Snow, Ice, and Airplanes. Everything You Need to Know About the Travails of Winter Flying.
IT’S THAT TIME OF YEAR AGAIN: storm warnings, preemptive cancellations, the mist and spray of that strange heated fluid splattering off the fuselage. Airplanes and winter don’t always mix well.
The flying part is easy. Sure, low visibilities, strong crosswinds, slick runways, potential icing — all of these things are challenges for pilots and cause air traffic backlogs, but as a rule they aren’t anything that airplanes or their crews can’t handle. It’s not the in-the-air aspects of a snowstorm that cause chaos, it’s the on-the-ground aspects: Runways and taxiways need to be plowed and treated, while tarmac logistics go to hell as snow and ice accumulate. Luggage and cargo handling, fueling — everything slows to a crawl as personnel and ground equipment become bogged in the slush.
Planes, meanwhile, cannot take off with ice or snow adhering to the wings. Parked at the terminal, an aircraft collects precipitation the way your car does — via snowfall, sleet, freezing rain or frost. (Thanks to supercooled fuel in the wings, frost can form insidiously even with temps above freezing.) The delicious-looking spray (apricot-strawberry) used to remove it is a heated combination of propylene glycol alcohol and water. It melts away existing snow or ice, and prevents the buildup of more. Different fluid mixtures, varying in temperature and viscosity, are applied for different conditions.
While it seems pretty casual to the passenger, the spraying procedure is actually a regimented, step-by-step process. Procedures vary depending on the type of fluid used, ambient temperature, plus the rate and type of precipitation. The airplane needs to be configured a certain way, and pilots stay in contact with the deicing coordinator throughout the process. The deicing guide in my manual is about 20 pages long, including several checklists, graphs and charts. We keep track of something called “holdover time” to help determine if and when a second round of deicing is necessary.
With fluid costing upwards of $5 per gallon, airlines loathe snowstorms almost as much as strikes, wars, and recessions. When handling and storage costs are considered, relieving a single jet of unwanted winter white can cost tens of thousands of dollars.
It’s money well spent, however, because ice on an airplane is potentially hazardous, especially when adhering to the wings. The monster isn’t the weight of the frozen material, but the way it disrupts airflow over and around a wing’s carefully sculpted contours, robbing a plane of lift.
Icing also can occur during flight. Under the right combination moisture and temperature, it can form along the leading edges of the wings and tail, along engine intakes and propeller blades, as well as on windscreens, probes, and various other surfaces. Left unchecked, heavy icing can damage engines, throw propeller assemblies off balance, and, just as it does on the ground, steal away precious lift. Planes are most susceptible during takeoff and landing, when speed is slowest and the lift margins already slim.
The good news is that most inflight ice encounters are brief and routine, posing little if any danger. Just in case, all modern commercial aircraft are equipped with deicing equipment. The various probes, sensors and windscreens are kept clear electrically. Engine intakes and wing leading edges are heated using air bled from the engines, or are deiced through a series of pneumatically inflated “boots” that break away accumulation. On propeller-driven planes, the prop blades are electrically heated. Whether pneumatically or and electrically-run, these systems use redundant sources and are separated into independently operating zones to keep any single failure from affecting the entire plane.
Planes also have sophisticated anti-skid systems to help deal with slick runways. Slippery runways and taxiways are in fact the single biggest threat during winter operations. If it’s icy or snowy, we get braking action reports, graded 1-5, or from “good” to “nil,” prior to taking off or landing. Anything below a 2, or if described as less than “poor,” and the runway essentially becomes unusable. Slipperiness can also reduce the amount of crosswind we’re allowed to take of or land with. A runway will further be off-limits if the depth of snow or slush exceeds a certain value, varying with aircraft type and carrier-specific rules.
There have been several ice-related accidents over the years. In 1992 a USAir jet crashed at La Guardia after attempting takeoff with inadequately deiced wings. There was also the infamous crash of Air Florida flight 90 in Washington, DC, in 1982, when in addition to buildup on the wings, frozen-over probes gave a faulty, less-than-actual thrust reading after the crew failed to run the engine anti-ice system. And in 1994 sixty-eight people died in what remains the deadliest-ever mishap involving a regional aircraft — the crash of American Eagle flight 4184 The plane, an ATR-72 turboprop, had made several circuits of a holding pattern in freezing rain, when suddenly it was thrown into an uncontrollable roll and plummeted from the sky, disintegrating in a soybean field near the town of Roselawn, Indiana. A design flaw in the ATR’s wing deicing system was later discovered, and corrected.
The most recent of those accidents was a fairly long time ago. Those were tough lessons to learn, but airliner crashes brought on by icing have become exceptionally rare.
Is it just me, though, or have winter storm delays become worse than they used to be? When I was a kid, a few inches of snow meant almost nothing. By comparison, nowadays, two inches of snow at Logan and the entire airport seems to go bonkers. What’s happened, maybe, is that our snow removal techniques haven’t kept up with the growth in air traffic. There are roughly twice as many planes flying as there were a quarter century ago, while our airport and air traffic control infrastructures have hardly changed. In the 1980s, closing a runway for 35 minutes so it could be cleared and treated had comparatively mild repercussions. Today literally hundreds of flights can be affected.
Meanwhile, airlines are becoming more and more conservative when bad weather looms, preemptively readjusting their schedules before the brunt of any storm actually move in. This is highly unfortunate if you’re one of the those whose flight is delayed or canceled, but things would likely be a lot worse for an even greater number of people had the airline attempted to push through. And remember that planes don’t simply fly back and forth between the same two cities; what happens in Boston or New York affects flights, and their passengers, further down the chain, in cities across the nation and the world. Drawing down the operation in one location helps protect passengers elsewhere.
Aside from the complications of ice and snow, airplanes perform better in colder weather. Some planes do have limits that prohibit operation when ground temperatures fall below a certain point (the complications here involve starting the engines, cold-soaked oil and such), but engines produce power more efficiently, and wings generate lift more efficiently, in colder, denser air. Very low temperatures occasionally result in delays and cancellations, but this more about the effects on support infrastructure: airport personnel and ground equipment — the various people, vehicles and machinery that go into supporting an airline’s operation. You can’t load and unload the luggage, fuel the tanks or cater the cabins if the baggage carts and belt-loaders aren’t working, the trucks aren’t starting, and employees are so cold they can hardly move.
Last winter was particularly nasty, with several big storms and thousands of cancellations. We’ve been lucky so far this season, but it’s only December.
For what it’s worth, crews don’t enjoy the chaos any more than passengers do. Airline crews often live in cities far from their crew bases, and must fly in to catch their assignments. With a storm looming, that means commuting in many hours early — sometimes a day or more ahead of schedule. Or, on the back end, we can find ourselves unable to get home again until things return to normal.
Once in a while, though, the timing works to our advantage. For example, how do you turn one pilot’s scheduled 24-hour layover in Brussels into a five-day European vacation? Easy, just send a snow hurricane roaring through the Northeast corridor, as happened a couple of winters ago. While the rest of you were stranded on tarmacs, sleeping under benches and sucking on discarded Chick-fil-A wrappers, I was sipping on hot chocolate and hopping on the train up to Ghent for a view of the newly restored Van Eyck altarpiece at St. Bavo’s Cathedral.
Not to rub it in or anything.
Photo by Patrick Smith.
“When you’re sitting on the tarmac while a guy in a hovering pod floats over you, twin beams of light piercing the murk of de-icing fluid. That’s my airplane fantasy. I want to be that guy!”
— Peter Hughes, Ask the Pilot fan and bassist for the Mountain Goats.