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Winter Icing Conditions

by Patricia Mattson, Reprinted with permission from FAA Aviation News

It's always the small things that sneak up on us and clean our clock. We in the aviation industry are full of hangar stories that run the gamut. One-upmanship is an art when it comes to hanger tales. Most situations discussed are a compilation of small factors that blossom into, in the vernacular of the FAA, occurrences, incidents, or accidents. The outcome is usually dependant on how far things get along before one of the small factors is recognized for the danger it brings.

Since it is still winter, I suppose the first thing we think of is airframe icing. We beat this subject to death each winter and still, folks go out and fly in conditions where icing can occur. How much ice on the airframe is safe for take off? The answer is none. I have seen pilots take a broom or a rag and try to wipe off frost and ice before flight. That really doesn't work, the only real way to keep ice from accumulating is either cover the wings, deice, or hangar the aircraft.

What about un-forecast icing conditions? It happens and when it does there is really only a couple of things that you can do. You can try to find an altitude where it is warmer and ice is not a factor or land the aircraft, especially if the pilot is not fortunate enough to have de-ice or anti-ice systems on the aircraft.

Another wintertime problem is that of ice and water in the fuel system. Engines do not run well on water or ice. Moisture can become trapped in the fuel tanks of aircraft that have been sitting out in the weather. That moisture can be in the form of ice or water and can be trapped in baffles inside the tank. We all check our fuel for color and contaminants after each fueling and before flight. Water in the frozen state would not show up as water and has been known to melt in flight and flow to the fuel lines causing fuel starvation.

In the accident I read about recently the problem just might have been ice in the fuel system. The engine stopped about half an hour into the flight just after the pilot had made rather a steep turn and then leveled off. Shortly after the turn the engine quit. The pilot landed in a field where water was found in the fuel sump.

Another item of concern is ice in the hinges of the aileron, flap and especially the elevator. When ice forms in control surface hinges the control surface cannot be moved. A student pilot recently experienced a trim problem. There was no evidence of any discrepancy with the trim tab after the student landed. I know just how the student struggled to land the aircraft. I had a similar situation myself several years ago and believe me when I say it is nigh on impossible to control an aircraft with a frozen trim tab. It can be done, but you lose a lot of calories in the process not to mention perspiration. The best thing to do is to move the control surfaces periodically during a flight into cold moist air. By moving the control surfaces moisture is not allowed to freeze the hinge solid.

Of course it is best not to fly when the weather is threatening to be cold and wet enough to cause ice, unless you have an aircraft capable of flying in icing conditions. With that said it is safe to say that I have only just touched on some of the winter weather-related subjects that could cause problems.

Fly safely, and please, both you and your airplane, try to keep warm and dry this winter.

Patricia Mattison is an Aviation Safety Inspector and the Aviation Safety Program Manager at the Juneau (AK) Flight Standards District Office.