Health Effects of Prolonged Exposure to High Noise Levels

Hearing loss is demonstrated by a threshold shift in an audiogram. A threshold shift means a pilot cannot discriminate among sounds in certain frequency ranges on the audiogram until the loudness is increased (i.e.shifted) above the control level. The medical profession defines hearing impairment as a threshold shift of 15 dB. An early study found that airline pilot hearing loss increased with age and logged flight time, and that the loss was greater than that experienced in the normal population. Because the FAA does not require audiograms for pilots there is little data on noise related hearing loss in pilots flying for United States carriers.

In the Netherlands, where pilots are required to have audiograms, 5% of pilots had mild to moderate hearing loss associated with exposure to chronic noise. Even among pilots with impaired hearing there was no discernible loss in the ability to understand routine ATC transmissions. Experience and familiarity with the pattern of transmissions allowed pilots to fill in the gaps and perform normally, as the FAA predicted. This shows that hearing loss may be more profound than the pilot realizes, because he does not perceive any difficulties at work due to hearing loss. Even pilots who do not demonstrate permanent hearing loss on an audiogram may experience temporary hearing loss because of exposure to noise at work. Temporary hearing loss could result in difficulty hearing cockpit communications or audio warnings.

Hearing damage caused by exposure to high noise levels is insidious, with effects that develop slowly over many years. Employees suffering hearing damage may not recognize symptoms, and may even deny that they exist. If hearing loss rates in the Netherlands correlate to the rate of hearing loss in the United States, more than 2,500 airline pilots have functional hearing loss attributable to noise.

High noise levels can have effects beyond making communication difficult and causing hearing loss. Researchers have noted impaired concentration, fatigue, and insomnia. Psychological responses to noise include irritability, anger, and anxiety. It is difficult to isolate health effects that are related to noise, since the noisy, hot (or cold), vibrating, cramped cockpit is a "stressor rich" environment. However, unlike the size and motion of the cockpit, the noise level in the cockpit can be addressed inexpensively.