Definition
A rough, opaque, milky-white deposit of ice that forms on aircraft surfaces when small, supercooled water droplets freeze almost instantly on contact, trapping air between the frozen droplets. It typically forms in stratiform clouds at colder temperatures and accumulates on leading edges, probes, and antennas.
Plain English
A bumpy, frosty-looking layer of ice that builds up on the aircraft when tiny cold water drops hit it and freeze straight away, trapping air bubbles that make it look white and rough.
Context Anchor
Seen in aircraft icing discussions, preflight inspections, deicing work, and reports of ice on wings, propellers, struts, antennas, or other exposed surfaces.
Derivation
‘Rime’ is an Old English word for hoarfrost or frozen mist. Knowing it simply means ‘frost’ helps fix the picture: a frosty, white coating rather than a smooth, glassy one.
Why Pilots Care
The rough buildup disrupts smooth airflow, reducing lift and increasing drag, which can make the aircraft harder to control.
Analogy
Rime ice is like the rough white frost that can form on a freezer wall: it is not smooth, clear ice, and its uneven surface is part of the problem.
Grounding Statement
Picture flying through cold cloud droplets that hit the airplane and freeze so fast that the ice turns white and rough instead of clear and smooth.
Intuition Check
Do not confuse rime ice with clear ice or ordinary frost on the ground. Rime ice forms on the aircraft when cold liquid droplets strike it in flight or in freezing moisture and freeze rapidly.
Example Sentence 1
After climbing through a layer of stratus at minus ten degrees, the crew noticed a rough white coating of rime ice along the wing’s leading edge.
Example Sentence 2
Pre-flight checks included looking for any rime ice that might have accumulated overnight on the parked aircraft.