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engines (piston, turbo-prop, turbo-jet, turbo-fan) but also considerably on aerodynamic noise and the speed of
the aircraft. The basic problem is the effect of flight-deck noise upon speech perception, i.e. speech
interference levels. It is complicated by acoustically significant differences in the use of earphones or overhead
speakers for listening to R/T signals. Earphones are often not designed for hearing protection, thus little sound
attenuation is provided. Whether earphones or loudspeakers are used on the flight deck, the signal-to-ambient
noise ratio can be varied through volume control.
As the speech-in-noise test is relevant for the final assessment of auditory fitness for applicants who have
failed to meet the pure-tone audiometry requirements, these tests, as well as practical assessment in flight if
necessary, should be carried out so as to produce reliable results and to convey confidence on an international
basis, considering their importance for flight safety. An applicant who fails to pass the pure-tone audiometry
test should not be declared unfit because of hearing loss, if his speech and signal perception has been
demonstrated to be within acceptable limits at the appropriate masking noise level.
The background noise, regulated at the desired intensity levels, can be presented to the ear on separate
loudspeakers. The volume of the test material should be controllable by the applicant in a manner
representative of the aircraft communication equipment.
ICAO Preliminary Unedited Version — October 2008 III-12-20
TYPES OF HEARING LOSS
Monaural Hearing Loss
The risk of sudden loss of hearing during flight is negligible. Head-shadow effects, brought about by the head
in certain positions, cause poorer discrimination during monaural reception and might affect efficient
communication between crew members and should be taken into account. The question of whether the
affected individual is a pilot-in-command or co-pilot is relevant because of the seating arrangements. The
differences in signal-to-noise ratio necessary for equivalent monaural and binaural perception are usually 3-4
dB. Annex 1, 6.3.4.1 and 6.5.4.1, specify a hearing ability "in each ear separately". In addition, 6.3.2.25
requires an applicant to “not possess any abnormality or disease of the ear”. Monaural hearing in both private
pilots and professional flight crews should therefore always be investigated and evaluated in accordance with
best medical practice as well as assessed under 6.3.4.1.1. It should be noted that under the provisions of Annex
6, multi-crew aircraft are required to have intercom and radio equipment which can be effectively used in these
cases.
Individuals with monaural loss complain about their inability to localize sound, to understand speech in noisy
situations, and to hear or understand speech directed to their poor side (shadowing). A so-called
CROS-arrangement - contralateral renting of the signal - may sometimes be used advantageously for the
person with normal hearing in one ear and essentially no hearing in the other ear. Here the auditory signals are
picked up by a microphone placed beside the poor ear and shunted across, either electrically or acoustically, to
the good ear. A non-occluding-type ear mould is used in the good ear which permits the direct reception of
auditory stimuli in that ear. Persons fitted with this arrangement report a decided improvement in their ability
to understand speech directed to their bad ear as well as some improvement in their ability to understand
speech in noisy situations.
Presbyacusis
As a pilot grows older, there will be a gradual deterioration of hearing. This sensorineural hearing loss is called
presbyacusis. The age of onset of presbyacusis may occur as early as the thirties and Figure 12-4 shows the
high frequency hearing loss synonymous with the aging process. Repeat audiograms will detect the situation.
The vast majority of individuals with sensorineural hearing impairment can gain significant improvement
through the use of a wearable hearing aid.
ICAO Preliminary Unedited Version — October 2008 III-12-21
Fig. 12-4: Audiogram showing presbyacusis
HEARING AIDS
Few applicants present themselves for a medical examination wearing a hearing aid. There are, however, quite
a number of flight crew who can benefit, particularly socially, by an aid. When an applicant can communicate
better with the hearing aid than without it, consideration should be given for its use for aviation duties on the
ground.
The first hearing aids were made in the late 1920s and early 1930s. These carbon-type aids were responsible
for the prevalent notion that only persons with conductive hearing loss could benefit from hearing aids.
　
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本文鏈接地址：Manual of Civil Aviation Medicine 2(84)