Icing Flashcards
5 threats associated with icing
- Reduced aerodynamic performance
- Restricted aircraft controls
- Reduced visibility
- Increased stall speed
- Instrument error/blocked instruments
Why does icing happen?
Water can remained supercooled below 0 degrees down to -40 degrees, if a disturbance occurs (an aircraft) the after droplets will freeze on impact
How is clear ice formed?
Large supercooled water droplets hit the aircraft and then as they flow back over the surface they freeze, typical between 0 and -15 degrees
What 2 factors increase the risk of icing?
- Greater risk at higher speed
2. Greater risk with a thin wing rather than a thicker, deeper one
What are the 5 main types of ice?
- Clear ice
- Rime ice
- Mixed ice
- Hoar frost
- Freezing rain
What clouds is clear ice found in?
Cb, Cu and dense Ns
How is rime ice formed?
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
What clouds is rime ice found in?
As, Ac, St, Sc and Ns
Where do you find mixed ice?
Transition between clear and rime
- 20 degrees for Cu/Cb
- 10 degrees for Ns
- 20 degrees for Ns with orographic lifting
What is hoar frost?
Formed on clear, calm days through sublimation. Water vapour comes into contact with very cold surface, such as cold fuel tanks, and freezes instantly
Where would you find freezing rain?
Where a warm front meets a cold front in the rain ice triangle
What are the dangers of snow?
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
What is engine icing?
When ice builds up around the intakes and on the fan blades of an engine
What is high altitude ice crystal icing?
Large quantities of ice crystals can be present at high altitudes
Primarily found at the top of Cb’s, squall lines and tropical storms
What are the dangers of ice crystal icing?
Primarily effect engines, large amount can accumulate and cause damage. Melting also cools the engines core and can result in a reduction of power
How does icing effect a piston engine?
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
What is the risk of icing in high cloud (Ci, Cs, Cc)?
Very low risk, very cold but very little water content
What is the risk of icing in mid level clouds (As, Ac)?
Light to moderate, depends on the freezing level, clear ice possible up to 5000ft above the freezing level, above that rime ice
What is the risk of icing in low level clouds (St, Sc, Cu)?
Light to moderate risk, depends on the water content, normally experience clear ice however rime ice is possible if cold enough
What is the risk of icing in low level clouds (Cb, Ns)?
Moderate to severe, cloud can contain high water content, mostly clear ice but rime ice at higher levels
What is the orographic effect?
The air being forced up by an obstacle, sun as a mountain, can increase the severity of icing in a cloud
