BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

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AFMAN 11-217V1 3 JANUARY 2005
17.3.2.1. Blending of Earth and Sky. At night with both aided and unaided vision,
pilots may confuse ground lights with stars. In doing so, the possibility exists of
flying into the ground because the perceived horizon is below the actual horizon.
Pilots may also confuse unlighted areas of the earth with an overcast night sky. If
pilots erroneously perceive ground features (such as the seashore) as the horizon, they
are in danger of flying into the unlighted water or terrain above it. A pilot flying with
aided night vision may see a fairly bright light source and mistake it for an aircraft or
ground light, when in fact it is a distant star with high near infrared energy that is
barely visible with unaided vision.
17.3.2.2. NVG Flight Over Water. Flight over water is particularly dangerous with
NVGs due to the significantly reduced contrast, absence of features, and lack of
motion cues in the NVG image. Also, a frequent cause of spatial disorientation with
NVGs has been the reflection of stars by water surfaces. Hazy conditions over water
can cause disorientation and force almost total reliance on flight instruments.
Therefore, NVG flight over water must be conducted with an increased reliance on
instruments as if the aircraft were in IMC. Because of the number of illusions that
can occur, extraordinary vigilance must be maintained in the aircrew’s crosscheck
between outside visual references and instrument references to prevent
misinterpretation of the NVG scene.
17.3.2.3. False Vertical and Horizontal Cues. Flying over sloping cloud decks or
land that slopes gradually upward into mountainous terrain often compels pilots to fly
with their wings parallel to the slope, rather than wings-level, or to climb or descend
with the slope. A related phenomenon is the disorientation caused by the aurora
borealis in which false vertical and horizontal cues generated by the aurora result in
attitude confusion in pilots trying to fly formation or refuel at night in northern
regions. This illusion has been called the visual form of the Leans. The other form of
the Leans is primarily the result of semicircular canal stimulation.
17.3.2.4. No Vertical or Horizontal Cues. This situation is especially hazardous
during night formation flights when the only outside reference is the lights of the lead
aircraft. Frequent cockpit instrument scans, to include altitude, are essential when
taking “spacing.” Keeping the leader’s lights in the same relative position on the
windscreen does not ensure adequate horizontal or vertical spacing, nor does it ensure
adequate height above the terrain. Especially during deceleration, when aircraft pitch
attitude increases, keeping lead in the same position on the windscreen can cause a
substantial loss of altitude. Night intercepts are especially dangerous without
frequent instrument crosschecks. An overshoot and subsequent pullback toward lead
can be confusing if you think that you are below the lights when in reality you are
level (altitude-wise) with the lights but in a 90-degree bank. A maneuver to offset
yourself to one side or the other, or below, could have disastrous results. When
displacement is behind and below the lead aircraft, the misperception of actual
altitude has been termed the DIP Illusion.
17.3.2.5. Undetected IMC. A particularly hazardous regime exists when flying with
NVGs in weather conditions conducive to the formation of thin clouds or fog. NVGs
are primarily sensitive to near infrared energy, and near infrared energy is poorly
reflected by moisture. Aircrew using NVGs will be able to detect dense clouds or