Icing, Mountain Waves and Cold-Weather Hazards
What the exam tests
This domain tests airframe and carburettor icing, mountain-wave hazards and cold-weather operations.
Core rules
- Airframe icing occurs in visible moisture at temperatures from about 0°C to -20°C, with the greatest risk in supercooled water. Clear ice is heavy and irregular; rime is rough and milky; mixed ice combines both.
- Carburettor icing can occur at outside temperatures well above freezing, especially with high humidity; use carburettor heat as prescribed.
- Mountain waves form when stable wind crosses a ridge; indicators include lenticular clouds, rotor clouds and strong downdrafts on the lee side. Expect severe turbulence and altimeter errors.
- Cold-weather hazards include freezing rain, snow, whiteout, runway contamination and reduced braking action.
Worked example
Surface temperature is 2°C and the freezing level is 1,500 ft, with cloud above. Climbing in cloud through the 0°C to -10°C layer exposes the airframe to supercooled droplets, so icing is likely. The reasoning combines visible moisture, a temperature band favourable to supercooled water and a climb through it.
Traps
Assuming no icing above freezing level; confusing clear and rime ice; ignoring carburettor icing in warm humid conditions; flying downwind of a ridge without allowing for mountain-wave downdrafts.