Definition
A glossy, transparent or translucent layer of ice that forms on aircraft surfaces when relatively large supercooled water droplets strike the airframe and freeze slowly, allowing the water to spread out before solidifying. Clear ice is dense, hard, heavy, and tightly bonded to the surface, making it the most dangerous form of structural icing.
Plain English
A smooth, see-through coat of ice that builds up on the aircraft when large cold water drops hit it and slowly freeze across the surface. It is heavy, sticks firmly, and is hard to remove.
Context Anchor
Seen in icing weather discussions, pilot reports, and in flight when an aircraft is in visible moisture near or below freezing temperatures.
Derivation
Called "clear" because the ice forms with very few air bubbles trapped inside, so it looks glassy and transparent rather than white. The slow freezing of large droplets lets the water settle and exclude air before it hardens.
Why Pilots Care
Clear icing is difficult to detect visually and can form heavy, irregular shapes that severely reduce lift and increase drag.
Analogy
It is like a smooth glaze of ice on a windshield: it may look shiny and clean, but it is still a solid layer that changes the surface underneath.
Grounding Statement
Picture rain hitting a freezing windshield and spreading into a glassy sheet before it solidifies -- that same process happening on a wing in flight is clear icing.
Intuition Check
Do not read clear as safe or absent. In clear icing, clear means smooth and glassy-looking ice, not a clear airplane.
Example Sentence 1
After descending through a layer of freezing rain, the pilot noticed clear icing forming along the leading edge of the wing and immediately requested a climb to warmer air.
Example Sentence 2
Clear icing adhered tightly to the wings and was harder to remove than rime ice with the available de-icing boots.