by Jeffery Taylor – Aviation Consultant –Wisconsin Bureau of Aeronautics
Jeff Taylor
As you walk out to your aircraft, left outside overnight on a trip, you notice some frost on the wings. It doesn’t look like much so your initial reaction is to ignore the frost and get busy with loading, pre-flighting and all the other “little” things we must do before a flight.
You have just missed an opportunity to break a major link in an accident chain.
Frost is insidious. It forms easily, even when the free air temperature might be above freezing; all it needs is some visible moisture and cold air. Many pilots wrongly assume the frost they see is not significant enough to cause a problem, or they don’t even look. Pilots of high-wing aircraft should be especially careful and use a ladder to inspect their wings, since high-wing aircraft account for two-thirds of all general aviation icing takeoff accidents.
Here are some (cold) hard facts:
• When an aircraft manufacturer certifies an aircraft, they assume it’s free of ice contamination. They never test or demonstrate that an aircraft can take off safely with any amount of frost or ice. This makes you a test pilot if you attempt it.
• Even small amounts of frost, snow or ice can increase drag significantly.
• Frost with a roughness similar to medium sandpaper on a wing’s leading edge and upper surface can reduce lift by 30 percent and increase drag by 40 percent.
All surfaces of an aircraft are important. Any amount of frozen contamination creates a significant drag penalty. Don’t forget to check the propeller; the blades are airfoils and your ability to climb depends on their ability to generate thrust. Also, check engine inlets, pitot tubes, static ports, and any angle of attack or stall warning devices.
Can I polish frost?
In the past it was thought the roughness of frost was the problem and it could be mitigated by smoothing or polishing frost instead of removing it. Forget about polishing frost, since at least 15 percent of all small aircraft takeoff icing accidents involved aircraft with polished frost. Take the time to ensure that you clear all contaminants, including polished frost, from wings, stabilizing and control surfaces.
Earlier this year the FAA removed permission to takeoff with polished frost from Part 91, 125 and 135. In the Notice of Proposed Rule Making (NPRM), the FAA identified four alternatives to polishing frost to comply with this rule. They are: (1) using wing covers to prevent frost accumulation on wings, (2) waiting for frost to melt, (3) storing aircraft in heated hangars, and (4) deicing the wing surface.
Snow can also pose a serious threat. While some light snow on the wings may not look threatening, never assume it will blow off during takeoff. While it might blow away, there could be a layer of ice concealed underneath. In addition, it is NOT enough to clean just the leading edge of the wing or only around vortex generators. You need to clear all contaminants from the entire wing surface, including flaps, ailerons, horizontal tail and elevator.
When confronted with frost, snow or ice on an aircraft, the decision is easy. The bottom line is: Make sure your airplane is free of any and all ice contamination prior to takeoff.
