Spatial
Disorientation
Visual Illusions
OK-24-1154 9/18/2024
A Black-Hole Approach Illusion can happen during a final
approach at night (no stars or moonlight) over water or
unlighted terrain to a lighted runway beyond which the horizon
is not visible. In the example shown in (Figure 8), when
peripheral visual cues are not available to help you orient
yourself relative to the earth, you may have the illusion of
being upright and may perceive the runway to be tilted left and
upsloping. However, with the horizon visible (Figure 9) you can
easily orient yourself correctly using your central vision.
A particularly hazardous black-hole illusion involves
approaching a runway under conditions with no lights before
the runway and with city lights or rising terrain beyond the
runway. Those conditions may produce the visual illusion of a
high-altitude final approach. If you believe this illusion you may
respond by lowering your approach slope (Figure 10).
The Autokinetic Illusion gives you the impression that a
stationary object is moving in front of the airplane’s path; it is
caused by staring at a fixed single point of light (ground light or
a star) in a totally dark and featureless background. This illusion
can cause a misperception that such a light is on a collision
course with your aircraft (Figure 11).
False Visual Reference Illusions may cause you to orient your
aircraft in relation to a false horizon; these illusions are caused
by flying over a banked cloud, night flying over featureless
terrain with ground lights that are indistinguishable from a dark
sky with stars, or night flying over a featureless terrain with a
clearly defined pattern of ground lights and a dark, starless sky
(Figure 12).
Vection Illusion: A common example is when you are stopped
at a traffic light in your car and the car next to you edges
forward. Your brain interprets this peripheral visual information
as though you are moving backwards and makes you apply
additional pressure to the brakes. A similar illusion can happen
while taxiing an aircraft (Figure 13).
How to Prevent Spatial Disorientation
• T ake the opportunity to personally experience sensory
illusions in a Baran y chair, a Vertigon, a GYRO, or a Virtual
Reality Spa tial Disorientation Demonstrator (VRSDD). By
experiencing sensor y illusions first-hand (on the ground),
pilots are better prepared to recognize a sensor y illusion
when it ha ppens during flight and to take immediate and
a ppropriate action. The Aerospace Medical Education Division
of the F AA Civil Aerospace Medical Institute offers spatial
disorienta tion demonstrations with the GYRO and the
VRSDD in Oklahoma City and a t all of the major airshows in
the continental U.S.
• Obtain training and maintain your proficienc y in aircraft
control by reference to instruments.
• When flying a t night or in reduced visibility, use and rely on
your flight instruments.
• Stud y and become familiar with unique geographical
conditions where flight is intended.
• Do not a ttempt visual flight when there is a possibility of
being tra pped in deteriorating weather.
• If you experience a visual illusion during flight (most pilots
do a t one time or another), have confidence in your
instruments and ignore all conflicting signals your bod y gives
you. Accidents usually happen as a result of a pilot’s
indecision to rely on the instruments.
• If you are one of two pilots in an aircraft and you begin to
experience a visual illusion, transfer control of the aircraft to the
other pilot, since pilots seldom experience visual illusions at the
same time.
• By being kno wledgeable, relying on experience, and trusting your
instruments, you will be contributing to keeping the skies safe
for ever yone.
Provided by
Aerospace Medical Education Division, AAM-400
To obtain copies of this brochure online:
https://www.faa.gov/pilots/safety/
pilotsafetybrochures/
or contact:
Federal Aviation Administration
Civil Aerospace Medical Institute
AAM-400
P.O. Box 25082
Oklahoma City, OK 73125
(405) 954-4831
Seeing Is Not Believing
Spatial Orientation
Our natural ability to maintain our body orientation and/or posture
in relation to the surrounding environment at rest and during
motion. Genetically speaking, humans are designed to maintain
spatial orientation on the ground. The flight environment is hostile
and unfamiliar to the human body; it creates sensory conflicts and
illusions that make spatial orientation difficult, and, in some cases,
even impossible to achieve. Statistics show that between 5 to
10% of all general aviation accidents can be attributed to spatial
disorientation, and 90% of these accidents are fatal.
Spatial Orientation on the Ground
Altitude DCS became a
commonly observed problem
associated with high-altitude
balloon and aircraft flights
in the 1930s. In present-day
aviation, technology allows
civilian aircraft (commercial
and private) to fly higher and
faster than ever before. Though
modern aircraft are safer and
more reliable, occupants are
still subject to the stresses of high altitude flight—and the unique
problems that go with these lofty heights. A century and one-half
after the first DCS case was described, our understanding of DCS has
improved, and a body of knowledge has accumulated; however, this
problem is far from being solved. Altitude DCS still represents a risk to
the occupants of modern aircraft.
Spatial Orientation In Flight
Spatial orientation in flight is sometimes difficult to achieve
because the various types of sensory stimuli (visual, vestibular,
and proprioceptive) vary in magnitude, direction, and frequency.
Any differences or discrepancies between visual, vestibular, and
proprioceptive sensory inputs result in a “sensory mismatch” that can
produce illusions and lead to spatial disorientation.
Vision and Spatial Orientation
Visual references provide the most important sensory information to
maintain spatial orientation on the ground and during flight, especially
when the body and/or the environment are in motion. Even birds,
reputable flyers, are unable to maintain spatial orientation and fly
safely when deprived of vision (due to clouds or fog). Only bats have
developed the ability to fly without vision by replacing their vision with
auditory echolocation. So, it should not be any surprise to us that,
when we fly under conditions of limited visibility, we have problems
maintaining spatial orientation.
Central Vision
Central vision, also known as foveal vision, is involved with the
identification of objects and the perception of colors. During
instrument flight rules (IFR) flights, central vision allows pilots to
acquire information from the flight instruments that is processed
by the brain to provide orientational information. During visual flight
rules (VFR) flights, central vision allows pilots to acquire external
information (monocular and binocular) to make judgments of distance,
speed, and depth.
Peripheral Vision
Peripheral vision, also known as ambient vision, is involved with the
perception of movement (self and surrounding environment) and
provides peripheral reference cues to maintain spatial orientation. This
capability enables orientation independent from central vision, and
that is why we can walk while reading. With peripheral vision, motion
of the surrounding environment produces a perception of self-motion
even if we are standing or sitting still.
Visual References
Visual references that provide information about distance, speed, and
depth of visualized objects include:
• Compara tive size of known objects at different distances.
• Compara tive form or shape of known objects at
different distances.
• Rela tive velocity of images moving across the retina. Nearby
objects are perceived as moving faster than distant objects.
• Interposition of kno wn objects. One object placed in front of
another is perceived as being c loser to the observer.
• V arying texture or contrast of known objects at different distances.
Object detail and contrast are lost with distance.
• Differences in illumina tion perspective of objects due to light
and shado ws.
• Differences in aerial perspective of visualized objects. More distant
objects are seen as bluish and blurr y.
The flight attitude of an airplane is generally determined by the pilot’s
visual reference to the natural horizon. When the natural horizon is
obscured, attitude can sometimes be maintained by visual reference
to the surface below. If neither horizon nor surface visual references
exist, the airplane’s attitude can only be determined by artificial
means such as an attitude indicator or other flight instruments.
Surface references or the natural horizon may at times become
obscured by smoke, fog, smog, haze, dust, ice particles, or other
phenomena, although visibility may be above VFR minimums. This is
especially true at airports located adjacent to large bodies of water or
sparsely populated areas, where few, if any, surface references are
available. Lack of horizon or surface reference is common on over-
water flights, at night, or in low visibility conditions.
Visual Illusions
Visual illusions are familiar to most of us. As children, we learned
that railroad tracks—contrary to what our eyes showed us—
don’t come to a point at the horizon. Even under conditions of
good visibility, you can experience visual illusions including:
Aerial Perspective Illusions may make you change (increase
or decrease) the slope of your final approach. They are caused
by runways with different widths, upsloping or downsloping
runways, and upsloping or downsloping final approach terrain.
Pilots learn to recognize a normal final approach by developing
and recalling a mental image of the expected relationship
between the length and the width of an average runway, such as
that exemplified in (Figure 1).
A final approach over a flat terrain with an upsloping runway
may produce the visual illusion of a high-altitude final approach.
If you believe this illusion, you may respond by pitching the
aircraft nose down to decrease the altitude, which, if performed
too close to the ground, may result in an accident (Figure 2).
A final approach over a flat terrain with a downsloping runway
may produce the visual illusion of a low-altitude final approach.
If you believe this illusion, you may respond by pitching the
aircraft nose up to increase the altitude, which may result in a
low-altitude stall or missed approach (Figure 3).
A final approach over an upsloping terrain with a flat runway
may produce the visual illusion that the aircraft is higher than
it actually is. If you believe this illusion, you may respond
by pitching the aircraft nose-down to decrease the altitude,
resulting in a lower approach. This may result in landing short
or flaring short of the runway and risking a low-altitude stall.
Pitching the aircraft nose-down will result in a low, dragged-
in approach. If power settings are not adjusted, you may find
yourself short of the runway, needing to add power to extend
your flare. If you do not compensate with power, you will land
short or stall short of the runway (Figure 4).
A final approach over a downsloping terrain with a flat
runway may produce the visual illusion that the aircraft is
lower than it actually is. If you believe this illusion, you may
respond by pitching the aircraft’s nose up to gain altitude. If
this happens, you will land further down the runway than you
intended (Figure 5).
A final approach to an unusually narrow runway or an
unusually long runway may produce the visual illusion of
being too high. If you believe this illusion, you may pitch the
aircraft’s nose down to lose altitude. If this happens too close
to the ground, you may land short of the runway and cause an
accident (Figure 6).
A final approach to an unusually wide runway may produce
the visual illusion of being lower than you actually are. If you
believe this illusion, you may respond by pitching the aircraft’s
nose up to gain altitude, which may result in a low-altitude
stall or missed approach (Figure 7).