FAA Commercial Pilot Airplane (CAX)WeatherHard
A pilot is flying at 8,000 feet MSL and notices the outside air temperature is +3°C, while the air is saturated with visible moisture. What type of structural icing condition is most likely to form on the aircraft?
- ARime ice, due to the colder temperatures at altitude causing rapid freezing of small droplets.
- BMixed ice, as the conditions suggest a combination of freezing and non-freezing precipitation.
- CNo structural icing, as the temperature is above freezing.
- DClear ice, as the temperature is above freezing, allowing supercooled water to spread before freezing.
Show answer & explanationAnswer & explanation
Correct answer: D. Clear ice, as the temperature is above freezing, allowing supercooled water to spread before freezing.
Structural icing can occur at temperatures above 0°C (up to +2°C or +3°C) when supercooled large water droplets are present. In this scenario, the +3°C OAT with visible moisture indicates that large supercooled droplets are likely. These droplets freeze slowly and spread out before freezing, leading to the formation of clear ice.
Why the other options are wrong
- A. Rime ice forms at colder temperatures (typically 0°C to -15°C) from smaller supercooled droplets that freeze instantly upon impact, not at +3°C.
- B. Mixed ice is a combination of rime and clear ice. While possible, the given conditions (+3°C, visible moisture) are more indicative of clear ice formation due to the slower freezing of larger droplets at warmer supercooled temperatures.
- C. Structural icing can occur at temperatures slightly above 0°C (up to +2°C or +3°C) due to supercooled large water droplets and the latent heat of fusion.
Clear Ice Formation Conditions
Clear ice forms when supercooled large water droplets (SLD) strike an aircraft surface and freeze slowly, spreading out to form a smooth, clear, and tenacious layer of ice.
- Typically occurs at temperatures between 0°C and -10°C, but can form up to +2°C or +3°C.
- Associated with cumuliform clouds, freezing rain, and freezing drizzle.
- Most dangerous type of icing due to its rapid accumulation and difficulty of removal.
Memory trick: Ice forms when water is supercooled, even if the air feels slightly warm.