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replaced by “in all things, moderation.”
Just Do It!
Physical fitness is a proven
component of a long and
healthy life. Physical fitness
can also prolong your aviation
activities by helping you pass
your flight physicals.
MEDICAL FACTS FOR PILOTS
Publication No. AM-400/09/2
Written by:
J.R. Brown
Federal Aviation Administration
Civil Aerospace Medical Institute
To request copies of this brochure, contact:
FAA Civil Aerospace Medical Institute
Shipping Clerk, AAM-400
P.O. Box 25082
Oklahoma City, OK 73125
(405) 954-4831
Physiological Training Classes for Pilots
If you are interested in taking a one-day aviation physiological
training course with altitude chamber and vertigo demonstrations
or a one-day survival course, learn about how to sign up for these
courses that are offered at 14 locations across the U.S. by visiting
this FAA Web site:
www.faa.gov/pilots/training/airman_education/aerospace_
physiology/index.cfm
1
HEARING AND NOISE IN
AVIATION
HEARING
The term hearing describes the process,
function, or power of perceiving sound.
Hearing is second only to vision as a
physiological sensory mechanism to obtain critical
information during the operation of an aircraft. The
sense of hearing makes it possible to perceive,
process, and identify among the myriad of sounds
from the surrounding environment.
Anatomy and Physiology of the
Auditory System
The auditory
system
consists of
the external
ear, ear canal,
eardrum,
auditory
ossicles,
cochlea (which
resembles a
snail shell and is fi lled with fl uid), and the auditory
nerve.
Ambient sound waves are collected by the external
ear, conducted through the ear canal, and cause
the eardrum to vibrate. Eardrum vibration is
mechanically transmitted to the ossicles, which, in
turn, produce vibration of a fl exible window in the
cochlea. This vibration causes a pressure wave
in the fl uid located inside the cochlea, moving
thousands of hair-like sensory receptors lining the
inner walls of the cochlea. The movement of these
receptors resembles the gentle movement of a
crop fi eld caused by the wind. The stimulation of
these sensors produces an electrical signal that is
transmitted to the brain by the auditory nerve. This
signal is then processed by the brain and identifi ed
as a particular type of sound.
SOUND
The term sound is used to describe the mechanical
radiant energy that is transmitted by longitudinal
pressure waves in a medium (solid, liquid, or gas).
Sound waves are variations in air pressures above
and below the ambient pressure. From a more
practical point of view, this term describes the
sensation perceived by the sense of hearing. All
sounds have three distinctive variables: frequency,
intensity, and duration.
Frequency. This is the physical property of sound
that gives it a pitch. Since sound energy propagates
in a wave-form, it can be measured in terms of wave
oscillations or wave cycles per second, known as
hertz (Hz). Sounds that are audible to the human
ear fall in the frequency range of about 20-20,000
Hz, and the highest sensitivity is between 500 and
4,000 Hz. Sounds below 20 Hz and above 20,000
Hz cannot be perceived by the human ear. Normal
conversation takes place in the frequency range
from 500 to 3,000 Hz.
Intensity. The correlation between sound intensity
and loudness. The decibel (dB) is the unit used
to measure sound intensity. The range of normal
hearing sensitivity of the human ear is between
-10 to +25 dB. Sounds below -10dB are generally
imperceptible. A pilot who cannot hear a sound
unless its intensity is higher than 25 dB (at any
frequency) is already experiencing hearing loss.
Duration. Determines the quality of the perception
and discrimination of a sound, as well as the
potential risk of hearing impairment when exposed
to high intensity sounds. The adverse consequences
of a short-duration exposure to a loud sound can be
as bad as a long-duration exposure to a less intense
sound. Therefore, the potential for causing hearing
damage is determined not only by the duration of a
sound but also by its intensity.
NOISE
The term noise refers to a sound, especially one
which lacks agreeable musical quality, is noticeably
unpleasant, or is too loud. In other words, noise is
2
any unwanted or annoying sound. Categorizing a
sound as noise can be very subjective. For example,
　
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