Which type of icing is considered most dangerous for aircraft?

Clear icing is considered the most dangerous type of icing for aircraft primarily because it forms a transparent layer of ice that adheres tightly to the surfaces of an aircraft. This type of icing usually occurs when supercooled liquid droplets collide with the aircraft and freeze on impact, creating a smooth, dense layer of ice.

The danger of clear icing lies in the fact that it can significantly affect the aerodynamic properties of the aircraft by increasing weight, altering airflow, and reducing lift. As the ice accumulates, it makes the aircraft less maneuverable and can lead to control issues. In contrast to rime icing, which has a more irregular structure and can be easier to detect, clear icing is less visible and can create serious safety hazards before pilots are even aware that icing has occurred.

Mixed icing, while also dangerous, generally combines characteristics of both clear and rime icing, which may not be as severe as clear icing alone. Structural icing, though a term that can apply broadly, is not a specific category recognized in the same way by aviation safety standards. Therefore, the fact that clear icing can form a hazardous layer that is challenging to detect and manage makes it the most perilous type of icing for aircraft operations.