Icing

Question 1

What causes icing on an aircraft?

Answer 1

Contact with supercooled water droplets

Question 2

What are the 4 different types of aircraft icing?

Answer 2

Clear ice
Rime ice
Rain ice
Hoar frost

Question 3

What causes Hoar frost?

Answer 3

Hoar frost happens outside of a cloud base.

It is due to direct sublimation onto the aerofoil (Water vapour —> Ice)

Question 4

Give details about Clear ice

Answer 4

Large supercooled water droplets - allowing for throwback
Occurs between 0 & -20°C

It is dense, and difficult to dislodge

Occurs within TCU and CB’s

Question 5

Give details about Rime ice

Answer 5

Small supercooled water droplets
Occurs between 0 & -40°C

Freezes rapidly, resulting it little throwback
Traps air - making it opaque, white and brittle

Occurs in NS, SC, AS + ST

Question 6

Give details about Rain ice

Answer 6

Supercooled water droplets
Occurs where rain fails above 0°C, but falls through an area below 0°C
Rain ice can build up very rapidly

Associated with warm fronts + occlusion
Occurs below NS

Question 7

Give details about Hoar frost

Answer 7

Occurs outside of any cloud base by sublimation (vapour - ice)
Can form both on the ground, or whilst airborne

Accumulation is normally slow

Question 8

Why should Hoar frost not be ignored before take off?

Answer 8

Hoar frost can cause a very early + abrupt peak on the lift curve - followed by a sharp drop in lift, as separation occurs

This can lead to early stall during T/O and flight

Therefore, ensure any hoar frost is detected, and anti-ice applied quickly after de-icing

Question 9

What are the 4 different intensities of aircraft icing?

Answer 9

Trace: Not hazardous, unless builds for 1+ hour

Light: May pose a problem if builds for 1+ hour

Moderate: Short encounters my pose a problem. Divert/de-ice

Severe: De-icing equip. fails to control the hazard. Divert immediately

Question 10

What are the three aircraft icing intensity symbols?

Answer 10

(In order)
A large U:
With 1, 2, or 3 lines vertically through the base

Question 11

Does speed affect ice accretion?

Answer 11

Yes, the greater the airspeed - the greater the risk of ice accretion

Due to more flow back and interception

Question 12

State increase/no effect/decrease effect of ice on the following factors:
Lift, Weight, Thrust, Drag

Answer 12

Lift - Decreases

Weight - Increases

Thrust - Decreases

Drag - Increases