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Which of the following combinations of symptoms is correct regarding the whiteout phenomenon?
  • A
    Severely reduced visibility, disorientation, reference points in shadow.
  • B
    Severely reduced visibility, disorientation, opaque horizon.
  • C
    Severely reduced visibility, loss of horizon and reference points, disorientation.
  • D

    Reduced visibility, opaque reference points, disorientation.

Refer to figures.
One classic illusion for pilots is whiteout, defined by the American Meteorological Society as:

  • An atmospheric optical phenomenon of the polar regions in which the observer appears to be engulfed in a uniformly white glow.

Whiteout typically occurs over unbroken snow cover beneath a uniformly overcast sky, when the light from both is about the same. Blowing snow doesn't help, and it's particularly a problem if the ground is rising. In fact, there are several versions of whiteout:

  • Overcast Whiteout, which comes from complete cloud cover with light being reflected between a snow surface and the cloud base. Perspective is limited to within a few feet, but the horizontal visibility of dark objects is not materially reduced.

  • Water Fog. Thin clouds of supercooled water droplets contacting a cold snow surface. Horizontal and vertical visibility is affected by the size and distribution of the water droplets.

  • Blowing Snow. Winds over 20 kts picking up fine snow from the surface, diffusing sunlight and reducing visibility down to 1 m.

  • Precipitation. Small wind-driven snow crystals from low clouds with the Sun above. Light is refracted and objects obscured caused by multiple reflection of light between the snow covered surface and the cloud base. Spectral reflection from the snow flakes and obscuration of landmarks by the falling snow are further complications.

Once you suspect it, immediately climb or level off towards an area where you can see things properly. Do not be tempted to go on instruments. Better yet, put the machine on the ground before you get anywhere near whiteout conditions.

Whiteout will make distances and altitudes harder to estimate. The pilot can see only dark nearby objects - no shadows, horizon or clouds, and loses depth perception. In other words, it is difficult to distinguish between the ground and the sky. (The naked eye cannot detect the snow-covered surface because of the lack of normal colour contrast).

Therefore the correct answer is "Severely reduced visibility, loss of horizon and reference points, disorientation".

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