FAA Instrument Flight Instructor (FII)WeatherEasy
A pilot flying through a layer of stratiform clouds at -8°C notices ice forming on the wing leading edges. The ice is rough, milky white, and opaque. Which type of icing is this, and why does it form this way in this cloud type?
- ARime ice, because small supercooled droplets freeze instantly on contact
- BFrost, because sublimation occurs on the cold metal surface
- CMixed ice, because both large and small droplets are present
- DClear ice, because large supercooled droplets spread before freezing
Show answer & explanationAnswer & explanation
Correct answer: A. Rime ice, because small supercooled droplets freeze instantly on contact
Stratiform clouds typically contain small supercooled water droplets. These droplets freeze almost instantly upon striking the aircraft surface, trapping air and creating a rough, opaque, milky-white deposit known as rime ice.
Why the other options are wrong
- B. Frost forms from direct deposition of water vapor, not from droplet impact in flight.
- C. Mixed ice requires both droplet sizes, not typical of uniform stratus layers.
- D. Clear ice forms from large droplets typically found in cumuliform clouds, not stratiform.
Rime Ice
A rough, milky, opaque ice formation caused by small supercooled water droplets freezing instantly on impact, typically in stratiform clouds.
- Common in stable stratus clouds with small droplets
- Freezes quickly, trapping air bubbles for a rough opaque look
- Less hazardous aerodynamically than clear ice but still degrades performance
Memory trick: Rime is rough and rapid; Clear is smooth and slow.