 into a plane it’s not supposed to be.

  128. Ababu says:

    The 737 air frame is being asked to perform duties for which it is not designed. Boeing should have revived a variant of the 757, instead they cut corners and keep stretching the 737 beyond its air frame design limits with engineering gimmickry

    Reading from Wikipedia: “In November 2011, Boeing selected the larger fan diameter, necessitating a 6–8 in (150–200 mm) longer nose landing gear.[50][51] In May 2012, Boeing further enlarged the fan to 69.4 in (176 cm), paired with a smaller engine core within minor design changes before the mid-2013 final configuration.[52]

    The nacelle features chevrons for noise reduction like the 787.[53] A new bleed air digital regulator will improve its reliability.[54] The larger engine is cantilevered ahead of and slightly above the wing, and the laminar flow engine nacelle lipskin is a GKN Aerospace one-piece, spun-formed aluminum sheet inspired by the 787.[31]

    The new Maneuvering Characteristics Augmentation System accommodates the forward placement of the new engines while still retaining commonality (similar flying characteristics) with the Boeing 737NG family.”

    • Ben says:

      The point where Boeing stretched the 737 too far in length was with the 737-900 model in the late 1990s. They later came out with a mid life update to it in the 737-900ER. At the length of the 737-900/900ER along with the 737 MAX 9 and 10, it can be extremely tricky to land due to only having one bogie rear landing gear that takes the full brunt of landing forces. The similarly sized A321 and 757 have duel bogie rear landing gear that can hold more weight, and distributes landing forces over a wider area. This is where Boeing stretched the 737 too far. The 800/MAX 8 length is the longest length the 737 should have stopped at, and Boeing should have kept the 757 in production to cover that ultra stretched length.