Icing

Question 1

Threat of icing

Answer 1

Reduced aerodynamic performance
Restricted ac controls
Reduced visibility
Increased stall speed
Instrument error

Question 2

Conditions for airframe icing

Answer 2

Visible moisture —————- > super cooled water droplets
Temps below 0 degrees C— > super cooled water droplets
aircraft to stick to

2 sizes of super cooled water droplets
- small droplets — > exist down to - 40 degrees

• large droplets — > -15/ -20
  Only supported by Cu/Cb clouds

Question 3

Types of airframe icing

Answer 3

Hoar frost
Rime ice
Clear ice
Rain ice
Mixed ice

Question 4

Hoar frost

Answer 4

From clear skies and light winds (high pressure systems) - frost forms either

Early mornings in winter
Descending through a warm layer in the atmosphere due to an emergency
From bottom of the atmosphere climbing through an inversion

Can depart with a cold soaked wing

Question 5

Rime ice

Answer 5

Typically stratiform cloud
Temp 0 degrees C - -40 degrees C
Small droplets freeze instantly after contact with leading edge and ice grows forwards trapping air = white
Weak and brittle

Question 6

How to remove rime ice

Answer 6

Boot
Wet wing
Heating mat

Question 7

Clear ice

Answer 7

Temp between 0 - -20 degrees C
Large droplets freeze and roll backwards from the leading edge (flow back/rollback)
Success droplets build on the flow back and laminates itself
Heavy, clear glassy appearance because the air escapes
DIFFICULT TO REMOVE

Cb, TCu, dense Ns

Question 8

Mixed ice

Answer 8

Combination of clear and rime ice
2 horn shapes form on your leading edge
Nimbostratus, Cu, Cb

Question 9

Freezing rain

Answer 9

See diagrams

Question 10

Factors affecting icing severity

Answer 10

• size of droplet
• amount of droplets - determined by stability, bottom of cloud base temp
• wing shape
  Thin wings - drops hit leading edge more often than thick wings hence a greater risk
  -Orographic intensification
• faster = more ice

Question 11

Intake icing

Answer 11

Can accumulate around intakes leading to power loss + reduction
Ice build up on defang blades = degrade aerodynamic performance
Risk of ice being ingested leading to structural damage

Question 12

Ice crystal icing

Answer 12

NOT SUPERCOOLED DROPLETS
crystals
Go into engine and cool fan blades
Fan blades cannot melt all the crystals due to fan blades being cooled down - causes stickiness = engine shut down