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.
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