December 8, 2016

Rules and tips for minimizing icing hazards


Rules and tips for minimizing icing hazards


Winter fast approaches, and its again time to consider the hazards of the icing season.

In previous years I’ve dealt with the specifics of icing, both in terms of weather that produces ice and in terms of its impact on safe flight. If you’ve been following this column for a while, you may feel well versed on the topic already, so I’ve chosen to part with the traditional icing warnings and scare tactics and provide you with rules and tips for avoiding and/or dealing with the hazard.

Back in 1991, I compiled a list for a major report so I’ve referenced that and added a few extras as well.

1) Check the weather thoroughly- get up-to-date information before the flight, i.e. PIREPS.

2) Remove all traces of frost or snow before attempting flight.

3) Don’t remove ice or frost with hot water alone. It will refreeze and may produce a condition worse than prior to the application.

4) Check flight controls for restriction of movement.

5) Before takeoff, insure that anti-icing and de-icing equipment is working correctly.

6) Taxi slowly on wet pavement- avoid puddles when temperature is near freezing.

7) After run-ups in fog or rain, when the temperature is near freezing, check the wings and tail, if possible, for ice in the propeller wash area.

8) Avoid taking off in slush or wet snow. It will freeze in landing gear wells and flap tracks.

9) Exercise the brakes and landing gear after takeoff before final retraction.

10) When climbing out through an icing layer, climb at an airspeed a little faster than normal to avoid the possibility of a stall.

11) When flying in freezing rain conditions (hopefully not by choice), climb into the clouds where the temperatures will be above freezing- unless temperature below is known to be high enough to prevent icing.

12) Use pitot heat when flying in rain, snow, clouds, or suspected icing zones.

13) When flying into clouds above the crest of ridges or mountains, maintain a clearance of four to five thousand feet above the ridges if the temperature within the cloud is below freezing. Icing is more probable over the crests of ridges than over the adjacent valleys.

14) Icing in stratiform clouds is generally restricted to a 3,000-4,000 foot thick layer. Use this information to help guide your exit strategy.

15) When deciding on an icing exit strategy, remember to head for temperatures above freezing or below -20 C. Little moisture exists in air colder than -20 C so the icing potential diminishes rapidly at temperatures below that value.

16) If icing can not be avoided, choose the altitude of least expected icing regardless of aircraft capability.

17) Ice will collect on the propeller more readily at low RPM than at higher RPMs.

18) Ice build-up on radio antennae can not only reduce reception but can break off under the increased weight, either of which makes requesting ATC assistance difficult.

19) Do not wait to activate current de-icing or anti-icing equipment – get it working at the first sign of icing. Older de-icing equipment may operate differently, so follow manufacturer recommendations.

20) If your airplane has wing deicers, do not land with deicers on since they act as airflow spoilers.

21) Avoid full-stall landings with ice on aircraft surfaces- fly in with power.

22) With ice accretion, use the minimum flap setting necessary for a safe landing. Increasing flaps increases downwash and, subsequently, the angle of attack of the horizontal stabilizer.

23) Thinner airfoil leading edges will collect ice faster than thicker ones. That means if there is ice on the wing, there is more on the horizontal stabilizer.

24) If ice is allowed to build on the horizontal stabilizer to the point where that airfoil stalls, recovery is often difficult.

25) Avoid steep bank turns or over maneuvers that increase wing-loading.

26) Watch airspeed when experiencing ice accretion – stall speed increases with the addition of airframe icing.

27) The U.S. experience its worst icing season during winter, while Canada and higher latitudes generally experience the worst icing in the Fall and Spring seasons.

28) Avoid cumuliform clouds that are above the freezing level. Regardless of other conditions, ice can generally be expected in these clouds above the freezing level.

29) Ice accretions on the aircraft increase weight, decrease airfoil effectiveness, and reduce propeller efficiency, all of which can be bad news if you are already underpowered.

30) Water droplets in the free air generally freeze from -10 C to -40 C, and will readily adhere to your airframe if it is 0 C or below. This means that you are rarely safe in a freezing cloud regardless of its temperature.

31) Studies have shown that a mere 1/2 inch of ice on the leading edge of an airfoil can reduce its lift by up to 50 per cent and increase drag by the same amount. That much ice can accrete in less than two minutes.

32) Remember that gas consumption is greater when flying under icing conditions, due to increased drag and the additional power required.

33) If you encounter icing, tell ATC or FSS/FIC about it so others can be alerted to potential hazards.

This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 160 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.