Medical Handbook For Pilots Chapter 17 – Noise

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.

Aeronautical engineers have attempted to cut down aircraft noise at the sources, but the loss of power remains a mechanical dilemma. Mufflers on the exhausts 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 the 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 unavoidably 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.

High-pitched sounds 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 beginninng 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.