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Pilot's Handbook of Aeronautical Knowledge
Aeromedical Factors

Health and Physiological Factors Affecting Pilot Performance

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Human sensation of angular acceleration.
Figure 16-4. Human sensation of angular acceleration.

Under normal flight conditions, when there is a visual
reference to the horizon and ground, the sensory system in the
inner ear helps to identify the pitch, roll, and yaw movements
of the aircraft. When visual contact with the horizon is lost,
the vestibular system becomes unreliable. Without visual
references outside the aircraft, there are many situations in
which combinations of normal motions and forces create
convincing illusions that are difficult to overcome.

Prevention is usually the best remedy for spatial disorientation.
Unless a pilot has many hours of training in instrument flight,
flight should be avoided in reduced visibility or at night when
the horizon is not visible. A pilot can reduce susceptibility
to disorienting illusions through training and awareness, and
learning to rely totally on flight instruments.

Vestibular Illusions
The Leans

A condition called the leans can result when a banked
attitude, to the left for example, may be entered too slowly
to set in motion the fluid in the "roll" semicircular tubes.
[Figure 16-4] An abrupt correction of this attitude sets the
fluid in motion, creating the illusion of a banked attitude to the
right. The disoriented pilot may make the error of rolling the
aircraft into the original left banked attitude, or if level flight
is maintained, will feel compelled to lean in the perceived
vertical plane until this illusion subsides.

Coriolis Illusion
The coriolis illusion occurs when a pilot has been in a turn
long enough for the fluid in the ear canal to move at the same
speed as the canal. A movement of the head in a different
plane, such as looking at something in a different part of the
flight deck, may set the fluid moving and create the illusion
of turning or accelerating on an entirely different axis.
This action causes the pilot to think the aircraft is doing a
maneuver that it is not. The disoriented pilot may maneuver
the aircraft into a dangerous attitude in an attempt to correct
the aircraft's perceived attitude.

For this reason, it is important that pilots develop an instrument
cross-check or scan that involves minimal head movement.
Take care when retrieving charts and other objects in the flight
deckā€”if something is dropped, retrieve it with minimal head
movement and be alert for the coriolis illusion.

Graveyard Spiral
As in other illusions, a pilot in a prolonged coordinated,
constant-rate turn, will have the illusion of not turning.
During the recovery to level flight, the pilot will experience
the sensation of turning in the opposite direction. The
disoriented pilot may return the aircraft to its original turn.
Because an aircraft tends to lose altitude in turns unless the
pilot compensates for the loss in lift, the pilot may notice
a loss of altitude. The absence of any sensation of turning
creates the illusion of being in a level descent. The pilot may
pull back on the controls in an attempt to climb or stop the
descent. This action tightens the spiral and increases the loss
of altitude; this illusion is referred to as a graveyard spiral.
[Figure 16-5] At some point, this could lead to a loss of
aircraft control.

Graveyard spiral.
Figure 16-5. Graveyard spiral.