FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesHard
A pilot is planning a flight and reviews a PIREP indicating the freezing level at 6,000 feet, with cloud tops reported at 10,000 feet and an OAT of -8°C at that altitude. Based on this information, what is the most significant hazard between 6,000 and 10,000 feet?
- AClear air turbulence due to strong wind shear
- BConvective turbulence due to unstable air
- CVolcanic ash contamination affecting engine performance
- DStructural icing due to visible moisture at temperatures below freezing
Show answer & explanationAnswer & explanation
Correct answer: D. Structural icing due to visible moisture at temperatures below freezing
Structural icing requires visible moisture and temperatures at or below freezing. Since the freezing level is at 6,000 feet and clouds extend to 10,000 feet with temperatures well below freezing (-8°C), the entire cloud layer above the freezing level presents a significant icing hazard for any aircraft flying through it.
Why the other options are wrong
- A. There is no mention of wind shear in the scenario; the key hazard identified is temperature and moisture related.
- B. No information suggests instability or convective activity; the scenario describes a stratiform cloud layer with icing potential.
- C. There is no indication of volcanic activity in this scenario; the hazard described is icing, not ash contamination.
Icing Hazard Assessment
Structural icing occurs when an aircraft flies through visible moisture (clouds, rain) at temperatures at or below freezing.
- Requires both visible moisture and sub-freezing temperatures
- Freezing level marks the base of potential icing in clouds above it
- PIREPs and forecast freezing levels help pilots identify icing layers
Memory trick: Clouds + cold = ice — check the freezing level first.