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AIM 

4/20/23

 

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Fitness for Flight

b. Illusions Leading to Spatial Disorientation.

1.

Various complex motions and forces and certain visual scenes encountered in flight can create illusions

of motion and position. Spatial disorientation from these illusions can be prevented only by visual reference to
reliable, fixed points on the ground or to flight instruments.

2. The leans.

An abrupt correction of a banked attitude, which has been entered too slowly to stimulate

the motion sensing system in the inner ear, can create the illusion of banking in the opposite direction. The
disoriented pilot will roll the aircraft back into its original dangerous attitude, or if level flight is maintained, will
feel compelled to lean in the perceived vertical plane until this illusion subsides.

(a) Coriolis illusion.

An abrupt head movement in a prolonged constant-rate turn that has ceased

stimulating the motion sensing system can create the illusion of rotation or movement in an entirely different axis.
The disoriented pilot will maneuver the aircraft into a dangerous attitude in an attempt to stop rotation. This most
overwhelming of all illusions in flight may be prevented by not making sudden, extreme head movements,
particularly while making prolonged constant-rate turns under IFR conditions.

(b) Graveyard spin.

A proper recovery from a spin that has ceased stimulating the motion sensing

system can create the illusion of spinning in the opposite direction. The disoriented pilot will return the aircraft
to its original spin.

(c) Graveyard spiral.

An observed loss of altitude during a coordinated constant-rate turn that has

ceased stimulating the motion sensing system can create the illusion of being in a descent with the wings level.
The disoriented pilot will pull back on the controls, tightening the spiral and increasing the loss of altitude.

(d) Somatogravic illusion.

A rapid acceleration during takeoff can create the illusion of being in a nose

up attitude. The disoriented pilot will push the aircraft into a nose low, or dive attitude. A rapid deceleration by
a quick reduction of the throttles can have the opposite effect, with the disoriented pilot pulling the aircraft into
a nose up, or stall attitude.

(e) Inversion illusion.

An abrupt change from climb to straight and level flight can create the illusion

of tumbling backwards. The disoriented pilot will push the aircraft abruptly into a nose low attitude, possibly
intensifying this illusion.

(f) Elevator illusion.

An abrupt upward vertical acceleration, usually by an updraft, can create the

illusion of being in a climb. The disoriented pilot will push the aircraft into a nose low attitude. An abrupt
downward vertical acceleration, usually by a downdraft, has the opposite effect, with the disoriented pilot pulling
the aircraft into a nose up attitude.

(g) False horizon.

Sloping cloud formations, an obscured horizon, a dark scene spread with ground

lights and stars, and certain geometric patterns of ground light can create illusions of not being aligned correctly
with the actual horizon. The disoriented pilot will place the aircraft in a dangerous attitude.

(h) Autokinesis.

In the dark, a static light will appear to move about when stared at for many seconds.

The disoriented pilot will lose control of the aircraft in attempting to align it with the light.

3. Illusions Leading to Landing Errors.

(a)

Various surface features and atmospheric conditions encountered in landing can create illusions of

incorrect height above and distance from the runway threshold. Landing errors from these illusions can be
prevented by anticipating them during approaches, aerial visual inspection of unfamiliar airports before landing,
using electronic glide slope or VASI systems when available, and maintaining optimum proficiency in landing
procedures.

(b) Runway width illusion.

A narrower-than-usual runway can create the illusion that the aircraft is at

a higher altitude than it actually is. The pilot who does not recognize this illusion will fly a lower approach, with
the risk of striking objects along the approach path or landing short. A wider-than-usual runway can have the
opposite effect, with the risk of leveling out high and landing hard or overshooting the runway.