Everything You Need to Know About Icing, Deicing, and the Travails of Winter Flying.
Photo by the author: a deicing cab looms out of the mist at Logan Airport.
AS ANOTHER WINTER STORM bears down, about the last place you'd want to be is headed out to the airport. Delays and cancellations pile up, causing a ripple effect clear across the country and beyond.
What is it, exactly, about winter weather that wreaks such havoc for air travel?
Low visibilities, strong crosswinds, slick runways, potential icing -- all of these things spell trouble for pilots, and cause air traffic backlogs. But, as a rule, they aren't phenomenon that airplanes or their crews can't handle. Generally, 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 get bogged down 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. (The deicing guide in my manual is about 20 pages long, with a series of 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 is 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.
There have been several ice-related accidents over the years. In 1991, 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 good news is that the most recent of those accidents was a long time ago. Those were tough lessons to learn, but airliner crashes brought on by icing have become exceptionally rare. Most inflight ice encounters are brief and routine, posing little if any danger; preflight deicing is carefully monitored, and all modern commercial aircraft are equipped with sophisticated deicing equipment for the rare times when things become more serious. Propeller blades, probes 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 any accumulation. These systems use redundant sources and are separated into independently operating zones to keep any one failure from affecting the entire plane.
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.
And 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.
I should call myself lucky, I guess. 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.
Patrick Smith is an airline pilot and the host of www.askthepilot.com.
Portions of this story ran originally on the website Salon, and are excerpted from the author's book, COCKPIT CONFIDENTIAL: EVERYTHING YOU NEED TO KNOW ABOUT AIR TRAVEL
The author is solely responsible for the content.