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These definitions are not intended to be official scientific explanations,
but merely to serve as operational definitions suitable to the aviation community
for the purpose of this training. These terms should not be used interchangeably.
Flat Light
Flat light is an optical illusion, also known as "sector or partial white out."
It is not as severe as "white out" but the condition causes pilots to lose
their depth-of-field and contrast in vision. Flat light conditions are usually
accompanied by overcast skies inhibiting any good visual clues. Such conditions can
occur anywhere in the world, primarily in snow covered areas but can occur in dust,
sand, mud flats, or on glassy water. Flat light can completely obscure features of
the terrain, creating an inability to distinguish distances and closure rates.
As a result of this reflected light, it can give pilots the illusion of ascending or
descending when actually flying level. However, with good judgment and proper
training and planning, it is possible to safely operate an aircraft in flat light
conditions.
White Out
As defined in meteorological terms, white out is when a person becomes engulfed
in a uniformly white glow. The glow is a result of being surrounded by blowing
snow, dust, sand, mud or water. There are no shadows, no horizon or clouds and
all depth-of-field and orientation are lost. A white out situation is severe in
that there aren't any visual references. Flying is not recommended in any
white out situation. Flat light conditions can lead to a white out environment
quite rapidly, and both atmospheric conditions are insidious: they sneak up on you
as your visual references slowly begin to disappear. White out has been the cause
of several aviation accidents in snow-covered areas.
Self Induced White Out
This effect typically occurs when a helicopter takes off or lands on a snow-covered
area. The rotor down wash picks up particles and re-circulates them through the
rotor system. The effect can vary in intensity depending upon the amount of light
on the surface. This phenomenon can happen on the sunniest, brightest day with good
contrast everywhere. However, when it happens, there can be a complete loss of
visual clues. If the pilot has not prepared for this immediate loss of visibility,
the results can be disastrous.
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