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When flying through visible moisture, how can the TAT indication be useful?
  • A
    To calculate TAS from CAS.
  • B
    To determine outside air temperature.
  • C
    To determine if there is icing.
  • D
    To correct for density altitude.

The airframe may become contaminated by ice, frost or water either whilst it is in flight or when standing on the ground.

The formation of ice and frost on the airframe will:
- modify the profile of the aerofoil.
- increase the roughness of the aircraft surface.
- increase the weight of the aircraft.

Tests have shown that frost, ice or snow with the thickness and surface roughness of medium or coarse sandpaper reduces lift by as much as 30% and increases drag by 40%.

‐ Icing conditions exist when the OAT (on ground or after takeoff) or the TAT (in flight) is at or below 10 °C and visible moisture in any form is present (such as clouds, fog with visibility of 1 sm (1 600 m) or less, rain, snow, sleet or ice crystals).
‐ Icing conditions also exist when the OAT on the ground and for takeoff is at or below 10 °C and operating on ramps, taxiways or runways where surface snow, standing water or slush may be ingested by the engines, or freeze on engines, nacelles or engine sensor probes.

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