民間航空機運航乗員の聴力

抄録

It is said that high frequency hearing loss is often found in commercial airline pilots. The cause was considered to be the radio communication sound of the Air Traffic Control. The pilots monitor the communication sound through a single earphone on one ear. Some reports have said captains tend to have hearing loss of the left ear, because they monitor the sound with the left ear. Co-pilots and flight engineers have problems with the right ear for the same reason.
The noise the pilots are exposed to is radio communication sound and cockpit noise of the aircraft. Flight engineers are further exposed to the noise on the airport apron during the exterior inspection. In this study, cockpit noise, cabin noise and exterior noise were analysed. The results were that none of them cause hearing loss at a high rate.
The special quality of the headset which the pilots use was also analysed. The sound pressure greatly changed according to the contact of the ear canal and the ear tip. At the condition of the opening is exist (between the ear canal and the ear tip) the sound pressure of the low frequencies tend to be low. The occurence and progress of hearing loss was thought to depend on the way the radio communication equipment was used.
Using audiograms recorded at periodic medical examinations in 1989 by certain airline, the hearing level and the frequency of hearing loss of right and left ears were analysed. 1937 pilots were classified by type of occupation (captain, co-pilot or flight engineer), age and flight time. The examination of the difference of the average of right and left ears' hearing level, difference of the frequency of c5dip, showed no statistically significant difference between right and left ears. Further the correlation of hearing level at 4, 000 Hz versus age, hearing level of 4, 000Hz versus flight time, hearing level of 4, 000Hz of the right ear versus the left ear were investigated. As the results showed the correlation of the hearing level versus age to be greater than versus flight time, the influence of aging is suggested. The correlation of the hearing level of right ear versus that of left ear was largest. The hearing of the right and left ears seemed to change similarly. Therefore the sound of radio communication cannot possively be the main cause of the hearing loss such as the difference of the individual tolerance to noise are more plausible.
1, 452 pilots, 388 cabin attendants and 1, 175 members of the general public were compared in age bracket groups for the hearing level and loss of high frequency hearing. In the same age groups, the hearing level and the rate of hearing loss of pilots and cabin attendants were almost same degree, but comparison with general pubic, showed the rate of hearing loss of the general public to be larger than that of pilots and cabin attendants. Furthermore, when the rate of high frequency hearing loss was compared between different types of pilot, the difference was not statistically significant. The hearing levels of pilots recorded in 1984 and 1989 were compared. The hearing level had not fallen during these five years. It was therefore shown that being a commercial airline pilot causes loss of hearing not so frequently.