Icing Flashcards
Define supercooled water droplets
Droplets in liquid state between 0-40ºC
Forms in all clouds but cirrus
Unstable as it wants to freeze
Colder it is the smaller the SCWD
Describe the formation of clear (glaze) ice
Large SCWD strokes aircraft and starts to freeze. Release latent heat delaying freezing and the part not freezing will flow back over the surface the freeze more.
Most dangerous as builds up quickly
Describe the formation of rime (opaque) ice
Small SCWD or small cloud droplets freeze on impact
Whole droplet becomes solid at once
Air trapped between frozen droplet make it opaque and brittle
Describe the formation of mixed ice
Mixture of large and small SCWD, builds up rime ice on leading edge and clear ice behind.
Worst effects of both
Describe the formation of hoar frost
White crystal deposit similar to frost on the ground. Occurs in clear air when airframe is below 0ºC.
Water vapour in contact with air frame deposition into ice, rapid descent from very cold region to warm moist layer or climb from cold into an inversion.
Describe the formation of freezing rain
Freezing rain develops as falling snow encounters a layer of warm air deep enough for the snow to completely melt and become rain. As the rain continues to fall, it passes through a thin layer of cold air just above the surface and cools to a temperature below freezing.
Only found ahead of a warm front
What clouds form what ice?
Clear ice forms in clouds with large droplets
- Ns, Cu, Cb
Rime ice forms in clouds with small droplets
- Ns, As, Ac, SC, St
Mixed ice = mixture
Temperature ranges of icing
Clear ice - 0-20ºC
Rime -20ºC to -40ºC
Mixed ice - 10ºC to -30ºC
What are the height ranges relative to freezing level
Clear ice = freezing level to 10,000ft
Rime = 10,000ft above to 20,000ft above FL
Mixed ice = 5,000ft to 15,000ft above FL
What are enhancing factors for ice
Frontal lifting
Orographic lifting
Convection
Updraft portion of lee waves
Explain factors that influence the rate of ice accretion
Size of the droplet - bigger is more
Number of droplets - more droplets, faster it is
Speed of aircraft - as it speeds up it collects more droplets increasing ice accretion
Design of aircraft - designed poorly can lead to increase
Hazards of icing to flight
Increase drag, weight, increased stall speed
Distortion of aerodynamic shape reducing lift
Loss of thrust due to build up on propeller
Impact icing
Pitot/static blockage
Long aerials can freeze and break off or poor reception
Fuel tank vents or battery vents blocked
List the intensity classifications of icing
•Light = Minor coverage, safe to fly through for an hour without use of de-icing/anti-icing
•Moderate = substantial build up in few minutes, must use de-icing/anti-icing
•Severe = Immediate diversion required, de-icing/anti-icing ineffective
Droplet size of different icing
Clear ice = large
Rime = small
Mixed = mix
Explain methods of avoiding or mitigating airframe icing
Avoid flying in updrafts of lenticular or any cloud
Fly higher to get below -40ºC where icing doesn’t occurs as SCWD are small
Use de-icing/anti ice equipment
Stay below freezing level
Explain deposition (ATPL)
Water vapour to ice without water droplets forming, latent heat is released warming atmosphere.
Increases instability
Describe sublimation (ATPL)
Ice to water vapour
Latent heat absorbed, cools atmosphere and increases stability
Explain what happens when an aircraft Collides with SCWD (ATPL)
Aircraft is ice nuclei, will form ice on contact with leading edge, rest will flow back and cool on the airframe.
Aircraft doesn’t need to be below 0ºC for icing
Rime ice forms when temps are colder than about - 20ºC
Clear ice forms between 0 - -20ºC
Describe the freezing rain process (ATPL)
Only occurs in warm fronts where warm rain falls into air below 0ºC same as CPL.
State areas of the globe where freezing rain is most likely to be encountered
Can happen in maritime and continental climates, most common in polar climates
Identify the symbols used to indicate different types of icing (ATPL)
Light - no symbol
Moderate - 2 lines
Severe - 3 lines