A pilot receives a PIREP reporting freezing rain at 6,000 feet. What is the most significant hazard associated with this report compared to typical rime or mixed icing?
- AFreezing rain is associated exclusively with stable air and poses less risk than icing in cumulus clouds
- BFreezing rain only occurs above the freezing level and poses no threat to aircraft at cruise altitude
- CFreezing rain typically only affects the leading edges of the wings and is easily removed by deice boots
- DFreezing rain indicates supercooled large droplets that can form clear ice rapidly beyond the protected areas and deicing capability of the aircraft
Show answer & explanationAnswer & explanation
Correct answer: D. Freezing rain indicates supercooled large droplets that can form clear ice rapidly beyond the protected areas and deicing capability of the aircraft
Freezing rain is produced by supercooled large droplets (SLD) that remain liquid until striking a surface, then freeze into clear ice. These larger droplets can extend icing beyond the protected surfaces (behind deice boots) and can overwhelm an aircraft's ice protection systems rapidly, making it one of the most hazardous icing conditions.
Why the other options are wrong
- A. Freezing rain is unrelated to cumulus buildups; it forms in stratiform precipitation with a temperature inversion aloft.
- B. Freezing rain occurs below a warm layer aloft and above a subfreezing layer near the surface, and it is a serious threat at those altitudes.
- C. This is backwards; freezing rain often ices areas beyond boot-protected surfaces.
Supercooled Large Droplets (SLD)/Freezing Rain
Freezing rain forms when rain falls through a subfreezing layer near the surface after originating above a warm layer aloft, creating supercooled large droplets that freeze on contact and form clear ice rapidly.
- Requires a temperature inversion: warm layer aloft, cold layer below
- Produces clear ice which is dense and hard to remove
- Can extend icing beyond the aircraft's normal ice-protected surfaces
- One of the most hazardous icing conditions for aircraft, especially non-SLD-certified aircraft
Memory trick: Freezing rain = 'Fast, Far-reaching, Fierce' ice