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loud rock music can be described as an enjoyable
sound by some (usually teenagers), and at the same
time described as noise by others (usually adults).
Sources of Noise in Aviation. The aviation
environment is characterized by multiple sources of
noise, both on the ground and in the air. Exposure
of pilots to noise became an issue following the
introduction of the fi rst powered aircraft by the
Wright Brothers, and has been a prevalent problem
ever since. Noise is produced by aircraft equipment
powerplants, transmission systems, jet effl ux,
propellers, rotors, hydraulic and electrical actuators,
cabin conditioning and pressurization systems,
cockpit advisory and alert systems, communications
equipment, etc. Noise can also be caused by
the aerodynamic interaction between ambient air
(boundary layer) and the surface of the aircraft
fuselage, wings, control surfaces, and landing
gear. These auditory inputs allow pilots to assess
and monitor the operational status of their aircraft.
All pilots know the sounds of a normal-functioning
aircraft. On the other hand, unexpected sounds
or the lack of them, may alert pilots to possible
malfunctions, failures, or hazards. Every pilot has
experienced a cockpit or cabin environment that was
so loud that it was necessary to shout to be heard.
These sounds not only make the work environment
more stressful but can, over time, cause permanent
hearing impairment. However, it is also important
to remember that individual exposure to noise is a
common occurrence away from the aviation working
environment—at home or work, on the road, and in
public areas. The effects of pre-fl ight exposure to
noise can adversely affect pilot in-fl ight performance.
Sources of Sound/Noise
SOURCES LEVEL (dB)
Whispered Voice 20-30
Urban Home, Average Offi ce 40-60
Average Male Conversation 60-65
Noisy Offi ce, Low Traffi c Street 60-80
Jet Transports (Cabin) 60-88
Small Single Plane (Cockpit) 70-90
Public Address (PA) Systems 90-100
Busy City Street 80-100
Single Rotor Helicopter (Cockpit) 80-102
Power Lawn Mower, Chain Saw 100-110
Snowmobile, Thunder 110-120
Rock Concert 115-120
Jet Engine (Proximity) 130-160
Types of Noise
Steady: Continuous noise of sudden or gradual
onset and long duration (more than 1 second).
Examples: aircraft powerplant noise, propeller noise,
and pressurization system noise. According to the
Occupational Safety and Health Administration
(OSHA), the maximum permissible continuous
exposure level to steady noise in a working
environment is 90 dB for 8 hours.
Impulse/blast: Noise pulses of sudden onset and
brief duration (less than 1 second) that usually
exceed an intensity of 140dB. Examples: fi ring a
handgun, detonating a fi recracker, backfi ring of
a piston engine, high-volume squelching of radio
equipment, and a sonic boom caused by breaking
the sound barrier. The eardrum may be ruptured by
intense levels (140dB) of impulse/blast noise.
EFFECTS OF NOISE EXPOSURE
Physiologic
• Ear discomfort: May occur during exposure to a
120 dB noise.
• Ear pain: May occur during exposure to a 130 dB
noise.
• Eardrum rupture: May occur during exposure to a
140 dB) noise.
• Temporary hearing impairment. Unprotected
exposure to loud, steady noise over 90 dB for a
short time, even several hours, may cause hearing
impairment. This effect is usually temporary and
hearing returns to normal within several hours
following cessation of the noise exposure.
• Permanent hearing impairment: Unprotected
exposure to loud noise (higher than 90dB) for
eight or more hours per day for several years,
may cause a permanent hearing loss. Permanent
hearing impairment occurs initially in the vicinity
of 4,000 Hz (outside the conversational range)
and can go unnoticed by the individual for some
time. It is also important to remember that hearing
sensitivity normally decreases as a function of age
at frequencies from 1,000 to 6,000 Hz, beginning
around age 30.
3
Psychologic
• Subjective effects: Annoying high-intensity
noise can cause distraction, fatigue, irritability,
startle responses, sudden awakening and poor
sleep quality, loss of appetite, headache, vertigo,
nausea, and impair concentration and memory.
• Speech interference: Loud noise can interfere
with or mask normal speech, making it diffi cult to
understand.
• Performance: Noise is a distraction and can
increase the number of errors in any given task.
　
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