FAA Private Pilot Helicopter (PRH)WeatherMedium
A helicopter pilot encounters visible moisture with the outside air temperature at −8°C during a flight. Large, supercooled water droplets are present. What type of structural icing is most likely to form, and why is it considered hazardous?
- AFrost, because it only forms on the ground during cold, clear nights
- BClear ice, because the large droplets spread out before freezing, forming a smooth, dense, hard-to-remove layer
- CRime ice, because it forms slowly and is easy to see and remove
- DHoarfrost, because it forms exclusively in the mature stage of thunderstorms
Show answer & explanationAnswer & explanation
Correct answer: B. Clear ice, because the large droplets spread out before freezing, forming a smooth, dense, hard-to-remove layer
Clear ice forms when large supercooled water droplets strike the airframe and spread out before freezing, creating a smooth, transparent, dense layer that adheres strongly and is difficult to remove, significantly altering aerodynamic surfaces and adding weight.
Why the other options are wrong
- A. Frost forms on parked aircraft from sublimation, not from in-flight icing with visible moisture.
- C. Rime ice forms from small droplets that freeze instantly, creating a rough, opaque, brittle deposit — not from large supercooled droplets.
- D. Hoarfrost is unrelated to thunderstorm stages and forms on cold surfaces exposed to humid air.
Structural Icing Types
Structural icing forms when an aircraft flies through visible moisture at freezing temperatures; the type depends on droplet size and freezing rate.
- Clear ice: large droplets, spreads before freezing, smooth/dense/hard to remove
- Rime ice: small droplets, freezes instantly, rough/milky/brittle
- Mixed ice: combination of clear and rime characteristics
- Icing requires visible moisture and temperatures at or below freezing
Memory trick: Clear ice = 'clear and Cruel' (smooth, hard, dangerous); Rime = 'Rough and Removable'