Icing

Question 1

Range of temperatures/sizes that SCWD exist

Answer 1

0 to -15C : Large SCWD
-15 to -40C : Small SCWD
Colder than -40C : Most droplets frozen

Question 2

Hoar Frost

Answer 2

Caused by water vapour sublimating straight into ice.
Requires moist air and cold airframe.
Can occur : Overnight, descending from altitude, flying from cold air into warm front

Question 3

What are SCWD

Answer 3

Water droplets with a temperature below 0C, that haven’t frozen as there is no condensation nuclei for them to freeze to

Question 4

Rime Ice

Answer 4

Small SCWD (-15 to -40) hit airframe that is below freezing and freeze on contact.
Air bubbles trapped, opaque and white appearance.
Builds up from leading edge.

Question 5

Clear Ice

Answer 5

Large SCWD hit airframe below 0C.
As droplets are larger they take longer to freeze so latent heat released during freezing allows ice to move further down wing.
Heavier than rime ice.
Forms thick sheet of ice which is tough to remove using de-icing equipment.

Greatest risk in medium level cumuliform and Ns with orographic intensification.

Question 6

Mixed Ice

Answer 6

Combination of Rime and Clear Ice
Flow back, build up from leading edge
Severe build up = Double horn

Question 7

Risk of icing in cumuliform cloud…

Answer 7

Severe between 0 and -20C
Reduced between -20 & -40C
Unlikely below -40C

Question 8

Risk of icing in Stratiform cloud…

Answer 8

0 & -10C = Moderate severity

Colder than -10C = Light severity

Question 9

As/Ns/Ac cloud icing

Answer 9

0 to -15C = Moderate to Severe
With orographic uplift = moderate to severe down to -20C.

Ac has greater vertical extent = SCWD down to -30C.