AIM

4/3/14

7−5−11

Potential Flight Hazards

7

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5

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13. Flying in Flat Light 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. 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

runway.

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.)