FAA Aircraft Dispatcher (ADX)MeteorologyEasy
A PIREP from a flight in stratiform clouds at -12°C describes ice accumulating as a rough, opaque, milky-white deposit that formed rapidly on the leading edges of the wings. Which type of icing does this describe?
- AClear (glaze) ice
- BRime ice
- CMixed ice
- DFrost
Show answer & explanationAnswer & explanation
Correct answer: B. Rime ice
Rime ice forms from small supercooled water droplets that freeze almost instantly on contact, trapping air and producing a rough, opaque, milky-white appearance typically found in stratiform clouds. Clear ice, by contrast, forms from larger droplets that spread before freezing, producing a smooth, transparent, glassy coating.
Why the other options are wrong
- A. Clear ice is smooth, transparent, and typically forms from larger supercooled droplets in cumuliform clouds or freezing rain.
- C. Mixed ice combines rough and smooth characteristics from a mix of droplet sizes.
- D. Frost forms from direct deposition of water vapor on a surface below freezing, not from droplet impact in flight.
Rime Ice
A rough, opaque, milky-white ice formation caused by small supercooled water droplets freezing instantly on impact, common in stratiform clouds at colder temperatures.
- Freezes rapidly, trapping air pockets (opaque appearance)
- Common in stratus clouds and colder temperature ranges
- Brittle and relatively easy to remove compared to clear ice
Memory trick: Rime ice is 'rough and white like a snow-crusted rock' — instant freeze, opaque look.