FAA Brochure - Spatial Disorientation

Spatial

Disorientation

Visual Illusions

OK-24-1154 9/18/2024A 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).