Somatogravic Illusion
A rapid acceleration, such as experienced during takeoff,
stimulates the otolith organs in the same way as tilting the
head backwards. This action creates the somatogravic illusion
of being in a nose-up attitude, especially in situations without
good visual references. The disoriented pilot may push the
aircraft into a nose-low or dive attitude. A rapid deceleration
by quick reduction of the throttle(s) can have the opposite
effect, with the disoriented pilot pulling the aircraft into a
nose-up or stall attitude.

Inversion Illusion
An abrupt change from climb to straight-and-level flight can
stimulate the otolith organs enough to create the illusion of
tumbling backwards, or inversion illusion. The disoriented
pilot may push the aircraft abruptly into a nose-low attitude,
possibly intensifying this illusion.

Elevator Illusion
An abrupt upward vertical acceleration, as can occur in
an updraft, can stimulate the otolith organs to create the
illusion of being in a climb. This is called elevator illusion.
The disoriented pilot may push the aircraft into a nose-low
attitude. An abrupt downward vertical acceleration, usually
in a downdraft, has the opposite effect, with the disoriented
pilot pulling the aircraft into a nose-up attitude.

Visual Illusions
Visual illusions are especially hazardous because pilots rely
on their eyes for correct information. Two illusions that lead
to spatial disorientation, false horizon and autokinesis, are
concerned with only the visual system.

False Horizon
A sloping cloud formation, an obscured horizon, an aurora
borealis, a dark scene spread with ground lights and stars,
and certain geometric patterns of ground lights can provide
inaccurate visual information, or false horizon, for aligning
the aircraft correctly with the actual horizon. The disoriented
pilot may place the aircraft in a dangerous attitude.

Autokinesis
In the dark, a stationary light will appear to move about when
stared at for many seconds. The disoriented pilot could lose
control of the aircraft in attempting to align it with the false
movements of this light, called autokinesis.

Postural Considerations
The postural system sends signals from the skin, joints, and
muscles to the brain that are interpreted in relation to the
Earth's gravitational pull. These signals determine posture.
Inputs from each movement update the body's position to
the brain on a constant basis. "Seat of the pants" flying is
largely dependent upon these signals. Used in conjunction
with visual and vestibular clues, these sensations can be
fairly reliable. However, because of the forces acting upon
the body in certain flight situations, many false sensations
can occur due to acceleration forces overpowering gravity.
[Figure 16-6] These situations include uncoordinated turns,
climbing turns, and turbulence.