Noel Wien Photo - 1929

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.