AIM
3/21/24
4.
Blowing sand and dust can cause an illusion of a tilted horizon. A pilot not using the flight instruments
for reference may instinctively try to level the aircraft with respect to the false horizon, resulting in an accident.
Helicopter rotor wash also causes sand to blow around outside the cockpit windows, possibly leading the pilot
to experience an illusion where the helicopter appears to be turning when it is actually in a level hover. This can
also cause the pilot to make incorrect control inputs which can quickly lead to disaster when hovering near the
ground. In night landings, aircraft lighting can enhance the visual illusions by illuminating the brownout cloud.
c. White Out.
As defined in meteorological terms, white out occurs 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
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of
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field and orientation are lost. A white out situation is
severe in that there are no 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.
d. Self Induced White Out.
This effect typically occurs when a helicopter takes off or lands on a
snow
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covered area. The rotor down wash picks up particles and re
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circulates them through the rotor down wash.
The effect can vary in intensity depending upon the amount of light on the surface. This 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.
Good planning does not prevent one from encountering flat light or white out conditions.
e. Never take off in a white out situation.
1.
Realize that in flat light conditions it may be possible to depart but not to return to that site. During takeoff,
make sure you have a reference point. Do not lose sight of it until you have a departure reference point in view.
Be prepared to return to the takeoff reference if the departure reference does not come into view.
2.
Flat light is common to snow skiers. One way to compensate for the lack of visual contrast and
depth
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of
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field loss is by wearing amber tinted lenses (also known as blue blockers). Special note of caution:
Eyewear is not ideal for every pilot. Take into consideration personal factors—age, light sensitivity, and ambient
lighting conditions.
3.
So what should a pilot do when all visual references are lost?
(a)
Trust the cockpit instruments.
(b)
Execute a 180 degree turnaround and start looking for outside references.
(c)
Above all
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fly the aircraft.
f. Landing in Low Light Conditions.
When landing in a low light condition
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use extreme caution. Look
for intermediate reference points, in addition to checkpoints along each leg of the route for course confirmation
and timing. The lower the ambient light becomes, the more reference points a pilot should use.
g. Airport Landings.
1.
Look for features around the airport or approach path that can be used in determining depth perception.
Buildings, towers, vehicles or other aircraft serve well for this measurement. Use something that will provide
you with a sense of height above the ground, in addition to orienting you to the runway.
2.
Be cautious of snowdrifts and snow banks
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anything that can distinguish the edge of the runway. Look
for subtle changes in snow texture or shading to identify ridges or changes in snow depth.
h. Off
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Airport Landings.
1.
In the event of an off
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airport landing, pilots have used a number of different visual cues to gain reference.
Use whatever you must to create the contrast you need. Natural references seem to work best (trees, rocks, snow
ribs, etc.)
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Potential Flight Hazards