FAA Aircraft Dispatcher (ADX)MeteorologyMedium
A dispatcher is briefing a flight expected to encounter freezing rain below a warm frontal inversion. Which type of structural icing should be expected in this situation?
- AHoarfrost
- BRime ice
- CFrost
- DClear ice
Show answer & explanationAnswer & explanation
Correct answer: D. Clear ice
Clear ice forms when large supercooled water droplets, such as those found in freezing rain, strike the aircraft and spread out before freezing, forming a smooth, dense, and difficult-to-remove ice layer. This is common below warm frontal inversions where freezing rain occurs.
Why the other options are wrong
- A. Hoarfrost is another term describing the same ground-surface phenomenon as frost, not applicable to in-flight icing.
- B. Rime ice forms from small supercooled droplets that freeze instantly, typically in stratiform clouds, producing a rough, opaque, brittle ice.
- C. Frost forms from sublimation of water vapor on a surface below freezing while on the ground, not from freezing rain in flight.
Clear (Glaze) Ice
A type of structural icing formed by large supercooled water droplets, such as freezing rain, that spread out and freeze slowly into a smooth, dense, transparent layer that adheres strongly to aircraft surfaces.
- Forms from large supercooled droplets, common in freezing rain and cumuliform clouds
- Smooth, hard, transparent, and difficult to remove
- Most hazardous icing type due to weight and effect on aerodynamics
Memory trick: 'Clear ice is Crystal-clear and Clingy, Rime ice is Rough and Rigid.'