Icing

Question 1

5 threats associated with icing

Answer 1

1. Reduced aerodynamic performance
2. Restricted aircraft controls
3. Reduced visibility
4. Increased stall speed
5. Instrument error/blocked instruments

Question 2

Why does icing happen?

Answer 2

Water can remained supercooled below 0 degrees down to -40 degrees, if a disturbance occurs (an aircraft) the after droplets will freeze on impact

Question 3

How is clear ice formed?

Answer 3

Large supercooled water droplets hit the aircraft and then as they flow back over the surface they freeze, typical between 0 and -15 degrees

Question 4

What 2 factors increase the risk of icing?

Answer 4

1. Greater risk at higher speed

2. Greater risk with a thin wing rather than a thicker, deeper one

Question 5

What are the 5 main types of ice?

Answer 5

1. Clear ice
2. Rime ice
3. Mixed ice
4. Hoar frost
5. Freezing rain

Question 6

What clouds is clear ice found in?

Answer 6

Cb, Cu and dense Ns

Question 7

How is rime ice formed?

Answer 7

When it is colder than -15 degrees and the ropes are smaller. Water freezes instantly trapping air giving it its white colour. No flow back due to instantaneous freeze

Question 8

What clouds is rime ice found in?

Answer 8

As, Ac, St, Sc and Ns

Question 9

Where do you find mixed ice?

Answer 9

Transition between clear and rime

• 20 degrees for Cu/Cb
• 10 degrees for Ns
• 20 degrees for Ns with orographic lifting

Question 10

What is hoar frost?

Answer 10

Formed on clear, calm days through sublimation. Water vapour comes into contact with very cold surface, such as cold fuel tanks, and freezes instantly

Question 11

Where would you find freezing rain?

Answer 11

Where a warm front meets a cold front in the rain ice triangle

Question 12

What are the dangers of snow?

Answer 12

Not generally a problem in flight
If it is mixed with supercooled droplets may increase the rate of ice accumulation on an aircraft
Greater hazard on the ground

Question 13

What is engine icing?

Answer 13

When ice builds up around the intakes and on the fan blades of an engine

Question 14

What is high altitude ice crystal icing?

Answer 14

Large quantities of ice crystals can be present at high altitudes
Primarily found at the top of Cb’s, squall lines and tropical storms

Question 15

What are the dangers of ice crystal icing?

Answer 15

Primarily effect engines, large amount can accumulate and cause damage. Melting also cools the engines core and can result in a reduction of power

Question 16

How does icing effect a piston engine?

Answer 16

Fuel evaporation cools the carburettor chamber which can lead to ice build up. Ice can restrict of block the flow of fuel to the engine and cause a failure if not monitored. Can occur in temperatures well above 0 degrees

Question 17

What is the risk of icing in high cloud (Ci, Cs, Cc)?

Answer 17

Very low risk, very cold but very little water content

Question 18

What is the risk of icing in mid level clouds (As, Ac)?

Answer 18

Light to moderate, depends on the freezing level, clear ice possible up to 5000ft above the freezing level, above that rime ice

Question 19

What is the risk of icing in low level clouds (St, Sc, Cu)?

Answer 19

Light to moderate risk, depends on the water content, normally experience clear ice however rime ice is possible if cold enough

Question 20

What is the risk of icing in low level clouds (Cb, Ns)?

Answer 20

Moderate to severe, cloud can contain high water content, mostly clear ice but rime ice at higher levels

Question 21

What is the orographic effect?

Answer 21

The air being forced up by an obstacle, sun as a mountain, can increase the severity of icing in a cloud