FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesMedium
A pilot flying through a layer of stratiform clouds at -8°C notices ice forming on the wing leading edge that appears rough, milky white, and opaque. This ice most likely formed due to which process?
- ARapid freezing of small supercooled water droplets typical of stratiform clouds
- BFreezing rain falling through a subfreezing surface layer
- CSublimation of water vapor directly to ice on the airframe
- DSlow freezing of large supercooled droplets that spread before freezing
Show answer & explanationAnswer & explanation
Correct answer: A. Rapid freezing of small supercooled water droplets typical of stratiform clouds
Rime ice forms when small supercooled water droplets, typical of stratiform clouds, freeze almost instantly on contact with the aircraft surface, trapping air and producing a rough, opaque, milky-white appearance. Clear ice, by contrast, forms from larger droplets that spread before freezing, producing a smooth, transparent coating.
Why the other options are wrong
- B. Freezing rain occurs near the surface in specific temperature inversion setups, not typical stratiform cloud icing.
- C. Sublimation frost forms differently and is not typically associated with in-flight structural icing of this type.
- D. This describes the formation of clear ice, not rime ice.
Rime Ice
A rough, opaque, milky-white ice that forms when small supercooled water droplets freeze rapidly on contact with an aircraft surface, common in stratiform clouds.
- Forms from small droplets
- Rapid freezing traps air, giving rough texture
- Common in stratiform clouds at colder temperatures
Memory trick: Rime is rough and rapid; clear is smooth and slow.