Under which conditions is engine ice in flight most likely to form?

Under which conditions is engine ice in flight most likely to form?

• A. Only in clear dry air
• B. During temperatures above freezing with high humidity
• C. When there is SWD, or any precipitation near or below freezing
• D. In temperatures well above freezing with no moisture

Answer: (C)

Engine ice forms when moisture is present in the air at or near freezing and the engine surfaces are cold enough to freeze that moisture on contact. In flight, visible moisture such as clouds, fog with liquid water, rain, drizzle, or snow, especially near or below freezing, provides liquid droplets that can strike the engine and freeze quickly on impact. Supercooled droplets remain liquid down to subfreezing temperatures and then freeze upon hitting the hot engine surfaces, creating ice buildup on inlets and surrounding areas. If the air is dry, or if temperatures are well above freezing with no moisture, there isn’t the combination of liquid water and cold surfaces needed to form engine ice, so the risk is much lower.

Engine ice forms when moisture is present in the air at or near freezing and the engine surfaces are cold enough to freeze that moisture on contact. In flight, visible moisture such as clouds, fog with liquid water, rain, drizzle, or snow, especially near or below freezing, provides liquid droplets that can strike the engine and freeze quickly on impact. Supercooled droplets remain liquid down to subfreezing temperatures and then freeze upon hitting the hot engine surfaces, creating ice buildup on inlets and surrounding areas.

If the air is dry, or if temperatures are well above freezing with no moisture, there isn’t the combination of liquid water and cold surfaces needed to form engine ice, so the risk is much lower.