Aeronautica

Chapter 1

Human
Factors
Introduction
Human factors is a broad field that examines the interaction
between people, machines, and the environment for the
purpose of improving performance and reducing errors. As
aircraft became more reliable and less prone to mechanical
failure, the percentage of accidents related to human factors
increased. Some aspect of human factors now accounts forover 80 percent of all accidents. Pilots who have a good
understanding of human factors are better equipped to plan
and execute a safe and uneventful flight.
Flying in instrument meteorological conditions (IMC) can
result in sensations that are misleading to the body’s sensory
system. A safe pilot needs to understand these sensations and
effectively counteract them. Instrument flyingrequires a pilot
to make decisions using all available resources.
The elements of human factors covered in this chapter
include sensory systems used for orientation, illusions in
flight, physiological and psychological factors, medical
factors, aeronautical decision-making, and crew resource
management (CRM).

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Sensory Systems for Orientation
Orientation is the awareness of the positionof the aircraft
and of oneself in relation to a specific reference point.
Disorientation is the lack of orientation, and spatial
disorientation specifically refers to the lack of orientation
with regard to position in space and to other objects.
Orientation is maintained through the body’s sensory organs
in three areas: visual, vestibular, and postural. The eyes
maintain visual orientation.The motion sensing system in
the inner ear maintains vestibular orientation. The nerves in
the skin, joints, and muscles of the body maintain postural
orientation. When healthy human beings are in their natural
environment, these three systems work well. When the
human body is subjected to the forces of flight, these senses
can provide misleading information. It is this misleadinginformation that causes pilots to become disoriented.
Eyes
Of all the senses, vision is most important in providing
information to maintain safe flight. Even though the
human eye is optimized for day vision, it is also capable
of vision in very low light environments. During the day,
the eye uses receptors called cones, while at night, vision is
facilitated by the use of rods.
Both of these providea level
of vision optimized for the
lighting conditions that they
were intended. That is, cones
are ineffective at night and
rods are ineffective during
the day.
Rods, which contain rhodopsin
(called visual purple), are
especially sensitive to light
and increased light washes out
the rhodopsin compromising
the night vision. Hence, when
strong light is momentarily
introduced atnight, vision
may be totally ineffective as
the rods take time to become
effective again in darkness.
Smoking, alcohol, oxygen
deprivation, and age affect
vision, especially at night. It
should be noted that at night,
oxygen deprivation such as one
caused from a climb to a high
altitude causes a significant
reduction in vision. A return
back to the lower altitude will
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not restore apilot’s vision in the same transitory period used
at the climb altitude.
The eye also has two blind spots. The day blind spot is the
location on the light sensitive retina where the optic nerve
fiber bundle (which carries messages from the eye to the
brain) passes through. This location has no light receptors,
and a message cannot be created there to be sent to the brain.
The night blindspot is due to a concentration of cones in an
area surrounding the fovea on the retina. Because there are
no rods in this area, direct vision on an object at night will
disappear. As a result, off-center viewing and scanning at
night is best for both obstacle avoidance and to maximize
situational awareness. [See the Pilot’s Handbook of
Aeronautical Knowledge and the Aeronautical Information...