Aircraft Icing Flashcards
Define ‘super-cooled water droplets’.
- Droplet in liquid state between 0 and -40 degrees Celsius
- Form in all clouds except cirrus type
- Unstable as it wants to freeze
- The colder it is the smaller the SCWD
Describe the formation process of clear ice.
- Large SCWD strikes aircraft and starts to freeze
- Will release latent heat delaying freezing
- Part not freezing will flow back over surface then freeze
- Most dangerous form of icing as builds up quickly
Describe the formation process of rime ice.
- Small SCWD or small cloud droplets freeze on impact
- While droplet becomes solid at once
- Air trapped between frozen droplet making it opaque and brittle
Describe the formation process 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 process of hoar frost.
- White crystal deposit similar to frost on the ground
- Occurs in clear air when airframe below 0 degrees
- 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 process of freezing rain.
- Warm rain/inversion falls into 0 degree Celsius air below
- Forms both clear and rime ice
- Only found ahead of a warm front
With reference to clear, rime and mixed ice, describe the associated cloud types.
- Clear ice forms in clouds with large droplets (Ns, Cu, Cb)
- Rime ice formed in layer clouds with small droplets (Ns, As, Ac, SC, St)
- Mixed ice = mixture
With reference to clear, rime and mixed ice, describe the temperature ranges.
- Clear ice = 0 to -20 degrees Celsius.
- Rime ice = -20 to -40 degrees Celsius
- Mixed ice = -10 to -30 degrees Celsius
With reference to clear, rime and mixed ice, describe the droplet size.
- Clear ice = large
- Rime ice = small
- Mixed ice = both
With reference to clear, rime and mixed ice, describe the height range relative to the freezing level.
- Clear ice = freezing level to 10,000ft above
- Rime ice = 10,000ft above to 20,000ft above FL
- Mixed ice = 5,000ft to 15,000ft above FL
With reference to clear, rime and mixed ice, describe the enhancing factors.
- Frontal lifting
- Orographic lifting
- Convection
- Up draft portion of lee waves
Explain the factors that influence the rate of ice accretion.
- Cloud water content
- Aircraft characteristics
- Kinetic heating
- Adiabatic heating
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
List the intensity classifications of icing
- Light = Minor coverage, safe to fly though 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.
Describe the effect of different intensity classifications of icing on aircraft.
- Light = Minor coverage, safe to fly though 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.
Explain methods of avoiding or mitigating airframe icing.
- Avoid flying in up draughts of lenticulars(SEV) or any cloud.
- Fly higher to get below -40 degrees Celsius where icing does not occur as SWCD are very small.
- Use de-icing or anti-icing equipment
- Stay below freezing level
Explain the process of deposition.
- Water vapour to ice without water droplets forming
- Latent heat released, warms atmosphere
- Increases instability
Explain the process of sublimation.
- Ice directly to water vapour
- Latent heat absorbed, cools atmosphere
- Increases stability
Explain what happens when an aircraft collides with ‘supercooled water droplets’.
- Aircraft is ice nuclei
- Will form ice on contact with leading edge
- The rest will flow back and cool on the airframe
- Aircraft does not need to be below 0 degrees for icing
Describe the ‘freezing rain’ formation process.
- Only occurs in warm fronts
- Warm rain falls into air below 0 degrees Celsius where icing occurs.
State the 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 light icing.
- No symbol for light icing
Identify the symbol used to indicate moderate icing.
- Semi circle, two lines.
identify the symbol used to indicate severe icing.
- Semi circle, three lines.
