FAA Commercial Pilot Airplane (CAX)WeatherHard
A pilot is flying at 7,000 feet MSL and notices the outside air temperature is 0°C. The aircraft is accumulating clear ice rapidly. What is the most likely cause of this severe icing condition?
- ASupercooled large droplets (SLD) that spread across the airfoil before freezing.
- BFreezing rain from an inversion below the aircraft.
- CSupercooled water droplets with a small diameter, freezing instantly on impact.
- DSnow pellets and ice crystals impacting the airframe.
Show answer & explanationAnswer & explanation
Correct answer: A. Supercooled large droplets (SLD) that spread across the airfoil before freezing.
Clear ice forms when supercooled water droplets are large enough that they do not freeze instantly upon impact with the aircraft. Instead, they spread out over the airfoil surface before slowly freezing, creating a smooth, transparent, and often very tenacious layer of ice. This is characteristic of Supercooled Large Droplets (SLD) and is a severe icing hazard.
Why the other options are wrong
- B. Freezing rain forms below an inversion and would be encountered if descending into it, not necessarily at 7,000 feet with 0°C causing clear ice accumulation from cloud droplets.
- C. Small supercooled droplets typically form rime ice, which is opaque and brittle.
- D. Snow pellets and ice crystals typically cause trace or light mixed icing, not rapid clear ice.
Clear Ice Formation
Clear ice forms from supercooled large droplets (SLD) that impact an aircraft and spread across the airfoil surface before freezing, creating a smooth, transparent, and often significant ice accumulation.
- Forms from Supercooled Large Droplets (SLD).
- Droplets spread before freezing.
- Results in a smooth, transparent ice layer.
- Can be very tenacious and difficult to remove.
- Often forms in temperatures near 0°C to -10°C.
Memory trick: Clear ice's secret: SLD's spread, a frozen sheet.