Definition
The buildup of ice on the surfaces of an aircraft when it flies through visible moisture (such as cloud, freezing rain, or freezing drizzle) at temperatures at or below freezing. Ice accumulation can form on wings, tail surfaces, propellers, antennas, windshields, engine inlets, and pitot-static probes, and its rate and shape depend on droplet size, temperature, airspeed, and time spent in icing conditions.
Plain English
Ice building up on the outside of the airplane while flying through cold, wet air.
Context Anchor
Seen in instrument flying and structural icing discussions, especially when flying in clouds, precipitation, or near-freezing temperatures.
Derivation
From Latin accumulare, meaning 'to heap up' or 'to pile on.' The word emphasizes that ice doesn't just appear — it grows progressively as the aircraft continues to fly through icing conditions.
Why Pilots Care
Reduces lift, increases drag and weight, and can lead to loss of control or forced diversion if allowed to continue.
Grounding Statement
Picture frost slowly thickening on a freezer shelf — except it's happening on the leading edge of a wing at 150 knots, and the longer you stay there, the more it grows.
Intuition Check
Do not assume ice accumulation means a thick, obvious layer of ice. In aviation, even a thin or rough coating can be significant because it changes how air flows over the aircraft.
Example Sentence 1
After ten minutes in the clouds near freezing level, the pilot noticed ice accumulation on the wing's leading edge and requested a lower altitude.
Example Sentence 2
Even light ice accumulation on the propeller reduced engine efficiency and required immediate action.