FAA Flight Instructor Airplane (FIA)Weather and Weather ServicesMedium
A pilot is flying through a layer of stratus clouds composed mostly of small supercooled water droplets. What type of structural ice accumulation is most likely?
- AMixed ice with heavy runback
- BFrost only, with no ice accretion
- CClear ice
- DRime ice
Show answer & explanationAnswer & explanation
Correct answer: D. Rime ice
Rime ice forms when small supercooled water droplets, typical of stratiform clouds, freeze almost instantly on impact, trapping air and creating a rough, milky-white, opaque deposit. Clear ice instead forms from larger droplets, typically in cumuliform clouds or freezing rain.
Why the other options are wrong
- A. Mixed ice is a combination scenario, not the typical result of uniformly small stratiform droplets.
- B. Frost forms from deposition on a cold surface exposed to clear air, not from flying through cloud droplets.
- C. Clear ice results from large supercooled droplets, not small stratiform droplets.
Structural Icing Types
Structural icing forms when supercooled water droplets freeze on an aircraft; droplet size and cloud type determine whether clear, rime, or mixed ice forms.
- Clear ice: large droplets, cumuliform clouds/freezing rain, hard and smooth
- Rime ice: small droplets, stratiform clouds, rough and opaque
- Mixed ice: combination of both types, common in mixed cloud droplet sizes
- All types disrupt airflow and increase weight and drag
Memory trick: Small drops freeze fast and rough — that's RIME; big drops spread smooth and CLEAR.