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Aircraft must be clean of any surface contamination

 

Most of us don’t fly after we discover snow, ice or frost on our aircraft. It is just too much work to clean it off. But then we wake up one morning and it is a gorgeous cold sunny day and the "gotta go flying" bug hits. We get to the bird and it is frosted like a wedding cake.

Canadian Aviation Regulations (CARs) states that all critical surfaces of an aircraft must be clean of any surface contamination – the clean aircraft concept. The critical surfaces of an aircraft are the wings, control surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilizing surface.

In the case of an aircraft with rear mounted engines, the upper surface of the fuselage is also a critical surface.

According to A.I.M. AIR Flight Operations 2.12.2 (d), "Test data indicate frost, ice or snow formations having a thickness and surface roughness similar to medium or course sandpaper on the leading edge and upper surface of a wing can reduce lift by as much as 30 per cent and increase drag by 40 per cent."

As well as affecting lift and drag, critical surface contamination can reduce thrust, increase stall speed, alter stall and handling characteristics and cause trim changes.

I think this is trying to tell us that taking-off with a contaminated aircraft is bad. So now if we want to fly, we have to work. Just a minute, maybe we don’t have to work after all. Do we know someone who has a hangar and some heat?

He’s not here today. Let’s go for coffee and let the sun take care of it. We’ll just position the aircraft so that the sun hits most of the upper surfaces. Even on cold days, the skin will warm enough so that the frost will melt off. The aircraft may have to be moved after a while to allow the sun to get at areas of the aircraft that were shaded by other parts of the aircraft.

De-icing fluids like isoproponol work well, especially if heated. A 50/50 mixture of de-icing fluid and water works even better when heated as the water reduces the viscosity of the de-icing fluid and allows for better penetration of the contaminant and for better run off. A combination of this and the sun will clean of the aircraft fairly quickly.

Don’t rush the job. It takes a little time for the de-icing fluid to penetrate all of the way to the skin. Take care not to spray directly onto any of the aircraft windows, or the pitot or static ports, as damage may occur.

Clean as much of the snow off the aircraft as possible before de-icing. Slush formed by the melted snow has a tendency to run down between the horizontal surfaces and the flaps, ailerons and elevators. The slush may re-freeze and jam a control surface. Make sure these areas are also clear of contamination before flight.

Any cloud at all and there is no sun to work with. If we still want to go flying, we will have to work for it. A rope rubbed gently over an aircraft surface will loosen a lot of the frost. A broom, a cloth or a glove can then wipe the surface clean down to the paint.

Gentle use of a plastic scraper will clean off difficult ice or frost, and in a pinch, a credit card will do. Plastic scrapers can damage the paint and de-ice boots if care is not taken.

Hot water as a de-icing method appears to work well. However, the hot water may leave a thin, hard to see layer of ice on the wing surface. It may be necessary to feel for ice with your bare fingers to insure the wing is clean. The water may also form ice around hinges, control rods and cables, which may cause control surfaces to jam.

High wing aircraft and float aircraft are very difficult to completely de-ice. There is a tendency to become frustrated and think a partial job is adequate.

Even after frost has been removed from the aircraft, we must keep an eye on the aircraft surfaces as the atmospheric conditions that caused the frost may not have changed and the frost may reform. A visual check just before take-off is important, and if there is any doubt, the take-off should be aborted.

If we discover snow or ice on our bird, most of us will just sweep off the snow to see if the wing will come clean. If it does, great, if not, we’ll go home. A warm day will do the work for us.

Those of us who really want to go flying may have to deal with a thin layer of frost or ice under the snow that may not even be visible to the eye. Running the fingers over a surface may detect contamination that may not be seen. This contamination must be eliminated before take-off as well.

We tend to forget about the propeller and vertical stabilizer when checking for frost or ice. We forget they are lifting or stabilizing surfaces.

The best solution is to prevent snow, frost or ice from forming on the aircraft in the first place. A hangar is best, but any shelter will do. It doesn’t have to be enclosed.

Wing and tail covers designed for each make and model of aircraft are available from several sources. They are not very expensive and work well. If professionally made wing and tail covers are outside the budget, cheap tarps can be used. They won’t fit as well as a professionally designed covers, but they work.

Be careful about putting covers over a wet wing. The water can freeze to clear ice under the cover and can be difficult to detect. This can also happen if the cover is poorly fitted or has tears.

Anytime a cover is removed from a surface, the surface should be checked visually and with our bare fingers to make sure the cover was effectively doing its job.

Aircraft should perform very well on cold days. If we are not lifting off when we think we should be, we should not try to pull the aircraft into the air. We should abort the take-off and inspect the wings. If we do get airborne with contaminated wings, we may not be able to climb out of ground effect.

The clean aircraft concept means no snow, frost or ice on any critical aircraft surface.

Flying is fun. Let’s keep it that way.

Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently flies air charters. He still freelances as a flying instructor and seminar facilitator. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.

Got an aviation safety story to tell? Dale Nielsen would like to hear from pilots who have educational aviation experiences to relate. Excerpts from these stories will be used in upcoming safety articles. Dale can be contacted via e-mail: dale@flighttrainingmanuals.com.