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A pilot of a small single-engine piston aircraft is en-route in icing conditions. The pilot has been periodically checking the wings for ice accretion initially; he/she notices some slight translucent ice and the formation of white horns, followed shortly after that by the ice changing to an opaque (white) colour with a uniform thickness and some remaining horn formation. What are these observations typical characteristics of?
  • A
    Clear ice.
  • B

    Freezing rain.

  • C

    Mixed ice.

  • D

    Rime ice.

Refer to figure.
The observations described are typical characteristics of mixed ice, which is a combination of both clear ice and rime ice.

Initially there is formation of clear ice which forms when supercooled drops or droplets come into contact with a surface and freeze slowly. This type of ice accretion is denser, harder, and more transparent than rime ice. It alters the aerodynamics of the aircraft's wings and poses a significant hazard to flight. Clear ice starts as dense translucent ice with the formation of white horns.

Rime ice is a white opaque deposit with a light texture. It is caused by small, supercooled water droplets that freeze quickly. There is little or no flowback due to the speed of freezing, and therefore, the ice grows out from the leading edges and is compacted by the airstream.

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