I consider ice accumulation equivalent to an aircraft being on fire. You have to take immediate action or the consequences will be disastrous. Some pilots rely on the belief that there will be plenty of forewarning before things get serious. Perhaps, but it depends on how fast the ice is accumulating and in some cases it can be very rapid indeed. Usually there will be an increasing loss of performance i.e. loss of climb rate, decreased airspeed, an inability to maintain altitude and so forth. If corrective action is not taken you will not gently descend back to earth, but rather the plane will stall and plummet horrendously out of control. The time to act is at the first onset of ice. You will have to either descend to warmer air, climb out of it if conditions and aircraft performance permit, or do a 180 degree turn to go back to where the air is hopefully still ice-free.
I’ll never forget one of my earlier aircraft accident investigations when a pilot flying a Cessna 210 at cruise altitude in heavy IMC radioed center that he would be returning to the airport because of ice. The plane stalled in the turn and went straight down.
The picture above shows what was left of the plane. It impacted like a lawn dart, sticking out from the snow-covered ground at a 90 degree angle. Three people were killed. The pilot took off where ice would be an obvious factor enroute and didn’t take corrective action until it was too late. The crash scene image has never left my mind and it weighs heavily any time that I have to make a flight in potential icing conditions.
Unlike turbine or jet engine aircraft that bleed hot air to the wings and tail for ice-protection, the average piston general aviation aircraft may, at best, be equipped with pneumatic wing boots, or a “weeping wing” system and maybe a “hot” prop. These systems offer a false sense of security and only permit an opportunity to escape icing conditions. They are not designed to fly in heavy icing conditions continuously.
Even with some wing ice-protection, an unprotected tail section can accumulate a lot of ice and cause the aircraft to stall. Don’t forget that in most general aviation aircraft the horizontal tail surfaces are aerodynamically “down-loaded” in normal flight to counterbalance the weight up at the front of the plane. If the tail stalls, the down-load is lost and the nose pitches steep down. In addition to the tail, ice can accumulate on engine air intakes and antennae causing power loss and lack of radio capability. Do you really want to deal with all this while you are flying in the wet stuff?
Besides better ice-protection systems, turbine-powered aircraft have another advantage that piston-powered aircraft do not have: Lots of excess power. Jets and turbo-prop aircraft can out-climb a lot of stuff that an ice-laden piston airplane cannot. Trying to climb at a few hundred feet per minute increases the exposure time to ice accumulation which in turn degrades performance even further. It is tempting for a pilot to expedite a climb out of icing conditions, using a “best rate” or “best angle” speed, but the increased pitch attitude in the climb may cause an increase in ice accumulation on the bottom of the wing surface as it becomes more exposed to the air stream.
In a discussion of ice, pilots rarely give due consideration to the aircraft’s windshield. Most piston aircraft defrosters are pretty useless when it comes to getting rid of windshield ice. Unless you have a true “anti-ice” (heated or chemical spray) windshield, a frozen-over windshield will have you flying blind when you break out into clear air if the temps are in the freezing range. At cruise altitude you will not see other traffic and if freezing temperatures extend to the surface, trying to find the runway and landing will be an interesting experience with your forward vision obscured.
It is beyond the scope of this article to discuss specific strategies or the legal requirements related to flight in icing conditions, but suffice it to say any possibility of an ice encounter needs to be evaluated in the preflight planning stage. At any point in your planned route, you must be able to articulate an escape plan to non-icing conditions. If you can’t do this with a reasonable degree of certainty then stay on the ground and take a cue from the advertising folk: Got Ice? Just say “No!”
Editor’s Note: This article was written by Ken Steiner prior to his retirement from the United States Aircraft Insurance Group as a Vice-President and Claims Manager. During his career, Ken investigated thousands of aircraft accidents involving small planes, crop dusters, helicopters, corporate aircraft, and airliners. He has been on-site at over 100 fatal aircraft accident investigations. He is currently an Aviation Investigative Consultant and is also a Pilot and Tactical Flight Officer for the San Mateo County Sheriff’s Air Support Unit. He owns a Cessna 182 based at San Carlos and holds ATP and CFI certificates with over 5000 flying hours.