Federal Aviation Administration Medical Facts for Pilots - Spatial Disorientation

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Federal Aviation Administration Medical Facts for Pilots - Spatial Disorientation - Visual Illusions, Złudzenia ...

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Spatial Disorientation
Visual Illusions
SPATIAL DISORIENTATION:
Seeing Is Not Believing
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.
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.
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.
Spatial Orientation on the Ground
Good spatial orientation on the ground relies on the
effective perception, integration, and interpretation of
visual, vestibular (organs of equilibrium located in the inner
ear), and proprioceptive (receptors located in the skin,
muscles, tendons, and
joints) sensory
information. Changes in
linear acceleration,
angular acceleration, and
gravity are detected by
the vestibular system and
the proprioceptive
receptors, and then
compared in the brain
with visual information
(Figure 1).
Figure 1
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.
OK-11-1550
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 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.
Visual References
Visual references that provide information about distance,
speed, and depth of visualized objects include:
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 2.
• Comparativesizeofknownobjectsatdifferentdistances.
• Comparativeformorshapeofknownobjectsatdifferent
distances.
• Relativevelocityofimagesmovingacrosstheretina.
Nearby objects are perceived as moving faster than
distant objects.
Figure 2
• Interpositionofknownobjects.Oneobjectplacedin
front of another is perceived as being closer to the
observer.
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 3).
• Varying texture or contrast of known objects at different
distances. Object detail and contrast are lost with distance.
• Differencesinilluminationperspectiveofobjectsdueto
light and shadows.
• Differencesinaerialperspectiveofvisualizedobjects.
More distant objects are seen as bluish and blurry.
Figure 3
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.
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 4).
Figure 4
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 5).
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 8).
Figure 8
Figure 5
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 9,
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 10) you can easily orient yourself correctly
using your central vision.
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 6).
Figure 9
Figure 6
Figure 10
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 7).
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 11).
Figure 11
Figure 7
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 12).
How to Prevent Spatial Disorientation
• Taketheopportunitytopersonallyexperiencesensory
illusions in a Barany chair, a Vertigon, a GYRO, or a
Virtual Reality Spatial Disorientation Demonstrator
(VRSDD). By experiencing sensory illusions first-hand
(on the ground), pilots are better prepared to recognize a
sensory illusion when it happens during flight and to
take immediate and appropriate action. The Aerospace
Medical Education Division of the FAA Civil Aerospace
Medical Institute offers spatial disorientation
demonstrations with the GYRO and the VRSDD in
Oklahoma City and at all of the major airshows in the
continental U.S.
• Obtaintrainingandmaintainyourproficiencyinaircraft
control by reference to instruments.
• Whenflyingatnightorinreducedvisibility,useandrely
on your flight instruments.
• Studyandbecomefamiliarwithuniquegeographical
conditions where flight is intended.
• Donotattemptvisualflightwhenthereisapossibilityof
being trapped in deteriorating weather.
• Ifyouexperienceavisualillusionduringflight(most
pilots do at one time or another), have confidence in
your instruments and ignore all conflicting signals your
body gives you. Accidents usually happen as a result of a
pilot’s indecision to rely on the instruments.
• Ifyouareoneoftwopilotsinanaircraftandyoubegin
to experience a visual illusion, transfer control of the
aircraft to the other pilot, since pilots seldom experience
visual illusions at the same time.
• Bybeingknowledgeable,relyingonexperience,and
trusting your instruments, you will be contributing to
keeping the skies safe for everyone.
Figure 12
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 13).
Figure 13
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 14).
Medical Facts for Pilots
Publication AM-400-00/1 (rev. 2/11)
Revised by: Melchor J. Antuñano, M.D.
FAA Civil Aerospace Medical Institute
To request copies, contact:
FAA Civil Aerospace Medical Institute
Shipping Clerk, AAM-400
P.O. Box 25082 Oklahoma City, OK 73125
(405) 954-4831
A complete list of pilot safety brochures
is on the FAA Web site:
www.faa.gov/pilots/safety/pilotsafetybrochures/
Figure 14
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