Section I: Equipment and Environment
Part IV, Chapter 11: Problems with Frost, Snow, and Ice
There is a mystery, a strangeness, about it. Every winter the same scenario repeats itself over and over again without fail or the slightest respite. An airplane with frost, snow, or ice contaminating its wing and tail surfaces taxis to the runway and moves into position. Power is applied, the plane lifts lumberingly into the air, staggers through ground-effect, stalls, and spins in. Or, alternatively, mushes into the trees off the end of the runway. Gets "rolled in a ball" as they say in the business.
This scenario is not in the least confined to light airplanes and amateur pilots: in 1987, 28 people were killed and another 28 seriously injured at Denver after a crash of a Continental Airlines DC-9-14 because of snow and ice on the wings. And two years later at Dryden, Air Ontario did no better, with a death toll of 24 of their passengers.
Witnesses reported "a considerable amount of snow and ice" on the wings of Air Ontario's F-28 during the takeoff roll; the pilots were offered deicing services prior to takeoff but "declined." As for the Continental pilots, they apparently sat unconcerned in a nice warm cabin in a wet snowfall (classified as "moderate") at the runway threshold for 27 minutes after having the plane deiced, even though the DC-9-14 is notorious for its inability to withstand even 1/32 of an inch of wing contamination, and Company policy demands at least a visual check of the wings prior to takeoff if the delay has been longer than 20 minutes.
What is going on? What could be preventing these pilots from responding to this situation, especially when the aerodynamics of the situation are so clear, so terribly unambiguous?
If anyone who reads this has the answer, I would like to learn what it is, though I have a sneaky hunch this is a problem for the boys (and girls) who specialize in abnormal psychology. Surely it can't just be a product of plain (plane?) stupidity.
As for those who know better, their problem is simply deciding which of the many techniques available is the best to use under the circumstances.
Prevention
Wing covers
Wing covers, in the bush or on the ramp, are your major line of defense, and, like many simple and obvious remedies, they work surprisingly well.
These covers, which are now made of nylon -- in ye olden times, they were made of stiff, heavy canvas and were quite bulky -- are designed to slip over the top surface of the wings and fasten underneath with either bungee cords, nylon straps, or ropes (see illustrations 18 and 27).
The usual procedure is to place them on the airplane after the last flight of the day, while tying it down. Then, on the following day, just prior to flight, they are removed. When not on the airplane, they are stored in a small stuff-bag which is left at home base, unless it is anticipated that the airplane will be away for the night (see Chapter 24).
Like anything else, though, wing covers are not a perfect solution to all problems and here the main one is a snowstorm that turns to slush or rain and then freezes. This type of situation usually produces the following problems:
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Soaked wing covers that are now frozen to the wings.
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A thick layer of rime ice on the top surface of the wing covers, tail, and the rest of the airplane's structure
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Accumulations of ice on the bottom rear edges of the control surfaces caused by water building up and then freezing on the underside of the wing covers where the straps attach. This ice, if allowed to remain, can cause control flutter which is very dangerous; it must be removed prior to flight.
Out in the remote bush, far from a heated hangar, these problems are not nearly as insurmountable as they appear. A little methodical effort will soon put things right once again:
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Wings. The wing covers will peel off the wings leaving behind a thin coating of ice which will usually be of little serious consequence since it generally follows closely the curvature of the wings, therefore disrupting the airflow only in subtle ways. Once in the air you can seek out a warm layer above the inversion, and, if found, melt off this coating.
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Bottom rear edges of the control surfaces. Here you will have to remove it by hand, usually not all that much of a job.
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Horizontal tail. Here, too, you will have to manually remove the contamination, and this is done by rubbing it loose with your gloved hands, or a piece of folded rope. Crude, but it works, and if done carefully it will not damage the paint. With fabric airplanes the flexing of the fabric will easily break the ice loose; with metal airplanes it is slightly more of a job.
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Prop and spinner. The propeller, an airfoil, will have to be carefully cleaned. The easiest method is to take a piece of wood like an old axe or broom handle and carefully rub it up and down the blades until all ice has been removed.
The spinner must also be checked, for often melting snow can collect in it creating an out-of-balance condition. It helps to align the prop horizontally prior to the storm -- or, if leaving it partially-vertical, cover it with a plastic garbage bag -- as the main route of this moisture is down the blade when the prop is left in its natural position after shutting down the engine.
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Windshield. This works the same way as the wings. Peeling off the cover (described below) leaves a thin layer of ice. Usually this takes the form of streaks and patches, leaving a spot or two where the visibility is good enough to allow takeoff. Once in the air, a few minutes of defroster action will clean it.
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Hinges, moving parts, and the pitot/static system. The rest of your airplane must be gone over carefully to make sure there is no ice that could interfere with the proper operation of any system or control. If found, it will have to be removed by hand.
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Wing covers. The final step is to clean these covers; this you will do also for the engine, windshield, and tail covers, which will be described next. The best way to do this is to remove as much snow and ice as possible outside, and then hang them in a warm building to thaw and dry. City dwellers can just dump them in a clothes dryer, turn it on, and go about their business; when they get back after their flight, their covers will be nice and dry, waiting to be used once again.
High winds, as well, cause problems with wing covers that are not properly installed. Bungee cords and metal hooks used for convenience to attach the covers loosen when temperature variations and age manage to cause them to stretch and become inelastic. Lost wing covers, damaged paint and fabric, and, sometimes, even broken windows -- from the hooks banging around during a storm -- result.
The best way to forestall these problems is to throw away the bungee cords and hooks and replace them with 1/4 inch nylon cords, or one-inch nylon straps -- the soft type you can tie, like those Cessna uses with its cargo nets. In this way, you will be able to carefully adjust the tension of each cord to its optimum setting without hooks or buckles, and the wing covers will always fit properly.
In my experience, wing covers fastened this way will stay in place in winds officially clocked in excess of 80 knots. As an added advantage for the Super Cub, they will act as control locks for the flaps and ailerons.
It takes about ten minutes to install a set of wing covers properly. Like tying your airplane down correctly so it will ride out a serious storm, the regular use of wing covers is well worth while.
Tail Covers
Tail covers function like wing covers but are rarely used in the bush because of the time and effort involved in putting them on and taking them off. I use them in freezing rain, but rarely otherwise.
Windshield covers
Windshield covers are used just like wing covers, are made of the same material, and serve the same purpose. However, during windstorms, it's better not to use them -- they can scratch the windshield if allowed to rub against it.
As with wing covers, replacement of the bungee cords and hooks with nylon cords or straps is advised.
Engine covers
Engine covers are made of a nylon shell padded on the inside with a synthetic insulation. They are primarily used to retain heat in the engine compartment during short ground waits between flights, and while preheating the engine (see the next chapter).
A secondary use is to keep snow and ice off the cowling and out of the engine compartment. Like the wing covers, the engine cover does a good job of keeping a surface clean, but once the wind gets above 60 knots or so, blowing snow will work its way through the overlapping edges and some engine compartment contamination will occur. Usually, preheating will resolve this problem without difficulty if you are using a combustion method, which frequently is the case in remote areas.
Hangars
Of course, all these considerations are moot if you have the luxury of a hangar and the airplane is on wheels or wheel-skis -- although heated hangars have their own problems, described below. But there are few hangars in the bush, and many airplanes on board-skis. So you do the best you can with what you have, and I must confess that in over 22 years of flying Alaska and Northern Canada the only time any of my airplanes ever saw the inside of a hangar was when they were in Anchorage for maintenance.
Cure
Based far from the support of civilization, bush pilots have a tendency to be far more careful and methodical than city pilots in the way they secure their airplanes after the last flight of the day. As a result, they rarely have to contend with contamination problems -- except for the previously mentioned freezing rain/snow situation. However, for pilots visiting town who get caught in an unexpected snow storm, or who live in town but somehow neglect to put on their wing covers, the following techniques can prove useful.
Hangars
If your snow or ice-contamination problem occurs at an airport where there are maintenance shops available, a bad case is easily -- but expensively -- solved by shoving the airplane into a heated hangar so it can thaw out.
However, there is one major caveat concerning the use of heated hangars to defrost cold-soaked ice and snow-covered airplanes: they must be left in the hangar not only long enough for all the snow and ice to melt off, but also long enough to get completely dry both inside and out. If this is not done, you risk exposing yourself to the following problems:
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Control-flutter caused by refreezing melted snow and ice that has collected but not completely drained from the elevator, ailerons, etc.
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Control binding caused by the freezing of wet pulleys, etc.
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Frozen condensation in the fuel thawing, and then refreezing, so as to block fuel flow. The tanks and all sumps should be well drained each time the airplane spends more than a couple of hours in above-freezing temperatures during the winter. When temperatures are below freezing, it is generally a poor idea to drain the sumps because they will often fail to reseal properly leaving one with a fuel leak.
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With the Super Cub, snow is often blown into the fuselage through the stabilizer adjustment slot, and, in serious cases, this can form a block of drifted snow stretching from the battery-box to the bellcranks and upper control cables. If it is allowed to partially thaw and then refreeze, it could not only interfere with control movements but also place a serious weight at the very aft-end of the c.g. arm.
A heated hangar is nice, but it must be used carefully and intelligently during cold weather.
Hot water
Using hot water to defrost an airplane can get one in hot water. I will sometimes use it on the windshield if conditions are bad, but nowhere else. The reason should be obvious.
Broom
When the snow is dry, or wet with temperatures above freezing, using a broom to remove the snow works very well. In the bush, even with wing covers installed, it is standard practice to brush off all the snow you can prior to removing them. A good broom -- with soft bristles that will not damage the airplane's paint -- can be considered part of the winter equipment list for all remote-area bush pilots.
Rope
The following technique, while approaching the Mickey Mouse level, can be used to smooth down heavy frost so the airplane will fly. It should not be used except in emergencies, when you get caught by an unexpected frost in some remote area and there are no other options available.
What you do is take one of your tiedown ropes, pass it over a wing, and then work it back and forth using its abrasive characteristics to wear down the frost. It is more a polishing job than a removal job, and the most important part of the wing is the leading edge. Well polished -- on the airplanes used for bush flying -- the wing curvature will be correct enough to allow for flight, and a few hours in the air will finish the job. A word of advice: keep the .c.g. in the mid-range and the load light until the wings are completely clean, and do not try to horse the airplane off the ground early on takeoff.
Chemicals
These have no place in the bush pilot's world, and I have never seen or heard of anyone using glycol or automotive deicer. The cost of purchasing it, transporting it into the bush, and using it on a daily basis makes as much sense as hauling out an electric generator to operate an electric carving knife or can opener. This stuff is best left to the airlines, with their trucks, spraying devices, and teams of workers.
