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Instrument Flying Handbook
Human factors
illusions Leading to Spatial Disorientation

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

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.

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 1-8] These situations include uncoordinated turns,
climbing turns, and turbulence.

Demonstration of Spatial Disorientation
There are a number of controlled aircraft maneuvers a pilot
can perform to experiment with spatial disorientation. While
each maneuver will normally create a specific illusion, any
false sensation is an effective demonstration of disorientation.
Thus, even if there is no sensation during any of these
maneuvers, the absence of sensation is still an effective
demonstration in that it shows the inability to detect bank
or roll. There are several objectives in demonstrating these
various maneuvers.

1. They teach pilots to understand the susceptibility of
the human system to spatial disorientation,

2. They demonstrate that judgments of aircraft attitude
based on bodily sensations are frequently false.

3. They help lessen the occurrence and degree of
disorientation through a better understanding of the
relationship between aircraft motion, head movements,
and resulting disorientation.

4. They help instill a greater confidence in relying on
flight instruments for assessing true aircraft attitude.

Sensations From Centrifugal Force.
Figure 1-8. Sensations From Centrifugal Force.