This post was originally published on snow.news, my free Substack on snow science and the state of the snowpack.
If you fly during wintry weather, your plane may need to make a pitstop before takeoff so it can go through a critical step that prevents the aircraft from crashing.
Deicing is the process by which ice and snow are removed from an aircraft’s surface so that the frozen contaminants don’t mess with the plane’s aerodynamics.
On a flight last week out of Durango, we went through the procedure and made it safely to Denver without slamming into terra firma. I was also relieved that the residue of the deicing fluid only obscured the view from my window during the first few minutes of the flight (I’m a little obsessed with aerial photography and find the window seat the only redeeming quality of air travel).
One of the most infamous airline tragedies associated with ice and winter weather was the January 13, 1982, crash of Air Florida Flight 90 into the Potomac River during a heavy snowstorm as the plane departed Washington National Airport (now called Ronald Reagan Washington National Airport). All but four of the 74 passengers died, as did four of five crew members and four motorists on the 14th Street Bridge.
“Loss of control was determined to be due to reduction in aerodynamic lift resulting from ice and snow that had accumulated on the airplane’s wings during prolonged ground operation at National Airport,” according to the Federal Aviation Administration. “Even small amounts of frost, ice, or snow can have catastrophic effects on airplane performance.”
Deicing was used prior to Flight 90’s takeoff, but the nozzle delivered a solution that was too weak, and too much time elapsed before the plane took off, allowing frozen material to accumulate on the wings.
The crew, which had limited experience flying in winter weather, turned off an engine anti-icing measure, and a sensor was apparently plugged with ice, leading to erroneous data on the engine’s thrust. It was so snowy at the airport that the plane had trouble pushing back from the gate and needed a tug equipped with tire chains to help it maneuver.
The tragedy in the nation’s capital changed winter aviation practices at home and abroad, as the FAA notes:
The crash of Air Florida Flight 90 was a major catalyst for significant advances in the safety of winter weather operations, particularly in the area of airplane deicing technology and procedures. Numerous initiatives were undertaken in order to better understand the properties of deicing materials, techniques for their application, and related training programs.
The D.C. crash was hardly the first nor the last case of ice and snow causing planes to fall from the sky. Wikipedia lists no fewer than 46 cases of frozen water causing airliner accidents around the world.
I’ll spare you a treatise on the various types of treatments, but there’s a distinction between deicing fluids, which remove the frozen contaminants, and anti-icing solutions, which prevent subsequent freeze-up before takeoff.
Heated propylene glycol, which lowers the freezing point of water, is the most common chemical used, but it’s also mixed with other ingredients, such as thickening agents, corrosion inhibitors, and dyes that allow crews to see what surfaces have been treated.
For more on how planes are deiced, check out this video from the Wall Street Journal:
Below is another take from Southwest Airlines, told through the voices of the good folks who apply the fluids, sometimes while sitting in an open-air bucket and exposed to the elements.
