Structural Icing Explained
Why ice forms on an airframe, the types of icing, and how it degrades performance.
Structural icing forms when an aircraft flies through visible moisture (cloud or rain) at a temperature at or below freezing. Supercooled water droplets — still liquid below 0 °C — freeze on impact with the airframe.
Types of ice
- Rime ice — milky and brittle, from small droplets freezing fast; roughens the surface.
- Clear ice — glossy and hard, from large droplets freezing slowly; heavy, hard to shed and dangerous.
- Mixed ice — a combination, the most common in practice.
Why it's dangerous
Ice changes the shape of the wing, which:
- Reduces lift and raises the stall speed — a wing can stall at a much higher airspeed than normal.
- Increases drag and weight, degrading climb and range.
- Can jam controls, block the pitot/static system, and ice the propeller and antennas.
Avoidance
Most light aircraft are not certified for flight into known icing (FIKI). The plan is avoidance: know the freezing level, avoid visible moisture near and below it, and have an escape — a climb to colder/drier air, a descent to above-freezing air, or a 180° turn. Supercooled large droplet (SLD) conditions and freezing rain are especially hazardous and demand an immediate exit.
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*Reference and training only — not for navigation. Always consult the current AIM, FAR/AIM, your aircraft’s POH/AFM, official weather products and a certificated flight instructor.*