What is the primary cause of clear icing on an aircraft?

Clear icing on an aircraft primarily occurs when large water droplets in the atmosphere collide with the aircraft's surface and break apart upon impact, subsequently freezing. This phenomenon is often associated with conditions such as warm fronts or high-stability layers, where supercooled liquids exist. The large droplets do not freeze instantly upon contact; instead, they spread out and, as they freeze, they create a smooth, transparent layer of ice, which is characteristic of clear icing.

This process is critical to understanding clear icing because it highlights the importance of droplet size in icing formation. Large droplets possess more kinetic energy than smaller ones, leading to their behavior upon impact with the aircraft. In contrast, smaller droplets freeze quickly, usually resulting in a different type of icing known as rime icing, which appears opaque and rough. Understanding this mechanism aids pilots and meteorologists in predicting and managing icing conditions during flight operations.