Noise has always been
accepted as one of the prices to be paid for the pleasure and
convenience of flying. However, if you are not armed with the knowledge
of certain facts about aircraft noise, the price may be high. Your
hearing may become permanently impaired.
have attempted to cut down aircraft noise at the sources, but the loss
of power remains a mechanical dilemma. Mufflers on the exhaust of jet
and reciprocating engines illustrate the success of sound reduction at
the sacrifice of power. Propeller blades, the second main noise source,
create a tremendous sound buildup when their tips reach a speed near
Mach 1. This sound buildup can be lessened only by slowing the
propellers thereby reducing power.
Other noise sources also
pose problems for the pilot and his passengers. In jet aircraft, airflow
noise is considerable although it diminishes with altitude. In
helicopters the cockpit is often poorly sealed or it is flown with doors
and windows open, exposing the occupants to intense noise from the
engine, rotor blades, and rotor transmission assemblies.
The main concern about
noise is its long-term effect on hearing. Short-term impairment of
hearing after a flight is common and usually benign. It is the gradual
deterioration of hearing that you must guard against.
No set rules can be
given about such hearing loss. Individuals vary widely in their response
to the same noise for the same length of time. After a 6 to 8 hour
cruise in a light aircraft, you are likely to experience a slight
hearing loss, with full recovery within 1 to 2 hours. The much louder
noise of a jet engine may cause very rapid hearing fatigue, often within
a few minutes. Under these conditions, your ears may require anywhere
from several hours to several days for full recovery. In some severe
cases, the damage is permanent.
The annoyance, fatigue,
interference with speech, and hearing losses caused by noise depend a
good deal upon its frequency, or "pitch" (measured in cycles per second)
and upon its "loudness" or intensity (measured in decibels). No matter
how loud the noise, sounds of low pitch are much less annoying than
sounds of high pitch. Reciprocating engines tend to produce loud noises
mostly in lower pitches, and so are more tolerable than jet engines,
which produce sounds of high, medium, and low pitches simultaneously.
Fortunately, cockpits are usually located in areas where noise intensity
is tolerable during cruise (85 to 95 decibels). However, as a pilot, you
are an avoidably exposed to steady noise for long periods of time and
for many years of your life - noise often sufficient to diminish the
acuity of your hearing.
constitute the greatest hazard of aircraft noise, because they are most
likely to produce both temporary and permanent damage to the fine,
hair-like cells of the inner ear structures. This, in turn, leads to
progressive and, finally, irreversible deafness. Fortunately, you can
minimize this danger by the use of ear defenders (plugs, muffs, etc.),
which tend to damp out the higher pitched sounds without interfering
with the sounds needed for communications and navigation.
The first signs of
permanent deterioration of hearing can be detected only by special
testing with an audiometer in the frequency ranges which are above the
pitch of the human voice. You may be able to hear conversation quite
well and not even be aware of any hearing loss due to noise, unless you
are specifically tested. Eventually, however, the permanent loss may
move down into the voice frequency range unless you take steps to
protect yourself against further deterioration.
With increasing age, a
certain degree of "normal" deterioration in hearing can be detected by
careful testing and should not be a cause for alarm. If repeated testing
at intervals reveals a loss more rapid than your physician considers
normal, he can advise you of suitable precautions to observe.
Some simple tips will
help you guard against hearing loss:
1. Use ear defenders (such as plugs or muffs) whenever possible.
Plugs will actually improve your hearing in a noisy environment with no
sacrifice of acuity.
2. Protect yourself against any noise which produces pain in the
ears. This signals the beginning of damage to the delicate structures
within the ear.
3. Avoid unnecessary exposure to all noise. Lower the volume on
your earphones or speaker when possible, especially the tone signals of
navigational aids and heavy static.