Definition
A type of structural ice that forms as a smooth, glossy, transparent or translucent sheet on aircraft surfaces when large supercooled water droplets strike the airframe and freeze relatively slowly. Because the droplets spread out before freezing, clear ice bonds tightly to the surface and is hard to see and hard to remove.
Plain English
A kind of ice that builds up on the airplane as a smooth, glassy layer. It looks like a thin coat of polished glass and sticks firmly to whatever it forms on.
Context Anchor
Seen in aircraft icing discussions, especially when comparing clear ice with rougher, whiter ice types.
Derivation
The word 'clear' is used here in its visual sense — see-through. The ice is called 'clear' because you can see through it, unlike rime ice, which is white and opaque. Knowing this helps pilots remember that clear ice is dangerous partly because it's hard to spot during a visual check.
Why Pilots Care
Clear ice is the most dangerous form of structural icing. It is heavy, sticks tightly to the airframe, distorts the shape of the wing and control surfaces, and is difficult to see during a walk-around or in flight. It can build up quickly and is harder for de-icing systems to shed than rime ice.
Analogy
Clear ice is more like a hard glaze of ice on a windshield than a powdery layer of frost.
Intuition Check
Clear does not mean safe, harmless, or free of ice here. In this context, clear means a transparent or glassy type of aircraft ice.
Example Sentence 1
After descending through the freezing layer, the pilot noticed clear ice forming along the leading edge of the wing.
Example Sentence 2
Clear ice is difficult to detect visually because it follows the shape of the airfoil closely.