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6/17/21 

AIM 

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13.  Flying in Flat Light, Brown Out 

Conditions, and White Out Conditions 

a.  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 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 that they are ascending or descending when 
they may actually be flying level. However, with 
good judgment and proper training and planning, it is 
possible to safely operate an aircraft in flat light 
conditions. 

b.  Brown Out.

 A brownout (or 

brown

out

) is an 

in

flight visibility restriction due to dust or sand in 

the air. In a brownout, the pilot cannot see nearby 
objects which provide the outside visual references 
necessary to control the aircraft near the ground. This 
can cause spatial disorientation and loss of situational 
awareness leading to an accident. 

1. 

The following factors will affect the 

probability and severity of brownout: rotor disk 
loading, rotor configuration, soil composition, wind, 
approach speed, and approach angle. 

2. 

The brownout phenomenon causes accidents 

during helicopter landing and take

off operations in 

dust, fine dirt, sand, or arid desert terrain. Intense, 
blinding dust clouds stirred up by the helicopter rotor 
downwash during near

ground flight causes signifi-

cant flight safety risks from aircraft and ground 
obstacle collisions, and dynamic rollover due to 
sloped and uneven terrain. 

3. 

This is a dangerous phenomenon experienced 

by many helicopters when making landing approach-
es in dusty environments, whereby sand or dust 
particles become swept up in the rotor outwash and 
obscure the pilot’s vision of the terrain. This is 
particularly dangerous because the pilot needs those 
visual cues from their surroundings in order to make 
a safe landing. 

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

of

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

covered area. The rotor down wash picks up 

particles and re

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 

Potential Flight Hazards 

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