What causes clear ice to form on an airframe during flight?

Clear ice formation occurs primarily due to the slow freezing of large supercooled water droplets when they come into contact with the aircraft's surface. Supercooled water droplets are liquid water droplets that remain in the liquid state even at temperatures below the freezing point. When these larger droplets strike the airframe, they spread out upon impact before slowly freezing, which allows the formation of a dense, transparent layer of ice.

Unlike smaller droplets that may freeze more quickly and form rime ice, large supercooled droplets provide enough volume to create the conditions necessary for clear ice. This type of ice is particularly hazardous, as it can significantly affect aircraft performance and handling characteristics. Understanding the conditions that lead to clear ice formation is crucial for pilots to maintain safety when flying in icy conditions.