Private Pilot Private Practice Exam

Structural icing typically occurs when an aircraft flies through an environment where there is visible moisture present, such as clouds, rain, or fog, combined with conditions that allow for the freezing of that moisture. When flying in these conditions, supercooled water droplets can exist, which do not freeze immediately upon contact with surfaces of the aircraft. This moisture can freeze on impact, leading to icing on wings, control surfaces, and other critical parts of the aircraft.

For icing to develop, the presence of visible moisture is essential, as it is the source of the water that can freeze and adhere to the aircraft's surfaces. Therefore, the critical factor for the occurrence of structural icing during flight is the presence of visible moisture.

While other conditions such as cool temperatures and altitude can contribute to or influence the likelihood of icing, they alone do not establish the necessary conditions for structural icing to occur. Cool temperatures facilitate the freezing process once moisture is present, but without visible moisture, icing cannot form.