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PPL » Meteorology » Aircraft Icing

8.28 Aircraft Icing

8.28.2 List the hazards of airframe icing to aircraft in flight.

  • Increased drag
  • Increased all up weight
  • Distortion of aerodynamic shape
  • Increased Vs (increased weight, decreased lift)
  • Loss of thrust
  • Loss of aerials, CofG, pitot/static blockage and visibility.
  • Reduced lift


8.28.4 Explain the processes involved in the formation of hoar frost on an aircraft on the ground and in flight.

When the airframe temperature is below freezing and the environment air is moist but not necessarily saturated.

Deposition can occur causing water vapour to change directly to ice.

Hoar frost may form on the ground while taxing or when aircraft flying at altitude descends into warmer moist air.

The water vapour in contact with the cold aircraft sticks instantly to the airframe.

As mentioned earlier, this process is called deposition and occurs when the water vapour changes directly to its solid state bypassing the liquid state.


8.28.6 State the dangers of hoar frost and the actions required to alleviate these dangers on the ground and in flight.

Hoar frost is a type of ice crystal that forms on surfaces when the air temperature drops below freezing and there is moisture in the air.

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