FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesHard
An aircraft flying through a cumulonimbus cloud encounters large supercooled water droplets that freeze slowly upon impact, forming a smooth, hard, transparent layer of ice on the airframe. Which type of structural icing is described, and why is it considered especially hazardous?
- AHoarfrost, because it forms exclusively in stratiform clouds with small droplet sizes
- BFrost, because it forms only on clear, cold nights on parked aircraft
- CClear ice, because it forms rapidly, adheres strongly, and is difficult to remove with deicing boots
- DRime ice, because it is rough and easily removed by deicing boots
Show answer & explanationAnswer & explanation
Correct answer: C. Clear ice, because it forms rapidly, adheres strongly, and is difficult to remove with deicing boots
Clear ice forms when large supercooled water droplets, typical of cumuliform clouds, spread out and freeze slowly, creating a dense, transparent, strongly adherent layer. It is more hazardous than rime ice because it can accumulate rapidly, is harder to see, alters aerodynamic shape significantly, and resists removal by pneumatic deicing boots.
Why the other options are wrong
- A. Hoarfrost is a ground/parked-aircraft phenomenon, not an in-flight icing type from cumuliform clouds.
- B. Frost forms on parked aircraft via sublimation, unrelated to in-flight droplet icing.
- D. Rime ice is rough/opaque and forms from small droplets in stratiform clouds, not this scenario.
Clear Ice
A dense, transparent, and strongly adherent form of structural icing that forms from large supercooled water droplets freezing slowly, typically in cumuliform clouds.
- Forms from large supercooled droplets, common in cumulonimbus clouds
- Denser and harder to remove than rime ice
- Significantly alters airfoil shape, degrading lift and increasing drag
Memory trick: Clear ice = 'glass armor' — see-through but tough to break off.