SPATIAL DISORIENTATION
Acknowledgements: FAA
Safety Team (FAAST)
What Is It?
Sight, supported by other senses,
allows a pilot to maintain orientation while flying. However, when visibility
is restricted (i.e., no visual reference to the horizon or surface detected)
the body’s supporting senses can conflict with what is seen.
When this spatial
disorientation occurs, sensory conflicts and optical illusions often make it difficult for a
pilot to tell which way is up.
Contributing to these
phenomena are the various types of sensory stimuli: visual, vestibular (organs
of equilibrium located in the inner ear), and proprioceptive (receptors located
in the skin, muscles, tendons and joints). 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.
In a flight environment, these
stimuli can vary in magnitude, direction, and frequency, resulting in a
“sensory mismatch” which can produce illusions and lead to spatial disorientation.
Some of these illusions can lure pilots in to making poor decisions or improper
control inputs.
For example, aerial perspective illusions may make you increase or
decrease the slope of your final approach. They are caused by runways with different
widths, up-sloping or down-sloping runways, and up-sloping or down-sloping final
approach terrain.
NTSB accident data suggests
that spatial disorientation may be a precursor to many general
aviation accidents - particularly in night or limited visibility weather conditions.
Instrument and VFR pilots are both vulnerable to spatial disorientation and
optical illusions which may cause loss of aircraft control.
An auto-kinetic 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.
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.
How to Prevent Spatial
Disorientation
You, the pilot, should understand
the elements contributing to spatial disorientation so as to prevent loss of
aircraft control if these conditions are inadvertently encountered.
The following steps should
help prevent spatial disorientation:
·
Before you fly with less than
3 miles of visibility, obtain training and maintain proficiency at flying by instruments.
·
At night, or with reduced visibility,
use and rely on your flight instruments. Be
sure to test your flight instruments before each flight as well during your pre-flight
and taxi.
·
Maintain night currency if you intend to fly at night.
Include cross-country and local operations at different airports.
·
Study and become familiar with unique geographical
conditions in areas in which you plan to operate.
·
Check weather forecasts before
departure, en-route, and at destination. Be alert for weather
deterioration.
·
Do not attempt VFR flight when there is the possibility
of getting trapped in deteriorating weather.
·
If you experience a visual illusion during flight
(most pilots do at one me 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 over relying 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 me.
·
If you fly
single-engine IFR frequently, consider investment in an alternate vacuum system or electric standby attitude
indicator.
By being knowledgeable, relying on experience, and trusting your
instruments, you will be contributing to keeping the skies safe for everyone.
FLY SAFE!