FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesMedium
A pilot flying through a cloud with large supercooled water droplets at an OAT of -4°C is most likely to accumulate which type of structural ice?
- ARime ice, forming a rough opaque layer
- BMixed ice, forming small pellets that fall off
- CFrost, forming a thin white coating
- DClear ice, forming a smooth, transparent layer that is difficult to remove
Show answer & explanationAnswer & explanation
Correct answer: D. Clear ice, forming a smooth, transparent layer that is difficult to remove
Clear ice forms when large supercooled water droplets strike the airframe near freezing temperatures (typically 0°C to -10°C) and spread out before freezing, creating a smooth, transparent, dense layer that is difficult to remove and can significantly alter aerodynamics.
Why the other options are wrong
- A. Rime ice typically forms from small supercooled droplets at colder temperatures, freezing instantly and trapping air, producing a rough, opaque appearance.
- B. Mixed ice is a combination of clear and rime ice appearance, not simply pellets that fall off.
- C. Frost forms on a cold surface from direct deposition of water vapor, not from droplets impacting in flight.
Clear Ice
A smooth, transparent, dense ice formation caused by large supercooled water droplets freezing slowly on the airframe near 0°C to -10°C.
- Forms from large supercooled droplets (e.g., freezing rain or cumuliform clouds)
- Smooth, transparent, and adheres strongly, hard to remove
- Most hazardous ice type due to weight and aerodynamic disruption
Memory trick: Clear ice is 'clear and near freezing'; rime is 'rough and really cold'.