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levels. Pure tone audiometry should be carried out in a quiet room in which the background noise intensity is
less than 35 dB(A), i.e. measured on "slow" response of an "A"-weighted sound-level meter (Annex 1, 6.2.5,
Note 2).
ICAO Preliminary Unedited Version — October 2008 III-12-17
Hearing requirements for Class 1 and Class 3 Medical Assessments require an applicant tested on a pure-tone
audiometer not to have "a hearing loss, in either ear separately, of more than 35 dB at any of the frequencies
500, 1 000 or 2 000 Hz, or more than 50 dB at 3 000 Hz".
Speech audiometry
A speech audiometer is essentially the same instrument as the pure-tone audiometer. It produces the spoken
voice rather than pure tones at controlled intensity levels. The spoken voice may be a "live voice" but is
normally a recorded voice, preferably by a selected speaker (air traffic controller). Speech audiometry is
basically a speech intelligibility test. The percentage of words correctly perceived, independently of the type
of material used, gives the intelligibility rate (articulation score). This rate, even in normal persons, will
depend considerably on the test word material used, predominantly spondee words (already discussed under
whispered voice tests) and phonetically balanced words.
Annex 1, 6.3.4.1.1, Note 2, indicates that "in the speech material for discrimination testing, both
aviation-relevant phrases and phonetically balanced words are normally used". Tests should aim at an
assessment of strictly auditory functions and not depend on the ability to grasp the meaning of codes and
sentences heard incompletely, as in unfamiliar situations dangerous misunderstandings from incorrect
interpretation might occur. The following material is used in several States for testing speech intelligibility,
listed in order of increasing difficulty:
Short sentences: lists of simple sentences, subject, object and verb corresponding closely to normal
speech and R/T messages presented at various intensity levels. They might be supplemented by lists of
two-digit numbers. With normal hearing 100 per cent of this material is correctly understood.
Spondee words such as "aircraft, baseball, iceberg". The threshold is determined for a discrimination of
50 per cent.
Phonetically balanced (P-B) words: these are familiar monosyllabic (sometimes bisyllabic) words such
as "at, tree, by, ice" selected so as to approximate the distribution of sound in ordinary conversation.
The maximum P-B score is established at the individually optimal intensity level. Lists of phonetically
balanced words have been established for many languages.
Speech audiograms can be produced by varying the intensity levels at which the test material is presented
(abscissae) and plotting them against the speech intelligibility in percentages (ordinates). Separate curves may
be presented on the speech audiogram for spondees, P-B words, figures and short sentences as appropriate.
Although there appears to be a satisfactory degree of equivalence for the intelligibility of P-B lists in various
languages, better uniformity of testing procedures should be aimed at internationally, referring particularly to
the application of background noise (see Tables 12-4 and 12-5).
An applicant with normal hearing will hear and correctly repeat 95-100 per cent of these words at individually
suitable intensity levels. A discrimination score lower than 80 per cent should not be accepted. Those with
sensorineural loss may fail to achieve a satisfactory score. No matter how loud P-B words are presented, the
examinee with severe inner ear hearing loss fails to make an adequate score. In fact, if the intensity is increased
beyond the range of his most comfortable loudness, his score may even become worse. This is poor
discrimination ability.
In contrast, persons with conductive loss score high on this test. All that is required for them to hear well is
amplification. Thus, they can use hearing aids very satisfactorily.
ICAO Preliminary Unedited Version — October 2008 III-12-18
Certain frequencies are more important than others in the interpretation of speech. The most important
frequencies are 500, 1 000, 2 000 and 3 000 Hz. Speech is essentially compressed into this range, which is
sufficient for fairly complete understanding. In persons whose audiogram curves exhibit an abrupt drop, the
average of the best two frequencies may give better correlation. Discrimination is usually bad when the drop
affects speech frequencies. This is the person who will often remark, "I can hear you, but I can't understand
you." These individuals have difficulty in group conversation or when listening against a background of noise.
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Manual of Civil Aviation Medicine 2(82)
