Written with AI assistance and may contain mistakes. Verify against the official Transport Canada publications before relying on anything here.

Structural icing: conditions, supercooled water & ice types

Structural icing = ice building on airframe in flight. Needs both at once (TC AIM AIR 2.12.3.1):

Water is supercooled: liquid below 0 °C until it touches aircraft and freezes.

Supercooled water (AWH 20.2):

Does not freeze on its own until about −40 °C
Droplet surface tension resists freezing: smaller and purer droplet = more supercooled

Cloud water by temperature (AWH 20.2):

Temperature	Cloud water
0 °C to −10 °C	Mostly liquid supercooled droplets
−10 °C to −20 °C	Mix of droplets and ice crystals
Below −20 °C	Almost entirely ice crystals; strong updraft can carry supercooled water down to −40 °C

Ice types: drop size decides (TC AIM MET Table 2.4). Temperature and liquid water content also matter (TC AIM AIR 2.12.3.1).

	Clear (glaze) ice	Rime ice
Drops	large, supercooled	small, supercooled
Freezing	slow, spreads back	instant, on contact (traps air)
Looks	hard, clear, glossy, smooth, heavy	opaque, milky white, rough, brittle, light
Found in	freezing rain	light drizzle
Hazard	worst: hard to remove, heaviest	lighter, easier to shed
Temp	favours warmer than −10 °C	favours colder than −15 °C (mixed ice in between, AWH 20.3.4)
Liquid water content	higher	lower

Mixed ice: both at once, from cloud holding a range of drop sizes.
Cloud type sets liquid water: cumuliform most, stratiform least (AWH 20.3.4).
Big drop: much unfrozen water runs back before setting, glazes a clear sheet.
Small drop: freezes on landing, traps air between grains, white and crumbly.

Trap: cold air alone or cloud alone forms no structural ice; clear vs rime is set by drop size, not temperature alone.

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