Aeronautical Information Manual (AIM), page 539

Index   538 -- Page 539 -- 540

7-5-13. Flying in Flat Light and White Out

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

b. 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.

c. 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.

d. 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-of-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 - fly the aircraft.

e. Landing in Low Light Conditions. When
landing in a low light condition - 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.
f. 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
2. Be cautious of snowdrifts and snow banks -
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.

g. Off-Airport Landings.
1. In the event of an off-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.)

Potential Flight Hazards 7-5-11

Page 539 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   538 -- Page 539 -- 540