For which type of icing is visible moisture a crucial formation factor?

Visible moisture is a crucial factor for the formation of structural icing. Structural icing occurs when supercooled liquid water freezes on contact with aircraft surfaces, which is influenced directly by the presence of visible moisture, such as cloud droplets or precipitation. When an aircraft flies through clouds or precipitation where the temperature is below freezing, and there is supercooled water present, structural icing can develop rapidly as the water freezes upon contact with the aircraft's surfaces.

In contrast, while other types of icing may occur under specific conditions, they do not depend as directly on visible moisture. Clear icing, for example, forms from large droplets of supercooled water, whereas rime icing stems from smaller droplets that freeze on contact more rapidly, creating a rougher surface. Induction icing can refer to the cooling of the air due to evaporation or condensation processes, but does not depend on the presence of visible moisture in the same manner as structural icing does. Understanding these dynamics helps in effectively recognizing and mitigating the risks associated with icing in aviation contexts.