Definition
Deposits of ice that form and build up on the external surfaces of an aircraft — wings, control surfaces, propellers, antennas, windshields, and inlets — when supercooled water droplets or moist air contact the airframe at or below freezing temperatures. The accumulation alters the shape of aerodynamic surfaces, adds weight, increases drag, reduces lift, and can disrupt the operation of control surfaces, engines, and instruments.
Plain English
Ice that builds up on the outside of the aircraft during flight. As it grows, it changes the shape of the wings and other surfaces, makes the airplane heavier, and makes it harder to fly.
Context Anchor
Seen in icing weather, preflight inspections, weather briefings, and discussions of aircraft performance in cold or wet conditions.
Derivation
Accretion comes from the Latin accrescere, meaning 'to grow onto' or 'to add to.' It describes something that builds up gradually by layer, which is exactly how flight ice forms — droplet by droplet, freezing on contact with the airframe.
Why Pilots Care
Ice changes wing shape, reduces lift, increases drag and weight, and can block control surfaces or engine inlets, leading to loss of performance or control.
Analogy
It is like trying to fly with the airplane’s smooth surfaces covered in rough, uneven crust. The shape the air was designed to flow over has been changed.
Grounding Statement
Picture a smooth wing becoming rough and lumpy as wet, cold air freezes onto it during flight.
Intuition Check
Do not assume ice accretions are only a thick, obvious coating. A thin or rough layer of ice on the airframe can still seriously affect how the airplane handles.
Example Sentence 1
The pilot exited the cloud layer as soon as ice accretions on the airframe began to form along the wing leading edges.
Example Sentence 2
The pilot activated the wing boots to shed ice accretions on the airframe before the buildup could alter the airfoil shape.