Not only does the frosty precipitation add weight to an aircraft, but it also disrupts the flow of air over the wings and tail and can cause an accident if the circumstances are just right. The FAA and NASA have gone through great lengths to teach pilots about the adverse effects that snow and ice can have on an airplane.
But the most important lesson pilots learned from was from the infamous Air Florida 90 crash in Washington D.C. in 1982. But snow on the wings wasn’t the only problem that aircraft had to deal with. Even more of a factor was the iced up engine probe that is used to display the amount of thrust the airplane was developing during takeoff. The result was that the 737 was producing much less power than the pilots thought, at a time when the snow and short runway made an accurate power setting vital.
Airline deicing has presented a problem long before the jet age arrived. During the twenties while flying passengers in Alaska, my grandfather not only had to make sure the wings were clear of snow and frost, but he had to preheat the engine oil, usually over a stove in the coldest conditions, before putting it back in the preheated motor that was warmed from below using a custom made stove with large blankets wrapped over the engine.
Noel Wien Photo – 1929
While flying to the Eskimo villages outside of Bethel, Alaska, as a new co-pilot I was tasked with using a push broom to get the snow and ice off the top of the wings of the Twin Otter. Usually it was a simple matter of brushing the cold snow from the wing while crawling across the slick aluminum with a push broom. But sometimes the ice was so thick that it was necessary to break it up as gently as possible with the side of handle. It was during one of these mornings, in the cold dark winter, that I thought to myself that Twin Otters were also flown in Hawaii and that I might want to look into that. I managed to capture some of those ice-cold days in a video from back then.
Prior to landing a flying job, I worked for Era as a ramper on the night shift and one of the tasks I was trained to do was to de-ice aircraft in the morning. I learned two lessons from that experience. Firstly, that it was very important not to spray the glycol based de-ice fluid into the wind, and second, that this fluid tasted a lot like maple syrup.
How much does it cost and how long does it last?
The De-ice Process
I have a lot of sympathy today for the certified deicers that clean our airplanes. It’s not an easy job.
Before every ‘snow event’ as our base in Boston calls these storms, crews are assigned and trucks are prepared for the day’s worth of spraying. It’s ultimately up to the pilots when and what type of de-icing fluid is to be used, but the deicers do a good job of planning ahead, especially at our base.
Everything is based on what’s called a ‘holdover time.’ This is the amount of time the FAA says the Type I or Type IV fluid can prevent snow, ice-pellets or freezing rain from adhering to the wings.
Years ago, Type I fluid was really our only option. It’s a de-icing fluid that is used to remove the snow and ice from the airplane. But it’s holdover time was then and still is today rather limited; typically between ten and thirty minutes in duration. So by the time you’re de-iced, if there is any delay departing, which invariably happens during a snow storm as the airport opens and closes runways for clearing, the holdover time is often met.
It is possible to takeoff with an expired holdover time, but it involves an inspection by a pilot from inside the cabin or certified de-icer from the outside within five minutes of departure. This might explain why you’ve seen a pilot come back to check on the wings on occasion before takeoff.
This inspection is very rare today, since we now have Type IV fluid, which is an anti-icing fluid. It’s far more common now to use a two-step process using Type I to remove the snow and Type IV to ensure a long holdover time. Our charts show that Type IV fluid can resist snow for as much as an hour and a half.
While the wings must not have snow or ice adhering to the upper surfaces, the fuselage is usually cleared as well, since the added accumulation can add weight to the aircraft.
The whole process isn’t cheap. Currently Type I fluid costs $3.29 a gallon and Type IV fluid runs a rather steep $5.79. Often these fluids are diluted with up to 50% of the solution made up of warm water, but it’s not uncommon for an airline to spend over $5,000 on a single ice-coated airplane.
Even though it’s so expensive, the effectiveness of Type IV fluid is rather startling-it’s not uncommon to fly for a few hours and still have an oily film sticking to the surface of the airplane after landing.
Occasionally, when the snow fall has slowed a bit, it’s common for the airplane to be de-iced before it’s even boarded, so you won’t encounter the delays from the de-ice process. But the station has to make a determination that the snow won’t be picking up in intensity anytime soon.
If the airplane is to be de-iced after pushing back from the gate with passengers on board, we close off any outside air from entering the cabin during the de-icing to prevent the fluid smell from entering the airplane. A few years back, an Alaska jet had a well publicized incident where de-icing fluid mist filled the airplane while it was getting de-iced. Closing the engine ‘bleed air’ and turning off the air-conditioning ‘packs’ reduces this smell significantly.
Finally, there’s one other anti-icing fluid used to make flying safer and that’s on the runway itself. Airports often add anti-ice fluid in the form of potassium acetate to a runway after plowing the snow in order to keep the braking action fair or better as reported by the airplanes landing there.
The next time you see a de-icer giving your airplane a glycol bath, give ’em a thumbs up. They could use any warm thoughts you might be able to send their way.
Cockpit Chronicles takes you along on some of Kent’s trips as an international co-pilot on the Boeing 757 and 767 based in Boston. Have any questions for Kent? Check out Plane Answers or follow him on Twitter @veryjr.