noise exposure and auditory thresholds of german airline ...€¦ · germany fon: +49 641 9941316...
TRANSCRIPT
For peer review only
Noise exposure and auditory thresholds of civilian airline
pilots. A cross sectional study.
Journal: BMJ Open
Manuscript ID bmjopen-2016-012913
Article Type: Research
Date Submitted by the Author: 02-Jun-2016
Complete List of Authors: Müller, Reinhard; Universitätsklinikum Giessen und Marburg, Institut und Poliklinik für Arbeits- und Sozialmedizin Schneider, Joachim; Universitatsklinikum Giessen und Marburg Standort Giessen, Institut und Poliklinik für Arbeits- und Sozialmedizin
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Ear, nose and throat/otolaryngology
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, Audiology <
OTOLARYNGOLOGY, Noise and Health
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open on M
ay 2, 2020 by guest. Protected by copyright.
http://bmjopen.bm
j.com/
BM
J Open: first published as 10.1136/bm
jopen-2016-012913 on 30 May 2017. D
ownloaded from
For peer review only
Noise exposure and auditory thresholds of civilian airline pilots. A
cross sectional study.
Dr. Reinhard Müller and Prof. Dr. Joachim Schneider
Institut und Poliklinik für Arbeits- und Sozialmedizin am Universitätsklinikum
Giessen und Marburg.
1) Corresponding Author:
Dr. Reinhard Müller
IPAS Akustiklabor
Justus-Liebig-Universität Giessen
Aulweg 123
35392 Giessen
Germany
Fon: +49 641 9941316
Fax: +49 641 9941319
Mail: [email protected]
Keywords:
cockpit noise, hearing thresholds, influencing factors, left-right ear asymmetries, signal to
noise ratio
What this paper adds:
The cross sectional study in airline pilots shows significant worse hearing at the left ear.
The high sound levels of communication with headsets seem to be responsible for the
hearing loss.
Page 1 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
ABSTRACT
Objective: The cockpit workplace of airline pilots is a noisy environment. A sufficiently
good hearing is one of the fundamental conditions of this occupation.
Methods: 487 pilots of a German airline were analyzed due to their hearing thresholds
at 125 Hz – 16 kHz in two age groups under and over 40 years.
Results: The ambient noise levels in cockpits are between 74.0 dB(A) and 81.2 dB(A)
and the sound pressure levels for communication tasks under the headset between 85.5
dB(A) and 95.7 dB(A).
At all frequencies the older pilots have higher threshold levels (presbyacusis). The left-
right threshold differences at 3, 4 and 6 kHz show a clear effect of worse hearing at the
left ear increasing by age.
In the younger/older age group the mean differences at 3 kHz are 1.5/3.1 dB, at 4 kHz
1.5/3.6 dB and at 6 kHz 1.0/5.7 dB.
In the pilot group which used mostly the left ear for communication tasks (43 of 45 are
in the older age group) the mean difference at 3 kHz is 5.7 dB, at 4 kHz 7.0 dB and at 6
kHz 10.2 dB. The pilots who used the headset only at the right have also worse hearing
at the left ear of 2.3 dB at 3 kHz, 2.8 dB at 4 kHz and 2.6 dB at 6 kHz. The exposure
levels under the headset are about 19 dB(A) higher than outside. The signal to noise
ratio for communication tasks is averaged about 16 dB(A).
Conclusions: The left ear seems to be far more susceptible to noise induced hearing loss
than the right ear. The use of headsets with active noise reduction systems will reduce
the sound levels of communication under the upper exposure action value of 85 dB(A)
and allows a more relaxed way of working.
Strengths and limitations of this study
The current study is a large epidemiological study in civilian pilots over a wide age span
with acoustic measurements in various airplanes.
Hearing thresholds include extended high frequencies.
Multivariate analysis and differential presentation (left-right ear) identified unknown risk
factors influencing hearing thresholds.
A limitation is the cross-sectional design of the study.
Page 2 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
3
INTRODUCTION
Civilian airline pilots are an occupational group with high responsibility for life and limb of large
groups of people, where a wrong decision could lead to disastrous consequences for the entrusted
employees and passengers. The demands on the health and performance of pilots are correspondingly
high. Communication and the understanding of acoustic information are very important in their
occupation and a sufficiently good hearing is one of the fundamental conditions for the profession.
Therefore a hearing test at the annual health check-ups is mandatory. Nevertheless, there is still
discussion about the sound exposure for pilots and the consequences for their hearing. The present
study is a contribution to supplement existing publications and to uncover additional relationships at
crucial points. Presbyacusis is one main factor for decreasing of hearing ability through lifetime. It is
desirable to eliminate the factor age from the audiometric data to discover other factors like
occupational and environmental noise exposure of the pilots.
Page 3 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
4
STUDY POPULATION AND METHODS
Collective
Civilian pilots of a large German airline were examined during the annual health check-ups
with particular attention to their hearing status. All pilots were standardized interviewed
about their professional and leisure -related noise exposures. From a total of 542 candidates,
487 male pilots were included in the study. 12 pilots were excluded because their
questionnaires were imprecise. A further 12 people were excluded, because they did not
work in the cockpit and the 5 female pilots were excluded because the subgroup was too
small. Furthermore, 11 pilots were excluded due to sudden hearing loss, 12 due to former ear
surgery and 3 because of severe colds. So about 10 % of the examined subjects (55 out of
542) were not involved in the analysis. The mean age was 43 years (median: 38 years), with
a range from 20 (pilot candidates) to 63 years. Since a strong age dependency of the
audiograms was to be expected, the pilots were divided in two age groups. 271 pilots were
younger than 40 years old with 11 flight alumni, 209 first officers, 48 captains and 3 flight
engineers. 216 pilots were 40 years and older with 14 first officers, 180 captains and 25
flight engineers. The mean age of the younger group was 32.4 years and of the older group
48.8 years. The mean difference of age therefore was 16.4 years.
Instrumentation, Material
Pure tone audiometry was performed with an audiometer type CA540 from Hortmann
GmbH (now GN-Otometrics) and circum-aural headphones type HDA200 from Sennheiser
suitable for tests in the extended high frequency range up to 16 kHz. The maximum sound
levels of the CA540 in combination with the HDA200 are 90 dB HL at 11.2 kHz, 80 dB HL
at 12.5 kHz, 70 dB HL at 14 kHz and 60 dB HL at 16 kHz (HL: hearing level according to
ISO 389-5 and ISO 389-8)[1, 2]. Via the serial interface RS 232 the audiometric data were
recorded into a software database Avantgarde 2.0 of the company Nüß (Hamburg).
Acoustic Measurements
The acoustic measurements in aircraft cockpits were carried out by the technical service of
the aviation company. The measurements were performed with a ½ inch free-field
microphone and a dummy with an artificial middle ear Type 4157 of Brüel & Kjær
(Denmark). For all sound measurements an A-filter was used, as it meets the requirements.
The free-field microphone was placed at the side of the head near the ear of the pilot, the
dummy sat on a seat just behind the pilot and had a headset attached, in the same way as the
pilot. By using a middle ear simulator, frequencies above 250 Hz are considered stronger
rated than the pure A-rating.
Age-correction
Presbyacusis is the main influence factor in hearing thresholds if the study collective differs
widely in age. To analyze other factors it is useful to eliminate the factor age from the
dataset. The success of this procedure depends on the validity of the used age correction tool.
The ISO 7029 (2000)[3] is still valid but a new draft of ISO 7029 (2014) has new correction
Page 4 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
5
formulas leading to different results. The usage of age correction tables (examples of
database B) in ISO 1999 (2013) is also not helpful, because the three examples differ more
than the two versions of ISO 7029. The results and their interpretations depend on the
decision of witch version is used and become arbitrarily. Here we will demonstrate the
difference of both versions of ISO 7029 and renounce on the statistical analysis of age-
corrected threshold data. For further analysis differences between both ears were used with
the advantage to eliminate the aging effects on hearing thresholds.
Software and Statistics
All data were calculated with Excel 2013 in particular the age correction. Simple T-tests
were implemented in Excel to get hints for further evaluation. A comprehensive multi-
factorial ANOVA with repeated measures was calculated using SPSS 20.0 and shown in its
essential results as a table.
Page 5 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
6
RESULTS
Hearing Thresholds
The audiometric examinations of jet pilots from civil aviation companies were presented as
average audiograms. From 125 Hz to 8 kHz the octaves are presented equidistant with half
octaves from 500 Hz upwards. The last octave up to 16 kHz is spread by factor 1.5 with six
equidistant measure points. In fig. 1 the averaged thresholds of all pilots in the age groups
and both ears are presented in the upper part and the left-right differences in the lower part.
The results are two completely separated curves clearly indicating better hearing for younger
pilots as expected. At low frequencies up to 1.5 kHz the curves are parallel with differences
between 2 and 4 dB. From 2 kHz up to 14 kHz the differences increase up to about 30 dB.
The 16 kHz value in the older group is distorted by missing data caused by the limitations of
the audiometer. The lower part of Fig. 1 shows small threshold differences < ± 1 dB between
both ears up to 2 kHz. Here both curves cross the cero level from “right ear worse” to “left
ear worse” with increasing values. The curve of the younger pilots do not exceed levels over
± 2 dB. In the older pilots the threshold difference increases up to 6 dB worse hearing of the
left ear at 6 kHz. The 8 kHz value seems to be a local minimum in both age groups. In the
extended frequency range the differences between right and left ear decreased and approach
each other at 16 kHz at about 1 dB worse hearing of the left ear.
{fig.1}
Page 6 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
7
Tab. 1: Distribution of hearing levels averaged across left and right ears (dB HL) in four age-
groups.
In Tab. 1 the statistical distribution in the frequencies 3, 4 and 6 kHz is presented in four age-
groups with a span of ten years. 6 pilots are between 60 and 63 years old and not considered
in the distribution.
Page 7 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
8
Age-corrected thresholds
The effect of two different age corrections can be seen in fig. 2. The 2nd edition of ISO 7029
is presented in fig. 2a and the 3rd draft edition in fig. 2b. The frequency range is limited to
125 Hz up to 12.5 kHz the highest correction proposal in the 3rd draft edition. In fig. 2a the
correction of ISO 7029 (2000) is supplemented by correction values of Jilek et al. [4].
{fig. 2}
Altogether the new version of the ISO 7029 indicates a less influence of aging on hearing
thresholds, especially in the frequency range from 3 to 6 kHz where the influence of noise
(ISO 1999) is most pronounced. The threshold levels of the younger pilots differed only a
little (≤ 2 dB) while in the older pilots the thresholds increased to 3.5 dB at 4 kHz, 6 dB at 4
kHz, 5 dB at 6 kHz and 7 dB at 8 kHz. The better hearing in older pilots in fig. 2a shifts to a
worse hearing in fig. 2b by different age correcting factors according to ISO 7029.
Page 8 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
9
Cockpit Noise
For twelve jet models of a German airline, noise measurements were carried out in the
cockpit (Hoffmann 2004), which were supplemented by artificial head measurements. The
free-field measurements yielded values between 74.0 dB(A) for the A340 and 81.2 dB(A) for
B747-200 jets. The sound pressure levels for communication must be higher than the
ambient noise to be able to understand the messages. Therefore these levels had to be
measured (with an artificial head under the headset), to estimate effects on the hearing. In
Tab. 2 these measurement data are presented with measurement times. In contrast to the
uniformly ambient noise the communication signal fluctuates and contains impulsive parts of
noise. Therefore these measurements were captured with the time constant “impulse” (attack
time 35 ms, release time 1.5 sec.).
Tab. 2: Sound pressure level measurements in 12 different jet cockpits. Free-field
measurements are presented as well as measurements with an artificial head.
The mean difference between „fast“ and „impulse“ measurements with the artificial head is
5.4 dB and can be used as a correction factor in calculations of strongly fluctuating noise
effects on hearing. With the relative time period of air traffic control (ATC) to flight time
the real sound exposure of the pilots (Signal) during communication can be estimated. The
difference between “Signal” and the ambient noise (FF) is the signal to noise ratio for
communication. This value varies between minimal 8.6 dB in the Airbus 320 and a
maximum of 19.3 dB in the Boeing 757 on average about 15.7 dB.
The free field measured ambient noise in Airline cockpits do not reach the lower exposure
action values of 80 dB(A) of the EU directive 2003/10/EC[5] with one exception: the Boeing
B 747-200 has levels of 81.2 dB(A). The sound pressure levels of communication sound of
the air traffic control in all aircraft exceeds the upper exposure action value of the directive of
85 dB(A). The Airbus A320 has the lowest communication sound level with 85.5 dB(A). All
other aircraft exceed 90 dB(A) with a maximum of 95.7 dB(A) for the Airbus A 310-300.
Page 9 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
10
Statistics
With a multi-factorial ANOVA with repeated measures, the difference threshold data was
statistically evaluated for possible influencing factors (see Tab. 3). In addition to the age
group, four other dichotomous factors were selected, which suggests an impact on the
development of noise-induced hearing deteriorations as there are: acoustic shocks, military
service, attending discos, and the use of hearing protectors at noisy leisure activities. The
usage of the headset for communication has three options: right ear, left ear or both ears.
Tab. 3: Statistical analysis. ANOVA concerning threshold differences (left – right) with 6
grouping factors: age group, acoustic shocks, military service, disco visits, use of ear
protectors and use of the communication headset. A within group factor is the frequency.
Analyzed were 3, 4 and 6 kHz, which are predominantly affected by noise.
The factor age group shows significant increasing differences between both ears and the factor
headset ear shows a significant effect at p<0.001 on the worse hearing of the left ear.
The within-subjects factor contains the three frequencies 3, 4 and 6 kHz, which have the
strongest effect of noise according to ISO 1999 and is significant at p=0.02. Only 2-way
interactions between frequency and the other main factors were determined. With the exception
of “frequency x age” group all interactions are not significant and are not listed in Tab. 3.
Page 10 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
11
Headset
The dominant part of noise exposures results from communication sound as seen in Tab. 2.
More than half of the pilots (N=276) use the headset on both ears, while the others prefer to
use only one ear for radio communication resulting in a lower acoustic load of the ambient
noise at the other ear.
{fig. 3}
In Fig. 3 the effects of this different behavior on the threshold differences between the ears is
presented. Between pilots with the headset on both ears and the right ear the curves are close
together. Only at 4 kHz the difference exceeds 1 dB in the standard frequency range up to 8
kHz. The pilots who prefer to use the left ear for communication tasks, show a conspicuous
worse hearing at the left ear in the analyzed frequencies with more than 7 dB at 6 kHz. At 8
kHz the effect is noticeably smaller and increases in the extended high range between 9 and
11 kHz. The 12.5 kHz threshold difference is similar to 8 kHz less affected.
{fig. 4}
The preferred headset usage in the age groups is presented in Fig. 4. With 57 % more than
half of the pilots used both ears for radio communications. About a third (34 %) preferred to
use only the right ear and 9 % only the left ear. The pilots with left ear preference were all
captains sitting on the left seat with the right ear free for normal cockpit communication. 43
of this captains were older than 40 years and only 2 of them younger.
Page 11 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
12
DISCUSSION
As expected, the age of the pilots is the main influence factor on the hearing ability. Fig. 1a
shows a clear separation of the two age group curves. At frequencies above 2 kHz the age
dependent differences increase. The course at 14 and 16 kHz is affected by lack of
measurements in older pilots by the limited sound pressure level of the audiometer at these
frequencies. The threshold differences between left and right ear (Fig. 1b) show a clear
tendency to worse hearing of the left ear. This tendency is most pronounced at frequencies 3 –
6 kHz and 9 – 11 kHz in both age groups and much stronger in the older pilots. At lower
frequencies (< 3 kHz) the difference values oscillate round the cero line in a ± 1 dB range. At
1 kHz both age groups show better hearing by 1 dB of the left ear and no dependence on age.
Age adjustment in accordance with ISO 7029[3] should eliminate the age-related effects from
the data. The Fig. 2 shows the results of two versions of ISO 7029. The second edition from
2000 shows a stronger dependence of the age than the new draft edition from 2014. In the case
of our dataset we get reverse results in the interesting frequency range 3 – 6 kHz. Age corrected
with the second edition the older pilots hear better and a positive influence of the noise situation
would be concluded. With the third edition the younger pilots hear better and we recognize
noise induced hearing loss. While the third edition represents a draft and the second edition is
still valid we recognize the closer outcomes of our study with the new ISO 7029 version.
In Tab. 1 the distribution of threshold measurements are presented. Compared to the
screened dataset of Engdahl et al.[6] the percentiles of our data are by an average of 4.5 dB
lower and the 80 % span in the dataset is by an average of 9 dB smaller.
The free-field sound measurements in Tab. 2 (Hoffmann 2004) in aircraft cockpits show
sound pressure levels between 74.0 dB(A) and 81.2 dB(A). Lindgren et al[7] published lower
values between 71 dB(A) and 76 dB(A). Begault[8] described higher values between 75
dB(A) for the Airbus A 310 and 84 dB(A) for the Boeing B 727. The values of Hoffmann are
between this both measurement data sets. Non of the free field sound pressure levels of the
ambient noise reach the upper exposure action value of 85 dB(A).
In contrast, Gassaway[9] has identified significantly higher values in cockpits of propeller
aircraft from an average of 95 dB(A) and strongly recommended the use of hearing
protection. Military aircraft are usually even louder. Overall, these measurements are not
directly comparable, since the measured aircraft are not the same and certainly also vary in
the cockpit design and the measurement setup.
The noise exposure level caused by the radio communication exceeds the ambient cockpit
noise by far, because the messages have to be understood completely. In tests for speech
recognition mostly a 50 % criterion is used to determine the normal skill [10]. At sound
pressure levels of 83 dB SPL Killion et al. [11] found a word recognition score of 50 % at a
corresponding signal-to-noise ratio (SNR-50) of 7 dB. A word recognition score of 80 %
requires a SNR-80 of about 15 dB. The largely standardized communication in aviation has a
high redundancy in the transferred messages. Therefore, a score of near 100 % is achieved at
lower SNRs. In the current study the mean SNR used by the pilots was 15.7 dB, obviously
enough for a recognition rate of 100 %. In modern headsets for pilots active noise reduction
(ANR) systems are now commonly installed, which reduces masking low- frequency noise of
Page 12 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
13
the cockpit [12, 13]. The sound pressure level of the radio-communication can substantially
be reduced to a level below the lower exposure action value of 80 dB(A). In military pilots
another system seems to be more effective, the communications earplug. This is a small
sound transducer with ear plug function used under the standard flight helmet with good
results [14]. The pilots of the current study did not use any of these hearing protection
systems.
211 of the 487 pilots had a preference to use the communications headset mostly at only one
ear. This subgroup is suited to analyze the effect of radio communication on hearing. 166
pilots preferred the right ear, 45 pilots the left ear and 276 used both ears. Fig. 3 shows
significant differences between these groups. The differences between pilots who use both ears
and predominantly the right ear for communication are quite small (max. at 4 kHz 1.3 dB). The
left ear, however, shows significant greater differences with more than 7 dB at 6 kHz. In
Tab. 1 this fact can be seen in the strongest effect of the ANOVA for headset usage with
p < 0.001. With the exception of two pilots all of these pilots are in the older age group. This
asymmetry can be recognized in fig. 1 in the older age group to a lesser degree as in fig. 3
were the subgroup with left ear preference is particularly striking.
The right ear seems to be more resistant against the effects of noise than the left ear, because
the pilots with headset at the right ear almost do not differ significantly from those with
headset at both ears. Left-right ear threshold asymmetries are described by Pirilä et al. [15].
In the frequency range between 3 and 6 kHz these authors found higher thresholds at the left
ear and concluded a greater susceptibility to noise induced hearing loss of the left ear as a
biological effect. Influences like handedness and the audiometric test procedure with
learning and fatigue effects could be excluded [16, 17, 18]. This effect was also present in
females with smaller amount, because they are in general less exposed to noise. The pilot
group who used both ears for communication tasks show no increased damaging effect at the
left ear, although both ears had the same sound exposure level. A possible explanation of this
result could be the advantage of the binaural hearing [19] with the squelch-effect (summation
of interesting sound and unmasking of the noise) what leads to reduced communication
sound levels at a given ambient noise.
Based on the present findings, it can be concluded that the pilots of civil aviation have a good
hearing ability compared to other industrial workers with comparable noise exposure levels.
The left ear shows markedly higher risk of hearing damage than the right ear. If this effect is
age dependent cannot be answered with the current dataset. Modern headsets with noise
reduction function solve this problem and eliminate the risk for hearing loss in pilots.
Page 13 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
14
Acknowledgements
The authors thank Gerald Fleischer for his ideas and suggestions as well as the management
of data collection in the Lufthansa service center in Frankfurt/Main. Also thanks to Knut
Hoffmann of Lufthansa Technik in Hamburg for the measurement data in jet cockpits.
Conflict of interest declaration
The authors declare no conflict of interest.
Data sharing statement
No additional data available.
Funding statement
No funding.
Ethics statement
The audiometric measurements were carried out as part of the annual health checkups and
personal questions answered pilots voluntarily.
Contributorship statement
Conception and design: Reinhard Müller and Joachim Schneider
Administrative support: Reinhard Müller
Provision of study materials and patients: Reinhard Müller
Collection and assembly of data: Reinhard Müller
Data analysis and interpretation: Reinhard Müller and Joachim Schneider
Manuscript writing: Reinhard Müller and Joachim Schneider
Final approval of manuscript: Reinhard Müller and Joachim Schneider
Page 14 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
15
References
1. ISO 389-5. Acoustics – Reference zero for the calibration of audiometric equipment
– Part 5: Reference equivalent threshold sound pressure levels for pure tones in the
frequency range 8 kHz to 16 kHz. Geneva, Switzerland: International Organization
for Standardization. 1999.
2. ISO 389-8. Acoustics – Reference zero for the calibration of audiometric equipment –
Part 8: Reference equivalent threshold sound pressure levels for pure tones and circum-
aural earphones. Geneva, Switzerland: International Organization for Standardization.
2004.
3. ISO 7029. Acoustics – Statistical distribution of hearing thresholds as a function of age.
Geneva, Switzerland: International Organization for Standardization. 2000.
4. Jilek M, Suta D, Syka J. Reference hearing thresholds in an extended frequency
range as a function of age. J Acoust Soc Am. 2014;136(4):1821–1830.
5. EU DIRECTIVE 2003/10/EC OF THE EUROPEAN PARLIAMENT AND OF
THE COUNCIL (2007)
6. Engdahl B, Tambs K, Borchgrevink HM, Hoffman HJ. Screened and unscreened
hearing threshold levels for an adult population: Results from the Nord-Trøndelag
Hearing Loss Study. Int J Audiol. 2005; 44:213–230
7. Lindgren T, Wieslander G, Dammström BG, Norbäck D. Hearing status among
commercial pilots in a Swedish airline company. Int J Audiol. 2008;47:515–519
8. Begault DR, Wenzel EM. Assessment of noise exposure in commercial aircraft
cockpits (interim report). 1998; Available online at: http:/human-
factors.arcnasa.gov/publibary/Begault_1998_Noise_in_Cockpit.pdf.
9. Gasaway DC. Noise levels in cockpits of aircraft during normal cruise and
considerations of auditory risk. Aviat Space Environ Med. 1986;57: 103–112.
10. Thibodeau LM. Speech Audiometry. In Roeser JR, Valente M and Hosford-Dunn
H. Audiology. 2nd Ed. Thieme, 2007. New York, Stuttgart
11. Killion MC, Niquette PA, Gudmundsen GI. Development of a quick speech- in-noise
test for measuring signal-to-noise ratio loss in normal-hearing and hearing-impared
listeners. J Acoust Soc Am. 2004;116(4):2395–2405.
12. Matschke RG. Communication and noise Speech intelligibility of aircraft pilots with
and without electronic compensation for noise. HNO. 1994;42:499–504.
13. Casali JG. Powered Electronic Augmentations in Hearing Protection Technology Circa
2010 including Active Noise Reduction, Electronically-Modulated Sound Transmission,
and Tactical Communications Devices: Review of Design, Testing, and Research.
International Journal of Acoustics and Vibration. 2010;15(4): 168–186.
14. Casto KL, Casali JG. Effects of headset, flight workload, hearing ability, and
communications message quality on pilot performance. Human Factors. 2013;55(3):
486–498.
Page 15 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
16
15. Pirilä T, Jounio-Ervasti K, Sorri M. Left-right asymmetries in hearing threshold levels
in three age groups of a random population. Audiology 1992;31:150–161.
16. Pirilä T, Jounio-Ervasti K, Sorri M. Hearing asymmetry among left-handed and right-
handed persons in a random population. Scand. Audiol. 1991;20:223–226.
17. Axelsson A, Jerson T, Lindberg U, Lindgren F. Early noise-induced hearing loss in
teenaged boys. Scand. Audiol. 1981;10:91–96.
18. Borod J, Obner L, Albert M, Stiefel S. Lateralization for pure tone perception as a
function of age and sex. Cortex 1983;19:281–285.
19. Arsenault MD, Punch JL. Nonsense-syllable recognition in noise using monaural and
binaural listening strategies. J Acoust Soc Am. 1999;105(3):1821–1830.
Figures
Fig. 1: Hearing thresholds of civilian airline pilots in two age groups at both ears averaged (a)
from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 normal hearing levels
(dB HL). Part b shows the differences between left and right ear in dB.
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are
age corrected according to standard ISO 7029 in two editions: 2nd (upper part a) and 3
rd draft
(lower part b)
Fig. 3: Averaged threshold differences (left ear – right ear) according to the preferred
headset usage from 125 Hz up to 12.5 kHz.
Fig. 4: Age groups and preferred headset usage.
Page 16 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 1: Hearing thresholds of civilian airline pilots in two age groups at both ears averaged (a) from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 normal hearing levels (dB HL). Part b shows the
differences between left and right ear in dB.
Page 17 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are age corrected according to standard ISO 7029 in two editions: 2nd (upper part a) and 3rd draft (lower part b)
Page 18 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 3: Averaged threshold differences (left ear – right ear) according to the preferred headset usage from 125 Hz up to 12.5 kHz.
Page 19 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 4: Age groups and preferred headset usage.
Page 20 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Noise exposure and auditory thresholds of civilian airline
pilots. A cross sectional study. (Revised version)
Journal: BMJ Open
Manuscript ID bmjopen-2016-012913.R1
Article Type: Research
Date Submitted by the Author: 19-Sep-2016
Complete List of Authors: Müller, Reinhard; Universitätsklinikum Giessen und Marburg, Institut und Poliklinik für Arbeits- und Sozialmedizin Schneider, Joachim; Universitatsklinikum Giessen und Marburg Standort Giessen, Institut und Poliklinik für Arbeits- und Sozialmedizin
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Ear, nose and throat/otolaryngology
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, Audiology <
OTOLARYNGOLOGY, Noise and Health
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open on M
ay 2, 2020 by guest. Protected by copyright.
http://bmjopen.bm
j.com/
BM
J Open: first published as 10.1136/bm
jopen-2016-012913 on 30 May 2017. D
ownloaded from
For peer review only
Noise exposure and auditory thresholds of civilian airline pilots. A
cross sectional study. (Revised version)
Dr. Reinhard Müller and Prof. Dr. Joachim Schneider
Institut und Poliklinik für Arbeits- und Sozialmedizin am Universitätsklinikum
Giessen und Marburg.
1) Corresponding Author:
Dr. Reinhard Müller
IPAS Akustiklabor
Justus-Liebig-Universität Giessen
Aulweg 123
35392 Giessen
Germany
Fon: +49 641 9941316
Fax: +49 641 9941319
Mail: [email protected]
Keywords:
cockpit noise, hearing thresholds, influencing factors, left-right ear asymmetries, signal to
noise ratio
What this paper adds:
The cross sectional study in airline pilots shows significant worse hearing at the left ear.
High sound levels of communication with headsets seem to be responsible for the hearing
loss at the left ear which is more susceptible to hearing loss.
Page 1 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
ABSTRACT
Objective: The cockpit workplace of airline pilots is a noisy environment. The study
examines the hearing thresholds of pilots with respect of ambient noise and
communication sound.
Methods: The hearing of 487 German pilots was analyzed by audiometry in the
frequency range 125 Hz – 16 kHz in age-groups. Cockpit noise (free-field) and
communication sound (acoustic manikin) measurements were edited.
Results: The ambient noise levels in cockpits are between 74.0 dB(A) and 79.9 dB(A)
and the sound pressure levels under the headset between 83.5 dB(A) and 88.1 dB(A).
The left-right threshold differences at 3, 4 and 6 kHz show a clear effect of worse
hearing at the left ear increasing by age.
In the age-groups <40/≥40 years the mean differences at 3 kHz are 1.5/3.1 dB, at 4 kHz
1.5/3.6 dB and at 6 kHz 1.0/5.7 dB.
In the pilot group which used mostly the left ear for communication tasks (43 of 45 are in
the older age group) the mean difference at 3 kHz is 5.7 dB, at 4 kHz 7.0 dB and at 6 kHz
10.2 dB. The pilots who used the headset only at the right have also worse hearing at the
left ear of 2.3 dB at 3 kHz, 2.8 dB at 4 kHz and 2.6 dB at 6 kHz. The frequency corrected
exposure levels under the headset are between 7.0 and 11.4 dB(A) higher as the ambient
noise with a averaged signal to noise ratio for communication of about 10 dB(A).
Conclusions: The left ear is more susceptible than the right ear to hearing loss. Active
noise reduction systems reduce the sound levels of communication below the upper
exposure action value of 85 dB(A) and allow a more relaxed working for pilots.
Strengths and limitations of this study
The current study is a large epidemiological study in civilian pilots over a wide age span
with acoustic measurements in various airplanes.
Hearing thresholds include extended high frequencies.
Multivariate analysis and differential presentation (left-right ear) identified unknown risk
factors influencing hearing thresholds.
A limitation is the cross-sectional design of the study.
Page 2 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
3
INTRODUCTION
Civilian airline pilots are an occupational group with high responsibility for life and limb of
large groups of people, where a wrong decision could lead to disastrous consequences for the
entrusted employees and passengers. The demands on the health and performance of pilots
are correspondingly high. Communication and the understanding of acoustic information are
very important in their occupation and a sufficiently good hearing is one of the fundamental
conditions for the profession. Therefore a hearing test at the annual health check-ups is
mandatory. Nevertheless, there is still discussion about the sound exposure for pilots and the
consequences for their hearing.
Modern jet aircrafts are less noisy than former models what results in reduced annoyance of the
affected population. However, this will be overcompensated by raised flight amount. The
extend to which it affects the sound pressure levels in flight cabins and therefore the pilots and
passengers is another question. Lindgren et al. [1] for example did not find an extended risk to
hearing loss in Swedish airline pilots compared to a non-noise exposed population. The upper
action values of 85 dB(A) were generally not reached. They also found about 1.2 dB worse
thresholds in the left ear compared to the right ear. Lie et al. [2] reported in a review about
occupational noise exposure no articles with markedly increased risk to hearing impairment in
civilian airline pilots. However there are hints to an increased susceptibility to hearing loss of
the left ear compared to the right ear Pirilä et al. [3] and Cruickshanks et al. [4]. In studies to the
hearing of pilots the left-right ear asymmetries are considered only negligible. This subject will
be addressed in the present study.
Presbyacusis is one main factor for decreasing of hearing ability through lifetime. Therefore it
is desirable to eliminate the factor age from the audiometric data to discover other factors like
occupational and environmental noise exposure of the pilots by using existing standards to a
suitable age correction. The usefulness of age correction standards will be demonstrated in
the present paper.
Page 3 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
4
METHODS
Study Population
Civilian pilots of a large German airline were examined during the annual health check-ups
with particular attention to their hearing status. All pilots were interviewed in a standardized
manner about their professional and leisure -related noise exposures. From a total of 542
candidates, 487 male pilots were included in the study. 12 pilots were excluded because their
questionnaires were lost or incomplete. A further 12 people were excluded, because they did
not work in the cockpit and the 5 female pilots were excluded because the subgroup was too
small. Furthermore, 11 pilots were excluded due to sudden hearing loss, 12 due to former ear
surgery and 3 because of severe colds. So about 10 % of the examined subjects (55 out of
542) were not involved in the analysis. The mean age was 43 years (median: 38 years), with
a range from 20 (pilot candidates) to 63 years. Since a strong age dependency of the
audiograms was to be expected, the pilots were divided in two age groups. 271 pilots were
younger than 40 years old with 11 flight alumni, 209 flight officers, 48 captains and 3 flight
engineers. 216 pilots were 40 years and older with 14 flight officers, 180 captains and 25
flight engineers. The mean age of the younger group was 32.4 years and of the older group
48.8 years. The mean difference of age therefore was 16.4 years. Four age groups with ten
year range were pooled for statistical characteristics (percentiles).
Instrumentation, Material
Pure tone audiometry was performed by experienced audiologist’s assistants in a sound proof
room of the medical center of the airline company. The audiometer was type CA540 from
Hortmann GmbH (now GN-Otometrics) with circum-aural headphones type HDA200 from
Sennheiser suitable for tests in the extended high frequency range up to 16 kHz. The
maximum sound levels of the CA540 in combination with the HDA200 are 90 dB HL at
11.2 kHz, 80 dB HL at 12.5 kHz, 70 dB HL at 14 kHz and 60 dB HL at 16 kHz (HL:
hearing level according to ISO 389-5 and ISO 389-8)[5, 6]. Via the serial interface RS 232
the audiometric data were recorded into a software database Avantgarde 2.0 of the company
Nüß (Hamburg).
Acoustic Measurements
The acoustic measurements in aircraft cockpits were carried out by the technical service of
the aviation company. The measurements were performed with a ½ inch free-field
microphone and an acoustic manikin Type 4100 with an artificial middle ear Type 4157 of
Brüel & Kjær (Denmark). In all sound measurements integrating function and an A-filter was
used, as it corresponds to the regulations in the EU DIRECTIVE 2003/10/EC [7]. The free-
field microphone was placed besides the pilot near the ear. The acoustic manikin was placed
on a seat just behind the pilot wearing a headset in the same way as the pilot receiving the
same signal. The headset was a two-sided supra-aural headphone without active noise
attenuation. The middle ear simulator conforms to IEC 60318-4, ANSI 3.25 and ITU-T Rec.
P.47. The frequency response and impedance is similar to the real human ear.
Page 4 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
5
Age-correction
Presbyacusis is the main influence factor in hearing thresholds if the study collective differs
widely in age. To analyze other factors it is useful to eliminate the factor age from the
dataset. The success of this procedure depends on the validity of the used age correction tool.
The ISO 7029 (2000)[8] is still valid but a new draft of ISO 7029 (2014) has new correction
formulas leading to different results. The usage of age correction tables (examples of
database B) in ISO 1999 (2013) [9] is also not helpful, because the three examples differ
more than the two versions of ISO 7029 [8]. The results and their interpretations depend on
the decision of which version is used and become arbitrarily. In the current study we will
demonstrate the difference of both versions of ISO 7029 [8] and renounce on the statistical
analysis of age-corrected threshold data. The focus of the paper was placed on individual
left-right threshold differences because they do not require age-correction.
Software and Statistics
All data were calculated with Excel 2013 in particular the age correction. Simple T-tests
were implemented in Excel to get hints for further evaluation. A comprehensive multi-
factorial ANOVA with repeated measures was calculated using SPSS 20.
Page 5 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
6
RESULTS
Hearing Thresholds
The audiometric examinations of jet pilots from a German airline company were presented as
average audiograms in age-groups both ears together and the averaged differences between
both ears. In Fig. 1a the averaged thresholds of all pilots in the age groups and both ears are
presented in the upper part and the left-right differences in the lower part Fig 1b. The results
are two completely separated curves clearly indicating better hearing for younger pilots. At
low frequencies up to 1.5 kHz the curves are parallel with differences between 2 and 4 dB.
From 2 kHz up to 14 kHz the differences increase up to about 30 dB. The 16 kHz value in
the older group is distorted by missing data caused by the limitations of the audiometer.
Fig. 1b shows small threshold differences < ± 1 dB between both ears up to 2 kHz. Here both
curves cross the zero level from “right ear worse” to “left ear worse” with increasing values.
The curve of the younger pilots does not exceed levels over ± 2 dB. In the older pilots the
threshold difference increases up to 6 dB worse hearing of the left ear at 6 kHz. The 8 kHz
value seems to be a local minimum in both age groups. In the extended frequency range the
differences between right and left ear decreased and approach each other at 16 kHz at about
1 dB worse hearing of the left ear.
{Fig. 1}
Tab. 1: Distribution of hearing levels averaged across left and right ears (dB HL) in four age-
groups.
Frequency Centile Age (years)
20–29 30–39 40–49 50–59
3 kHz 10 -5.0 -2.5 0.0 2.5
25 0.0 0.0 2.5 7.5
Median 0.0 2.5 7.5 11.3
75 5.0 5.0 12.5 17.5
90 10.0 10.0 20 25.8
3 kHz 10 0.0 0.0 3.3 7.5
25 0.0 2.5 7.5 12.5
Median 5.0 5.0 12.5 17.5
75 10.0 10.0 19.4 26.9
90 17.5 15.0 27.5 35.0
3 kHz 10 0.0 0.0 5.0 7.5
25 5.0 5.0 10.0 12.5
Median 10.0 7.5 13.8 21.3
75 15.0 12.5 22.5 29.4
90 20.0 17.5 35.0 37.5
N 74 197 133 77
In Tab. 1 the statistical distribution in the frequencies 3, 4 and 6 kHz is presented in four age-groups
with a span of ten years. 6 pilots are between 60 and 63 years old and not considered in the
distribution.
Page 6 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
7
Age-corrected thresholds
The effect of two different age corrections can be seen in Fig. 2. The 2nd edition of ISO 7029
[8] is presented in Fig. 2a and the 3rd draft edition in Fig. 2b. The frequency range is limited
to 125 Hz up to 12.5 kHz the highest correction proposal in the 3rd draft edition.
{Fig. 2}
Altogether the new version of the ISO 7029 indicates a smaller influence of aging on hearing
thresholds, especially in the frequency range from 3 to 6 kHz where the influence of noise
(ISO 1999) is most pronounced. The threshold levels of the younger pilots differed only a
little (≤ 2 dB) while in the older pilots the thresholds increased to 3.5 dB at 4 kHz, 6 dB at 4
kHz, 5 dB at 6 kHz and 7 dB at 8 kHz. The better hearing in older pilots in Fig. 2a shifts to a
worse hearing in Fig. 2b by different age correcting factors according to ISO 7029 [8].
Page 7 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
8
Cockpit Noise and Communication Sound
For nine jet models of a German airline, free field noise measurements were carried out in
the cockpit (Hoffmann 2004) [10], which were supplemented by acoustic manikin
measurements. The free-field measurements yielded values between 74 dB(A) for the B767
and 80 dB(A) for B747 jets. The sound pressure levels for communication are higher than
the ambient noise for a clear understanding of the messages. These sound pressure levels
were measured with an acoustic manikin under the headset to estimate effects on hearing. In
Tab. 2 these measurement data are presented with measurement times and the time portion
with communication (ATC) in minutes. In contrast to the uniformly ambient noise the
communication signal fluctuates and contains impulsive parts of sound. Therefore the
measurements with time constant “fast” (125 ms) were supplemented by measurements with
the time constant “impulse” (attack time 35 ms, release time 1.5 sec.).
Tab. 2: Sound pressure level measurements in 9 different jet cockpits. Free field ambient
noise (AN) measurement data during flight time are presented as well as data from an acoustic
manikin (AM). Measurement data from Hoffmann [10]. AMcATC are calculated values by
using the ISO 11904-2 [11] and the ATC time.
Jet Data Sound Pressure Data
Type Flight time ATC time ANFt AMfFt AMiFt AMcATC SNR
minutes minutes dB(A)f dB(A)f dB(A)i dB(A)f dB(A)
A310-200 162 70 74.9 81.9 87.9 83.5 8.6
A310-300 460 208 76.7 86.7 92.7 88.1 11.4
B737-200 221 81 76.8 81.4 87.4 83.8 7.0
B737-300 137 28 77.3 80.9 85.9 85.8 8.5
B747 1144 344 79.9 84.8 89.9 88.0 8.1
B757 357 134 75.1 83.7 89.9 86.0 10.9
B767 294 112 74.4 81.6 87.9 83.8 9.4
DC10 116 50 76.8 85.9 91.2 87.6 10.8
MD11 153 73 75.0 84.6 90.3 85.8 10.8
ATC(air trafic control), Ft(Flight time), AN(free field ambient noise), AM(acoustic manikin), SNR(signal to noise ratio)
dB(A)f(sound pressure level with A-weighting and time constant: fast), dB(A)i(with time constant: impulse)
AMcATC (spectral corrected values of AMfFt by ISO 11904-2 and calculated to the ATC time).
The differences between „impulse“and „fast“ measurements with the acoustic manikin
(AMiFt – AMfFt) are between 5 and 6 dB and can be used as a correction factor for
impulsive noise and its special effects on hearing (not listed in Tab. 2). With the time period
of air traffic control (ATC) compared to the total flight time the equivalent sound exposure
of the pilots during communication can be estimated after a spectral correction according to
ISO 11904-2 [11]. This was done in the column AMcATC. The difference between AMcATC
and the ambient noise (ANFt) is the signal to noise ratio (SNR) for communication. This
value varies between minimal 7 dB and maximal 11 dB. The average is about 10 dB.
The free field measured ambient noise in Airline cockpits does not reach the lower exposure
action values of 80 dB(A) of the EU DIRECTIVE 2003/10/EC [7]. The corrected sound
pressure levels of communication sound (ATC) exceeds in 6 cases the upper exposure action
Page 8 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
9
value of the directive of 85 dB(A). The minimum communication sound level was calculated
to 83.5 dB(A) in the Airbus A320-200, and the maximum level to 88.1 dB(A) in the Airbus
A310-300.
Statistics
With a multi-factorial ANOVA with repeated measures, the difference threshold data was
statistically evaluated for possible influencing factors (see Tab. 3). In addition to the age
group, four other dichotomous factors were selected, which suggests an impact on the
development of noise-induced hearing deteriorations as there are: acoustic shocks, military
service, attending discos, and the use of hearing protectors at noisy leisure activities. The
usage of the headset for communication has three options: right ear, left ear or both ears.
Tab. 3: Statistical analysis. ANOVA concerning threshold differences (left – right) with 6
grouping factors: age group, acoustic shocks, military service, disco visits, use of ear
protectors and use of the communication headset. A within group factor is the frequency.
Analyzed were 3, 4 and 6 kHz, which are predominantly affected by noise.
between groups df F p
AgeGrp 1 8.711 0.003
AcousticShock 1 1.838 0.160
Military 1 0.142 0.707
Disco 1 0.672 0.413
EarProt 1 1.654 0.199
HeadsetEar 2 8.685 <0.001
within groups
Frequency 2 5.473 0.020
Frequency * AgeGrp 2 6.111 0.014
Significant factors and interactions (*) are expressed bold
The factor age group shows significant increasing differences between both ears and the factor
headset ear shows a significant effect at p<0.001 on the worse hearing of the left ear.
The within-subjects factor contains the three frequencies 3, 4 and 6 kHz, which have the
strongest effect of noise according to ISO 1999 [9] and is significant at p=0.02. Only 2-way
interactions between frequency and the other main factors were determined. With the exception
of “frequency x age group” all interactions are not significant and are not listed in Tab. 3.
Headset
The dominant part of noise exposures results from communication sound as seen in Tab. 2.
More than half of the pilots (N=276) use the headset on both ears, while the others prefer to
use only one ear for radio communication.
{Fig. 3}
The preferred headset usage in the age groups is presented in Fig. 3. More than half of the
pilots (57 %) used both ears for radio communications. About a third (34 %) preferred to use
Page 9 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
10
only the right ear and 9 % only the left ear. The pilots with left ear preference were all
captains sitting on the left seat with the right ear free for normal cockpit communication. 43
of these captains were older than 40 years and only 2 of them younger.
{Fig. 4}
In Fig. 4 the effects of this different behavior on the threshold differences between the ears is
presented. Between pilots with the headset on both ears and the right ear the curves are close
together. Only at 4 kHz the difference exceeds 1 dB in the standard frequency range up to 8
kHz. The pilots who prefer to use the left ear for communication tasks, show a conspicuous
worse hearing at the left ear in the analyzed frequencies with more than 7 dB at 6 kHz. At 8
kHz the effect is noticeably smaller and increases in the extended high range between 9 and
11 kHz. The 12.5 kHz threshold difference is similar to 8 kHz less affected.
Page 10 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
11
DISCUSSION
As expected, the age of the pilots is the main influence factor on the hearing ability. Fig. 1a
shows a clear separation of the two age group curves. At frequencies above 2 kHz the age
dependent differences increase. The course at 14 and 16 kHz is affected by lack of
measurements in older pilots by the limited sound pressure level of the audiometer at these
frequencies. The threshold differences between left and right ear (Fig. 1b) show a clear
tendency to worse hearing of the left ear. This tendency is most pronounced at frequencies 3 –
6 kHz and 9 – 11 kHz in both age groups and much stronger in the older pilots. At lower
frequencies (< 3 kHz) the difference values oscillate around the zero line within a ± 1 dB
range. At 1 kHz both age groups show better hearing by 1 dB of the left ear and no
dependence on age.
Age adjustment in accordance with ISO 7029 [8] should eliminate the age-related effects
from the data. The Fig. 2 shows the results of two versions of ISO 7029 [8]. The second edition
in Fig. 2a from 2000 shows a stronger dependence of the age than the new draft edition in
Fig. 2b from 2014. In the case of our dataset we get reverse results in the interesting frequency
range 3 – 6 kHz. Age corrected with the second edition the older pilots hear better and a
positive influence of the noise situation would be concluded. With the third edition the younger
pilots hear better and we recognize hearing loss. While the third edition represents a draft and
the second edition is still valid we recognize the closer outcomes of our study with the new
ISO 7029 [8] version.
In Tab. 1 the distribution of threshold measurements are presented. Compared to the
screened dataset of Engdahl et al.[12] the percentiles of our data are lower on an average of
4.5 dB and the 80 % span in our dataset is smaller on an average of 9 dB.
The free-field sound data of Hoffmann [10] in Tab. 2 in aircraft cockpits show sound
pressure levels between 74 dB(A) and 80 dB(A). Lindgren et al[1] published lower values
between 71 dB(A) and 76 dB(A). Begault [13] described higher values between 75 dB(A) for
the Airbus A 310 and 84 dB(A) for the Boeing B 727. The ambient noise in cockpits reported
by Lower and Bagshaw [14] had levels between 71 and 79 dB(A). The values of Hoffmann
[10] are in between this measurement data sets from literature. None of the free field sound
pressure levels of the ambient noise reach the upper exposure action value of 85 dB(A). If we
take into account, that noise with impulsive character is more harmful than pure continuous
noise, for noise exposure levels by communication the impulse correction factor should be
added. Here this factor is between 5 and 6 dB and do this we reach in all cases the upper
exposure action values but only during communication. As the ACT time is mostly shorter
than half of the total flight time and never 8 hours, the impulse correction factor will be
compensated approximately by the shorter exposure time. The equivalent exposure levels of
our pilots are than around the upper exposure action value of 85 dB(A) in 8 hours.
Gassaway[15] has identified significantly higher values in cockpits of propeller aircraft from
an average of 95 dB(A) and strongly recommended the use of hearing protection. Military
aircraft are usually even louder. Overall, these measurements are not directly comparable,
since the measured aircraft are not the same and certainly also vary in the cockpit design and
the measurement setup.
Page 11 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
12
The noise exposure level caused by the radio communication exceeds the ambient cockpit
noise, because the messages have to be understood completely. In tests for speech in noise
recognition mostly a 50 % criterion is used to determine the normal skill [16]. At sound
pressure levels of 83 dB SPL Killion et al. [17] found a word recognition score of 50 % at a
corresponding signal-to-noise ratio (SNR-50) of about 2 dB. Pilots need full understanding of
the messages corresponding to SNR-100 at much higher SNR values. The largely standardized
communication in aviation has a high redundancy in the transferred messages. Therefore, a
score of near 100 % is achieved at lower SNRs as the SNR-100. In the current study the
average SNR used by the pilots was at 10 dB, obviously enough for a recognition rate of
100 %. Lower and Bagshaw [14] measured communication spectral corrected sound levels
between 80 and 88 dB(A). Compared with the corresponding ambient noise levels a SNR
between 6 and 13 dB(A) can be calculated with an average of about 10 dB(A) like in our
dataset.
Circum-aural headsets with passive sound attenuation can be helpful to reduce the
communication sound levels, but they impede the communication between the crew as the
attenuation at high frequencies is much better than at low frequencies in that earphones.
Headsets with active noise reduction (ANR) systems are now commonly installed, which
reduces predominantly masking low- frequency noise of the cockpit [18, 19]. The sound
pressure level of the radio-communication can substantially be reduced to a level below the
lower exposure action value of 80 dB(A). The pilots of the current study did not use any
hearing protection systems. The protective effect depends on wearing the headset at both
ears. Open headsets with low frequency noise reduction may allow communication between
captain and flight officer as the masking effects are reduced.
211 of the 487 pilots had a preference to use the communications headset mostly at only one
ear. This subgroup is suited to analyze the effect of radio communication on hearing. 166
pilots preferred the right ear, 45 pilots the left ear and 276 used both ears. Fig. 4 shows
significant differences between these groups. The differences between pilots who use both ears
and predominantly the right ear for communication are quite small (max. at 4 kHz 1.3 dB). The
left ear, however, shows significant greater differences with more than 7 dB at 6 kHz. In
Tab. 1 this fact can be seen in the strongest effect of the ANOVA for headset usage with
p < 0.001. With the exception of two pilots all of these pilots are in the older age group. This
asymmetry can be recognized in Fig. 1b in the older age group to a lesser degree as in Fig. 4
were the subgroup with left ear preference is particularly striking.
The right ear seems to be more resistant against the effects of noise than the left ear, because
the pilots with headset at the right ear almost do not differ significantly from those with
headset at both ears. Left-right ear threshold asymmetries are described by Pirilä et al. [3]. In
the frequency range between 3 and 6 kHz these authors found higher thresholds at the left
ear and concluded a greater susceptibility to noise induced hearing loss of the left ear as a
biological effect. Influences like handedness and the audiometric test procedure with
learning and fatigue effects could be excluded [20, 21, 22]. This effect was also present in
females with smaller amount, because they are in general less exposed to noise. The higher
left-right differences in Cruickshanks et al. [4] may result from not exclude the shooters from
their dataset.
Page 12 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
13
The pilot group who used both ears for communication tasks show no increased damaging
effect at the left ear, although both ears had the same sound exposure level. A possible
explanation of this result could be the advantage of the binaural hearing [23] with the
squelch-effect (summation of interesting sound and unmasking of the noise) what leads to
reduced communication sound levels at a given ambient noise.
Based on the present findings, it can be concluded that the pilots of civil aviation have a good
hearing ability compared to other industrial workers with comparable noise exposure levels.
The left ear shows markedly higher risk of hearing damage than the right ear. If this effect is
age dependent cannot be answered with the current dataset. The use of headsets with active or
passive noise reduction at both ears can solve this last problem and may eliminate any risk for
hearing loss in pilots during their normal occupational activity. The hint to pilots to allways
use both ears for communication and never use only the left ear may also be helpful.
Page 13 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
14
Acknowledgements
The authors thank Gerald Fleischer for his ideas and suggestions as well as the management
of data collection in the Lufthansa service center in Frankfurt/Main. Also many thanks to
Knut Hoffmann of Lufthansa Technik in Hamburg for the measurement data in jet cockpits.
Conflict of interest declaration
The authors declare no conflict of interest.
Data sharing statement
No additional data available.
Funding statement
No funding.
Ethics statement
The audiometric measurements were carried out as part of the annual health checkups and
personal questions answered pilots voluntarily with consent to publish the data anonymously.
Contributorship statement
Conception and design: Reinhard Müller and Joachim Schneider
Administrative support: Reinhard Müller
Provision of study materials and patients: Reinhard Müller
Collection and assembly of data: Reinhard Müller
Data analysis and interpretation: Reinhard Müller and Joachim Schneider
Manuscript writing: Reinhard Müller and Joachim Schneider
Final approval of manuscript: Reinhard Müller and Joachim Schneider
Page 14 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
15
References
1. Lindgren T, Wieslander G, Dammström BG, Norbäck D. Hearing status among
commercial pilots in a Swedish airline company. Int J Audiol. 2008;47:515–519
2. Lie A, Skogstad M, Johannessen HA, Tynes T, Mehlum IS, Nordby KC, Engdahl B
and Tambs K. Occupational noise exposure and hearing: a systematic review. Int Arch
Occup Environ Health 2016; 89:351–372.
3. Pirilä T, Jounio-Ervasti K, Sorri M. Left-right asymmetries in hearing threshold levels
in three age groups of a random population. Audiology 1992;31:150–161.
4. Cruickshanks KJ, Wiley TL, Tweed TS, Klein BEK, Klein R, Mares-Perlman JA and
Nondahl DM. Prevalence of hearing loss in older adults in Beaver Dam, Wisconsin:
the epidemiology of hearing loss study. Am J Epidemiol. 1998;148(9):879–886.
5. ISO 389-5. Acoustics – Reference zero for the calibration of audiometric equipment
– Part 5: Reference equivalent threshold sound pressure levels for pure tones in the
frequency range 8 kHz to 16 kHz. Geneva, Switzerland: International Organization
for Standardization. 1999.
6. ISO 389-8. Acoustics – Reference zero for the calibration of audiometric equipment –
Part 8: Reference equivalent threshold sound pressure levels for pure tones and circum-
aural earphones. Geneva, Switzerland: International Organization for Standardization.
2004.
7. EU DIRECTIVE 2003/10/EC OF THE EUROPEAN PARLIAMENT AND OF
THE COUNCIL (2007)
8. ISO 7029. Acoustics – Statistical distribution of hearing thresholds as a function of age.
Geneva, Switzerland: International Organization for Standardization. 2000.
9. ISO 1999. Acoustics – Estimation of noise induced hearing loss. Geneva, Switzerland:
International Organization for Standardization. 2013.
10. Hoffmann K. Sound measurements in cockpits of civilian aircraft. 2004. Not poblished
data received as personal communication.
11. ISO 11904-2. Acoustics – Determination of sound immissions from sound sources
placed close to the ears – Part 2: Technique using a manikin. Geneva, Switzerland:
International Organization for Standardization. 2004.
12. Engdahl B, Tambs K, Borchgrevink HM, Hoffman HJ. Screened and unscreened
hearing threshold levels for an adult population: Results from the Nord-Trøndelag
Hearing Loss Study. Int J Audiol. 2005; 44:213–230
13. Begault DR, Wenzel EM. Assessment of noise exposure in commercial aircraft
cockpits (interim report). 1998; Available online at: http:/human-
factors.arcnasa.gov/publibary/Begault_1998_Noise_in_Cockpit.pdf.
14. Lower MC, Bagshaw M. Noise levels and communication on the flight decks of civil
aircraft. 25th Internoise proc. 1996.
Page 15 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
16
15. Gasaway DC. Noise levels in cockpits of aircraft during normal cruise and
considerations of auditory risk. Aviat Space Environ Med. 1986;57: 103–112.
16. Thibodeau LM. Speech Audiometry. In Roeser JR, Valente M and Hosford-Dunn
H. Audiology. 2nd Ed. Thieme, 2007. New York, Stuttgart
17. Killion MC, Niquette PA, Gudmundsen GI. Development of a quick speech- in-noise
test for measuring signal-to-noise ratio loss in normal-hearing and hearing-impared
listeners. J Acoust Soc Am. 2004;116(4):2395–2405.
18. Matschke RG. Communication and noise Speech intelligibility of aircraft pilots with
and without electronic compensation for noise. HNO. 1994;42:499–504.
19. Casali JG. Powered Electronic Augmentations in Hearing Protection Technology Circa
2010 including Active Noise Reduction, Electronically-Modulated Sound Transmission,
and Tactical Communications Devices: Review of Design, Testing, and Research.
International Journal of Acoustics and Vibration. 2010;15(4): 168–186.
20. Pirilä T, Jounio-Ervasti K, Sorri M. Hearing asymmetry among left-handed and right-
handed persons in a random population. Scand. Audiol. 1991;20:223–226.
21. Axelsson A, Jerson T, Lindberg U, Lindgren F. Early noise-induced hearing loss in
teenaged boys. Scand. Audiol. 1981;10:91–96.
22. Borod J, Obner L, Albert M, Stiefel S. Lateralization for pure tone perception as a
function of age and sex. Cortex 1983;19:281–285.
23. Arsenault MD, Punch JL. Nonsense-syllable recognition in noise using monaural and
binaural listening strategies. J Acoust Soc Am. 1999;105(3):1821–1830.
Figures
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears
averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal
hearing levels (dB HL). Part b shows the differences between left and right ear in dB.
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are
age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3
rd
draft (lower part b)
Fig. 3: Age groups and preferred headset usage.
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred
headset usage from 125 Hz up to 12.5 kHz.
Page 16 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal hearing levels (dB HL). Part b
shows the differences between left and right ear in dB.
Page 17 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3rd draft (lower part b)
Page 18 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 3: Age groups and preferred headset usage.
Page 19 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred headset usage from 125 Hz up to 12.5 kHz.
130x72mm (300 x 300 DPI)
Page 20 of 20
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Noise exposure and auditory thresholds of German airline
pilots. A cross sectional study.
Journal: BMJ Open
Manuscript ID bmjopen-2016-012913.R2
Article Type: Research
Date Submitted by the Author: 22-Nov-2016
Complete List of Authors: Müller, Reinhard; Universitätsklinikum Giessen und Marburg, Institut und Poliklinik für Arbeits- und Sozialmedizin Schneider, Joachim; Universitatsklinikum Giessen und Marburg Standort Giessen, Institut und Poliklinik für Arbeits- und Sozialmedizin
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Ear, nose and throat/otolaryngology
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, Audiology <
OTOLARYNGOLOGY, Noise and Health
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open on M
ay 2, 2020 by guest. Protected by copyright.
http://bmjopen.bm
j.com/
BM
J Open: first published as 10.1136/bm
jopen-2016-012913 on 30 May 2017. D
ownloaded from
For peer review only
Noise exposure and auditory thresholds of German airline pilots.
A cross sectional study.
Dr. Reinhard Müller1 and Prof. Dr. Joachim Schneider
2
1,2) Institut und Poliklinik für Arbeits- und Sozialmedizin am Universitätsklinikum
Giessen und Marburg.
1) Corresponding Author:
Dr. Reinhard Müller
IPAS Akustiklabor
Justus-Liebig-Universität Giessen
Aulweg 123
35392 Giessen
Germany
Fon: +49 641 9941316
Fax: +49 641 9941319
Mail: [email protected]
Keywords:
cockpit noise, hearing thresholds, influencing factors, left-right ear asymmetries, signal to
noise ratio
What this paper adds:
The cross sectional study in airline pilots shows that a pilots sense of hearing is likely to be
significantly more impaired on the left ear. The cause of this is probably their exposure to
high sound levels of communication with headsets to which the left is more susceptible to
damage.
Page 1 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
ABSTRACT
Objective: The cockpit workplace of airline pilots is a noisy environment. This study
examines the hearing thresholds of pilots with respect to ambient noise and
communication sound.
Methods: The hearing of 487 German pilots was analyzed by audiometry in the
frequency range of 125 Hz – 16 kHz in varying age-groups. Cockpit noise (free-field)
data and communication sound (acoustic manikin) measurements were evaluated.
Results: The ambient noise levels in cockpits were found to be between 74 dB(A) and
80 dB(A) and the sound pressure levels under the headset were found to be between 84
dB(A) and 88 dB(A).
The left-right threshold differences at 3, 4 and 6 kHz show evidence of impaired hearing
at the left ear, which worsens by age.
In the age-groups <40/≥40 years the mean differences at 3 kHz are 2/3 dB, at 4 kHz
2/4 dB and at 6 kHz 1/6 dB.
In the pilot group which used mostly the left ear for communication tasks (43 of 45 are in
the older age group) the mean difference at 3 kHz is 6 dB, at 4 kHz 7 dB and at 6 kHz
10 dB. The pilots who used the headset only at the right ear also show worse hearing at
the left ear of 2 dB at 3 kHz, 3 dB at 4 kHz and at 6 kHz. The frequency corrected
exposure levels under the headset are between 7 and 11 dB(A) higher than the ambient
noise with a averaged signal to noise ratio for communication of about 10 dB(A).
Conclusions: The left ear is more susceptible than the right ear to hearing loss. Active
noise reduction systems allow for a reduced sound level for the communication signal
below the upper exposure action value of 85 dB(A) and allow for a more relaxed
working environment for pilots.
Strengths and limitations of this study
The current study is a large epidemiological study in civilian pilots over a wide age span
with acoustic measurements in various airplanes.
Hearing thresholds include extended high frequencies.
Multivariate analysis and differential presentation (left-right ear) identified unknown risk
factors influencing hearing thresholds.
A limitation is the cross-sectional design of the study.
Page 2 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
3
INTRODUCTION
Civilian airline pilots bear a high responsibility as one wrong decision could lead to
disastrous consequences for the entrusted employees and passengers. The demands on the
health and performance of pilots are correspondingly high. Communication and the
understanding of acoustic information are very important in their occupation and a
sufficiently good hearing is one of the fundamental conditions for the profession. Therefore a
hearing test at the annual health check-ups is mandatory. Nevertheless, sound exposure for
pilots and the consequences for their hearing is still being discussed.
Modern jet aircrafts are less noisy than former models. This results in reduced noise exposure in
the flight cabin and less annoyance for the affected population. However, the reduced
annoyance per flight will be overcompensated by a higher flight frequency. Lindgren et al. [1]
for example did not find an extended risk to hearing loss in Swedish airline pilots compared to a
non-noise exposed population. The upper action values of 85 dB(A) were generally not
reached. They also found about 1.2 dB worse thresholds in the left ear when compared to the
right ear. Lie et al. [2] reported in a review about occupational noise exposure no articles with
markedly increased risk to hearing impairment in civilian airline pilots. However there are hints
about an increased susceptibility to hearing loss of the left ear compared to the right, which are
independent of the occupation [3, 4]. In studies to the hearing of pilots the left-right ear
asymmetries are considered only negligible. This subject will be addressed in the present study.
Presbyacusis is one main factor for a decreasing hearing ability over age. Therefore it is
desirable to eliminate the age factor from the audiometric data so as to discover other factors
like occupational and environmental noise exposure of the pilots. This can be done by using
existing standards to a suitable age correction. The usefulness of age correction standards
will be demonstrated in the present paper.
Page 3 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
4
METHODS
Study Population
Civilian pilots of a large German airline were examined during the annual health check-ups
with particular attention to their hearing status. All pilots were interviewed in a standardized
manner about their professional and leisure -related noise exposures. From a total of 542
candidates, 487 male pilots were included in the study. 12 pilots were excluded because their
questionnaires were lost or incomplete. Further 12 people were excluded, because they did
not work in the cockpit and the 5 female pilots were excluded because the subgroup was too
small. Furthermore, 11 pilots were excluded due to sudden hearing loss, 12 due to former ear
surgery and 3 because of severe colds. So about 10 % of the examined subjects (55 out of
542) were not involved in the analysis. The mean age was 43 years (median: 38 years), with
a range from 20 (pilot candidates) to 63 years. Since a strong age dependency of the
audiograms was to be expected, the pilots were divided in two age groups. 271 pilots were
younger than 40 years old with 11 flight alumni, 209 flight officers, 48 captains and 3 flight
engineers. 216 pilots were 40 years and older with 14 flight officers, 180 captains and 25
flight engineers. The mean age of the younger group was 32.4 years and of the older group
48.8 years. The mean difference of age therefore was 16.4 years. Four age groups with ten
year range were pooled for statistical characteristics (percentiles).
Instrumentation, Material
Pure tone audiometry was performed by experienced audiologist’s assistants in a sound proof
room of the medical center of the airline company. The audiometer was a type CA540 from
Hortmann GmbH (now GN-Otometrics) with circum-aural headphones type HDA200 from
Sennheiser suitable for tests in the extended high frequency range up to 16 kHz. The
maximum sound levels of the CA540 in combination with the HDA200 are 90 dB HL at
11.2 kHz, 80 dB HL at 12.5 kHz, 70 dB HL at 14 kHz and 60 dB HL at 16 kHz (HL:
hearing level according to ISO 389-5 and ISO 389-8)[5, 6]. Via the serial interface RS 232
the audiometric data were recorded into a software database Avantgarde 2.0 of the company
Nüß (Hamburg).
Acoustic Measurements
The acoustic measurements in aircraft cockpits were carried out by the technical service of
the aviation company. The measurements were performed with a ½ inch free-field
microphone and an acoustic manikin Type 4100 with an artificial middle ear Type 4157 of
Brüel & Kjær (Denmark). In all sound measurements integrating function and an A-filter
were used, as it corresponds to the regulations in the EU DIRECTIVE 2003/10/EC [7]. The
free-field microphone was placed beside the pilot near the ear. The acoustic manikin was
placed on a seat just behind the pilot wearing a headset in the same way as the pilot receiving
the same signal. The headset was a two-sided supra-aural headphone without active noise
attenuation. The middle ear simulator conforms to IEC 60318-4, ANSI 3.25 and ITU-T Rec.
P.47. The frequency response and impedance is similar to the real human ear.
Page 4 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
5
Age-correction
Presbyacusis is the main influence factor in hearing thresholds if the study collective differs
widely in age. To analyze other factors it is advisable to eliminate the age factor from the
dataset. The success of this procedure depends on the validity of the used age correction tool.
The ISO 7029 (2000)[8] is still valid but a new draft of ISO 7029 (2014) has new correction
formulas leading to different results. The usage of age correction tables (examples of
database B) in ISO 1999 (2013) [9] is also not helpful, because the three examples differ
more than the two versions of ISO 7029 [8]. The results and their interpretations depend on
the decision of which version is used and become arbitrary. In the current study we will
demonstrate the difference of both versions of ISO 7029 [8] and renounce on the statistical
analysis of age-corrected threshold data. The focus of the paper was placed on individual
left-right threshold differences because they do not require age-correction.
Software and Statistics
All data were calculated with Excel 2013 in particular the age correction. Simple T-tests
were implemented in Excel to get hints for further evaluation. A comprehensive multi-
factorial ANOVA with repeated measures was calculated using SPSS 20.
Page 5 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
6
RESULTS
Hearing Thresholds
The audiometric examinations of jet pilots from a German airline company are presented as
average audiograms in age-groups, hereby evaluating both ears and the averaged differences
between both ears. In Fig. 1a the averaged thresholds of all pilots in the age groups and both
ears are presented in the upper part and the left-right differences in the lower part Fig 1b. The
results are two completely separated curves clearly indicating better hearing for younger
pilots. At low frequencies up to 1.5 kHz the curves are parallel with differences between 2
and 4 dB. From 2 kHz up to 14 kHz the differences increase up to about 30 dB. The 16 kHz
value in the older group is distorted by missing data caused by the limitations of the
audiometer. Fig. 1b shows small threshold differences < ± 1 dB between both ears up to 2
kHz. Here both curves cross the zero level from “right ear worse” to “left ear worse” with
increasing values. The curve of the younger pilots does not exceed levels over ± 2 dB. In the
older pilots the threshold difference increases up to 6 dB at 6 kHz. The 8 kHz value seems to
be a local minimum in both age groups. In the extended frequency range the differences
between right and left ear decreases and approach each other at 16 kHz at about 1 dB.
{Fig. 1}
Tab. 1: Distribution of hearing levels averaged across left and right ears (dB HL) in four age-
groups.
Frequency Centile Age (years)
20–29 30–39 40–49 50–59
3 kHz 10 -5.0 -2.5 0.0 2.5
25 0.0 0.0 2.5 7.5
Median 0.0 2.5 7.5 11.3
75 5.0 5.0 12.5 17.5
90 10.0 10.0 20 25.8
4 kHz 10 0.0 0.0 3.3 7.5
25 0.0 2.5 7.5 12.5
Median 5.0 5.0 12.5 17.5
75 10.0 10.0 19.4 26.9
90 17.5 15.0 27.5 35.0
6 kHz 10 0.0 0.0 5.0 7.5
25 5.0 5.0 10.0 12.5
Median 10.0 7.5 13.8 21.3
75 15.0 12.5 22.5 29.4
90 20.0 17.5 35.0 37.5
N 74 197 133 77
In Tab. 1 the statistical distribution in the frequencies 3, 4 and 6 kHz is presented in four age-groups
with a span of ten years. 6 pilots are between 60 and 63 years old and not considered in the
distribution.
Page 6 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
7
Age-corrected thresholds
The effect of two different age corrections can be seen in Fig. 2. The 2nd edition of ISO 7029
[8] is presented in Fig. 2a and the 3rd draft edition in Fig. 2b. Frequency range is limited to
125 Hz up to 12.5 kHz the highest correction proposal in the 3rd draft edition.
{Fig. 2}
Altogether the new version of the ISO 7029 indicates a smaller influence of aging on hearing
thresholds, especially in the frequency range from 3 to 6 kHz where the influence of noise
(ISO 1999) is most pronounced. The threshold levels of the younger pilots differed only a
little (≤ 2 dB) while in the older pilots the thresholds increased to 3.5 dB at 4 kHz, 6 dB at 4
kHz, 5 dB at 6 kHz and 7 dB at 8 kHz. The better hearing in older pilots in Fig. 2a shifts to a
worse hearing in Fig. 2b by different age correcting factors according to ISO 7029 [8].
Page 7 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
8
Cockpit Noise and Communication Sound
For nine jet models of a German airline, free field noise measurements were carried out in
the cockpit (Hoffmann 2004) [10], which were supplemented by acoustic manikin
measurements. The free-field measurements yielded values between 74 dB(A) for the B767
and 80 dB(A) for B747 jets. The sound pressure levels for communication are higher than
the ambient noise for a clear understanding of the messages. These sound pressure levels
were measured with an acoustic manikin under the headset to estimate effects on hearing. In
Tab. 2 these measurement data are presented with measurement times and the time portion
with communication (ATC) in minutes. In contrast to the uniformly ambient noise the
communication signal fluctuates and contains impulsive parts of sound. Therefore the
measurements with time constant “fast” (125 ms) were supplemented by measurements with
the time constant “impulse” (attack time 35 ms, release time 1.5 sec.).
Tab. 2: Sound pressure level measurements in 9 different jet cockpits. Free field ambient
noise (AN) measurement data during flight time are presented as well as data from an acoustic
manikin (AM). Measurement data from Hoffmann [10]. AMcATC are calculated values by
using the ISO 11904-2 [11] and the ATC time.
Jet Data Sound Pressure Data
Type Flight time ATC time ANFt AMfFt AMiFt AMcATC SNR
minutes minutes dB(A)f dB(A)f dB(A)i dB(A)f dB(A)
A310-200 162 70 74.9 81.9 87.9 83.5 8.6
A310-300 460 208 76.7 86.7 92.7 88.1 11.4
B737-200 221 81 76.8 81.4 87.4 83.8 7.0
B737-300 137 28 77.3 80.9 85.9 85.8 8.5
B747 1144 344 79.9 84.8 89.9 88.0 8.1
B757 357 134 75.1 83.7 89.9 86.0 10.9
B767 294 112 74.4 81.6 87.9 83.8 9.4
DC10 116 50 76.8 85.9 91.2 87.6 10.8
MD11 153 73 75.0 84.6 90.3 85.8 10.8
ATC(air trafic control), Ft(Flight time), AN(free field ambient noise), AM(acoustic manikin), SNR(signal to noise ratio)
dB(A)f(sound pressure level with A-weighting and time constant: fast), dB(A)i(with time constant: impulse)
AMcATC (spectral corrected values of AMfFt by ISO 11904-2 and calculated to the ATC time).
The differences between „impulse“and „fast“ measurements with the acoustic manikin
(AMiFt – AMfFt) are between 5 and 6 dB and can be used as a correction factor for
impulsive noise and its special effects on hearing (not listed in Tab. 2). With the time period
of air traffic control (ATC) compared to the total flight time the equivalent sound exposure
of the pilots during communication can be estimated after a spectral correction according to
ISO 11904-2 [11]. This was done in the column AMcATC. The difference between AMcATC
and the ambient noise (ANFt) is the signal to noise ratio (SNR) for communication. This
value varies between minimal 7 dB and maximal 11 dB. The average is about 10 dB.
The free field measured ambient noise in Airline cockpits does not reach the lower exposure
action values of 80 dB(A) of the EU DIRECTIVE 2003/10/EC [7] if the flight time is below
8 hours. The corrected sound pressure levels of communication sound AMc(ATC) exceeds the
Page 8 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
9
upper exposure action value of the directive of 85 dB(A) in 6 cases for a flight times of 8
hours and more. The minimum communication sound level was calculated to 83.5 dB(A) in
the Airbus A320-200, and the maximum level to 88.1 dB(A) in the Airbus A310-300. Only
in intercontinental flights the flight time reaches or exceeds 8 hours.
Statistics
With a multi-factorial ANOVA with repeated measures, the left-right differences in the
threshold data were statistically evaluated for possible influencing factors (see Tab. 3). In
addition to the age group, four other dichotomous factors were selected, which suggests an
impact on the development of noise-induced hearing deteriorations as there are: acoustic
shocks, military service, attending discos, and the use of hearing protectors at noisy leisure
activities. The usage of the headset for communication has three options: right ear, left ear or
both ears.
Tab. 3: Statistical analysis. ANOVA concerning threshold differences (left – right) with 6
between groups factors: age group, acoustic shocks, military service, disco visits, use of ear
protectors and use of the communication headset. One within groups factor is the frequency.
Analyzed were 3, 4 and 6 kHz, which are predominantly affected by noise.
between groups df F p
AgeGrp 1 8.711 0.003
AcousticShock 1 1.838 0.160
Military 1 0.142 0.707
Disco 1 0.672 0.413
EarProt 1 1.654 0.199
HeadsetEar 2 8.685 <0.001
within groups
Frequency 2 5.473 0.020
Frequency * AgeGrp 2 6.111 0.014
Significant factors and interactions (*) are expressed bold
The factor age group shows significant increasing differences between both ears and the factor
headset ear shows a significant effect (p<0.001) on the worse hearing of the left ear.
The within-subjects factor contains the three frequencies 3, 4 and 6 kHz, which have the
strongest effect of noise according to ISO 1999 [9] and is significant at p=0.02. Only 2-way
interactions between frequency and the other main factors were determined. With the exception
of “frequency x age group” all interactions are not significant and are not listed in Tab. 3.
Page 9 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
10
Headset
The dominant part of noise exposures results from communication sound as seen in Tab. 2.
More than half of the pilots (N=276) use the headset on both ears, while the others prefer to
use only one ear for radio communication.
{Fig. 3}
The preferred headset usage in the age groups is presented in Fig. 3. More than half of the
pilots (57 %) used both ears for radio communications. About a third (34 %) preferred to use
only the right ear and 9 % only the left ear. The pilots with left ear preference were all
captains sitting on the left seat with the right ear free for normal cockpit communication. 43
of these captains were older than 40 years and only 2 of them younger.
{Fig. 4}
In Fig. 4 the effects of this different behavior on the threshold differences between the ears is
presented. Between pilots with the headset on both ears and the right ear the curves are close
together. Only at 4 kHz the difference exceeds 1 dB in the standard frequency range up to 8
kHz. The pilots who prefer to use the left ear for communication tasks, show a conspicuous
worse hearing at the left ear in the analyzed frequencies with more than 7 dB at 6 kHz. At 8
kHz the effect is noticeably smaller and increases in the extended high range between 9 and
11 kHz. The 12.5 kHz threshold difference decreases to a value of about 3 dB.
Page 10 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
11
DISCUSSION
As expected, the age of the pilots is the main influence factor on the hearing ability. Fig. 1a
shows a clear separation of the two age group curves. At frequencies above 2 kHz the age
dependent differences increase. The course at 14 and 16 kHz is affected by lack of
measurements in older pilots by the limited sound pressure level of the audiometer at these
frequencies. The threshold differences between left and right ear (Fig. 1b) show a clear
tendency to worse hearing of the left ear. This tendency is most pronounced at frequencies 3 –
6 kHz and 9 – 11 kHz in both age groups and much stronger in the older pilots. At lower
frequencies (< 3 kHz) the difference values oscillate around the zero line within a ± 1 dB
range. At 1 kHz both age groups show better hearing by 1 dB of the left ear and no
dependence on age.
Age adjustment in accordance with ISO 7029 [8] should eliminate the age-related effects
from the data. The Fig. 2 shows the results of two versions of ISO 7029 [8]. The second edition
in Fig. 2a from 2000 shows a stronger dependence of the age than the new draft edition in
Fig. 2b from 2014. In the case of our dataset we get reverse results in the interesting frequency
range 3 – 6 kHz. Age corrected with the second edition the older pilots hear better and a
positive influence of the noise situation would be concluded. With the third edition the younger
pilots hear better and we recognize hearing loss. While the third edition represents a draft and
the second edition is still valid we recognize the closer outcomes of our study with the new
ISO 7029 [8] version.
In Tab. 1 the distribution of threshold measurements are presented. Compared to the
screened dataset of Engdahl et al.[12] the percentiles of our data are lower on an average of
4.5 dB and the 80 % span in our dataset is smaller on an average of 9 dB.
The free-field sound data of Hoffmann [10] in Tab. 2 in aircraft cockpits show sound
pressure levels between 74 dB(A) and 80 dB(A). Lindgren et al[1] published lower values
between 71 dB(A) and 76 dB(A). Begault [13] described higher values between 75 dB(A) for
the Airbus A 310 and 84 dB(A) for the Boeing B 727. The ambient noise in cockpits reported
by Lower and Bagshaw [14] had levels between 71 and 79 dB(A). The values of Hoffmann
[10] are in between this measurement data sets from literature. None of the free field sound
pressure levels of the ambient noise reach the upper exposure action value of 85 dB(A). If we
take into account, that noise with impulsive character is more harmful than pure continuous
noise, for noise exposure levels by communication the “impulse correction factor” should be
added. Here this factor is between 5 and 6 dB and do this we reach in all cases the upper
exposure action values but only during communication. As the ACT time is mostly shorter
than half of the total flight time and never 8 hours, the “impulse correction factor” will be
compensated approximately by the shorter exposure time. The equivalent exposure levels of
our pilots are than around the upper exposure action value of 85 dB(A) in 8 hours.
Gassaway[15] has identified significantly higher values in cockpits of propeller aircraft from
an average of 95 dB(A) and strongly recommended the use of hearing protection. Military
aircraft are usually even louder. Overall, these measurements are not directly comparable,
since the measured aircraft are not the same and certainly also vary in the cockpit design and
the measurement setup.
Page 11 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
12
The noise exposure level caused by the radio communication exceeds the ambient cockpit
noise, because the messages have to be understood completely. In tests for speech-in-noise
recognition mostly a 50 % criterion is used to determine the normal skill [16]. At sound
pressure levels of 83 dB SPL Killion et al. [17] found a word recognition score of 50 % at a
corresponding signal-to-noise ratio of about 2 dB. Pilots need full understanding of the
messages at much higher SNR values. The largely standardized communication in aviation
has a high redundancy in the transferred messages, what reduces the required SNRs. In the
current study the average SNR used by the pilots was at 10 dB, obviously enough for a
recognition rate of about 100 %. Lower and Bagshaw [14] measured spectral corrected sound
levels for communication between 80 and 88 dB(A). Compared with the corresponding
ambient noise levels SNR values between 6 and 13 dB(A) can be calculated with an average
of about 10 dB(A) like in our dataset.
Circum-aural headsets with passive sound attenuation can be helpful to reduce the
communication sound levels, but they impede the communication between the crew as the
attenuation at high frequencies is much better than at low frequencies in those earphones.
Headsets with active noise reduction (ANR) systems are now commonly installed, which
reduces predominantly the masking low- frequency noise of the cockpit [18, 19]. The sound
pressure level of the radio-communication can substantially be reduced to a level below the
lower exposure action value of 80 dB(A). The pilots of the current study did not use any
hearing protection systems. The protective effect depends on wearing the headset on both
ears. Open headsets with low frequency noise reduction may allow communication between
captain and flight officer as the masking effects are reduced.
211 of the 487 pilots had a preference to use the communications headset mostly on only one
ear. This subgroup is suited to analyze the effect of radio communication on hearing. 166
pilots preferred the right ear, 45 pilots the left ear and 276 used both ears. Fig. 4 shows
significant differences between these groups. The differences between pilots who use both ears
and predominantly the right ear for communication are quite small (max. at 4 kHz 1.3 dB). The
left ear, however, shows significant greater differences with more than 7 dB at 6 kHz. In
Tab. 1 this fact can be seen as the strongest effect of the ANOVA for headset usage with
p < 0.001. With the exception of two pilots all of these pilots are in the older age group. This
asymmetry can be recognized in Fig. 1b in the older age group to a lesser degree as in Fig. 4
where the subgroup with left ear preference is particularly striking.
The right ear seems to be more resistant against the effects of noise than the left ear, because
the pilots with headset at the right ear almost do not differ significantly from those with
headset at both ears. Left-right ear threshold asymmetries are described by Pirilä et al. [3]. In
the frequency range between 3 and 6 kHz these authors found higher thresholds on the left
ear and concluded a greater susceptibility to noise induced hearing loss of the left ear as a
biological effect. Influences like handedness and the audiometric test procedure with
learning and fatigue effects could be excluded [20, 21, 22]. This effect was also present in
females to a lesser degree, because they are in general less exposed to noise. The higher left-
right differences in Cruickshanks et al. [4] may result from not excluding the users of
firearms from their dataset.
The pilot group who used both ears for communication tasks show no increased damaging
Page 12 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
13
effect at the left ear, although both ears had the same sound exposure level. A possible
explanation of this result could be the advantage of the binaural hearing [23] with the
squelch-effect (summation of interesting sound and unmasking of the noise) what leads to
reduced communication sound levels at a given ambient noise.
Based on the present findings, it can be concluded that the pilots of civil aviation have a good
hearing ability compared to other industrial workers with comparable noise exposure levels.
The left ear shows markedly higher risk of hearing damage than the right ear. If this effect is
age dependent cannot be answered with the current dataset. The use of headsets with active or
passive noise reduction at both ears can solve this last problem and may eliminate any risk for
hearing loss in pilots during their normal occupational activity. The hint to pilots to allways
use both ears for communication and never use only the left ear may also be helpful.
Page 13 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
14
Acknowledgements
The authors thank Gerald Fleischer for his ideas and suggestions as well as the management
of data collection in the Lufthansa service center in Frankfurt/Main. Also many thanks to
Knut Hoffmann of Lufthansa Technik in Hamburg for the measurement data in jet cockpits.
Conflict of interest declaration
The authors declare no conflict of interest.
Data sharing statement
No additional data available.
Funding statement
No funding.
Ethics statement
The audiometric measurements were carried out as part of the annual health checkups and
personal questions answered pilots voluntarily with consent to publish the data anonymously.
Contributorship statement
Conception and design: Reinhard Müller and Joachim Schneider
Administrative support: Reinhard Müller
Provision of study materials and patients: Reinhard Müller
Collection and assembly of data: Reinhard Müller
Data analysis and interpretation: Reinhard Müller and Joachim Schneider
Manuscript writing: Reinhard Müller and Joachim Schneider
Final approval of manuscript: Reinhard Müller and Joachim Schneider
Page 14 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
15
References
1. Lindgren T, Wieslander G, Dammström BG, Norbäck D. Hearing status among
commercial pilots in a Swedish airline company. Int J Audiol. 2008;47:515–519
2. Lie A, Skogstad M, Johannessen HA, Tynes T, Mehlum IS, Nordby KC, Engdahl B
and Tambs K. Occupational noise exposure and hearing: a systematic review. Int Arch
Occup Environ Health 2016; 89:351–372.
3. Pirilä T, Jounio-Ervasti K, Sorri M. Left-right asymmetries in hearing threshold levels
in three age groups of a random population. Audiology 1992;31:150–161.
4. Cruickshanks KJ, Wiley TL, Tweed TS, Klein BEK, Klein R, Mares-Perlman JA and
Nondahl DM. Prevalence of hearing loss in older adults in Beaver Dam, Wisconsin:
the epidemiology of hearing loss study. Am J Epidemiol. 1998;148(9):879–886.
5. ISO 389-5. Acoustics – Reference zero for the calibration of audiometric equipment
– Part 5: Reference equivalent threshold sound pressure levels for pure tones in the
frequency range 8 kHz to 16 kHz. Geneva, Switzerland: International Organization
for Standardization. 1999.
6. ISO 389-8. Acoustics – Reference zero for the calibration of audiometric equipment –
Part 8: Reference equivalent threshold sound pressure levels for pure tones and circum-
aural earphones. Geneva, Switzerland: International Organization for Standardization.
2004.
7. EU DIRECTIVE 2003/10/EC OF THE EUROPEAN PARLIAMENT AND OF
THE COUNCIL (2007)
8. ISO 7029. Acoustics – Statistical distribution of hearing thresholds as a function of age.
Geneva, Switzerland: International Organization for Standardization. 2000.
9. ISO 1999. Acoustics – Estimation of noise induced hearing loss. Geneva, Switzerland:
International Organization for Standardization. 2013.
10. Hoffmann K. Sound measurements in cockpits of civilian aircraft. 2004. Not poblished
data received as personal communication.
11. ISO 11904-2. Acoustics – Determination of sound immissions from sound sources
placed close to the ears – Part 2: Technique using a manikin. Geneva, Switzerland:
International Organization for Standardization. 2004.
12. Engdahl B, Tambs K, Borchgrevink HM, Hoffman HJ. Screened and unscreened
hearing threshold levels for an adult population: Results from the Nord-Trøndelag
Hearing Loss Study. Int J Audiol. 2005; 44:213–230
13. Begault DR, Wenzel EM. Assessment of noise exposure in commercial aircraft
cockpits (interim report). 1998; Available online at: http:/human-
factors.arcnasa.gov/publibary/Begault_1998_Noise_in_Cockpit.pdf.
14. Lower MC, Bagshaw M. Noise levels and communication on the flight decks of civil
aircraft. 25th Internoise proc. 1996.
Page 15 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
16
15. Gasaway DC. Noise levels in cockpits of aircraft during normal cruise and
considerations of auditory risk. Aviat Space Environ Med. 1986;57: 103–112.
16. Thibodeau LM. Speech Audiometry. In Roeser JR, Valente M and Hosford-Dunn
H. Audiology. 2nd Ed. Thieme, 2007. New York, Stuttgart
17. Killion MC, Niquette PA, Gudmundsen GI. Development of a quick speech- in-noise
test for measuring signal-to-noise ratio loss in normal-hearing and hearing-impared
listeners. J Acoust Soc Am. 2004;116(4):2395–2405.
18. Matschke RG. Communication and noise Speech intelligibility of aircraft pilots with
and without electronic compensation for noise. HNO. 1994;42:499–504.
19. Casali JG. Powered Electronic Augmentations in Hearing Protection Technology Circa
2010 including Active Noise Reduction, Electronically-Modulated Sound Transmission,
and Tactical Communications Devices: Review of Design, Testing, and Research.
International Journal of Acoustics and Vibration. 2010;15(4): 168–186.
20. Pirilä T, Jounio-Ervasti K, Sorri M. Hearing asymmetry among left-handed and right-
handed persons in a random population. Scand. Audiol. 1991;20:223–226.
21. Axelsson A, Jerson T, Lindberg U, Lindgren F. Early noise-induced hearing loss in
teenaged boys. Scand. Audiol. 1981;10:91–96.
22. Borod J, Obner L, Albert M, Stiefel S. Lateralization for pure tone perception as a
function of age and sex. Cortex 1983;19:281–285.
23. Arsenault MD, Punch JL. Nonsense-syllable recognition in noise using monaural and
binaural listening strategies. J Acoust Soc Am. 1999;105(3):1821–1830.
Figures
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears
averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal
hearing levels (dB HL). Part b shows the differences between left and right ear in dB.
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are
age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3
rd
draft (lower part b)
Fig. 3: Age groups and preferred headset usage.
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred
headset usage from 125 Hz up to 12.5 kHz.
Page 16 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal hearing levels (dB HL). Part b
shows the differences between left and right ear in dB.
Page 17 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3rd draft (lower part b)
Page 18 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 3: Age groups and preferred headset usage.
Page 19 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred headset usage from 125 Hz up to 12.5 kHz.
130x72mm (300 x 300 DPI)
Page 20 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
1
Statement—Checklist
Item
No Recommendation
On
Page
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 1
(b) Provide in the abstract an informative and balanced summary of what was done
and what was found
2
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 3
Objectives 3 State specific objectives, including any prespecified hypotheses 3
Methods
Study design 4 Present key elements of study design early in the paper 4
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,
exposure, follow-up, and data collection
4
Participants 6 (a) Give the eligibility criteria, and the sources and methods of selection of
participants
4
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect
modifiers. Give diagnostic criteria, if applicable
-
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of
assessment (measurement). Describe comparability of assessment methods if there
is more than one group
-
Bias 9 Describe any efforts to address potential sources of bias -
Study size 10 Explain how the study size was arrived at 4
Quantitative
variables
11 Explain how quantitative variables were handled in the analyses. If applicable,
describe which groupings were chosen and why
-
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 5
(b) Describe any methods used to examine subgroups and interactions 9
(c) Explain how missing data were addressed -
(d) If applicable, describe analytical methods taking account of sampling strategy -
(e) Describe any sensitivity analyses -
Results
Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially
eligible, examined for eligibility, confirmed eligible, included in the study,
completing follow-up, and analysed
4, 10
(b) Give reasons for non-participation at each stage 4
(c) Consider use of a flow diagram -
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and
information on exposures and potential confounders
-
(b) Indicate number of participants with missing data for each variable of interest -
Outcome data 15* Report numbers of outcome events or summary measures -
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and
their precision (eg, 95% confidence interval). Make clear which confounders
were adjusted for and why they were included
-
(b) Report category boundaries when continuous variables were categorized -
(c) If relevant, consider translating estimates of relative risk into absolute risk for a
meaningful time period
-
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and
sensitivity analyses
-
Page 21 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
Discussion
Key results 18 Summarise key results with reference to study objectives
Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or
imprecision. Discuss both direction and magnitude of any potential bias
11
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,
multiplicity of analyses, results from similar studies, and other relevant evidence
12
Generalisability 21 Discuss the generalisability (external validity) of the study results 13
Other information
Funding 22 Give the source of funding and the role of the funders for the present study and, if
applicable, for the original study on which the present article is based
-
*Give information separately for exposed and unexposed groups.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published
examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the
Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and
Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
Page 22 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Noise exposure and auditory thresholds of German airline
pilots. A cross sectional study.
Journal: BMJ Open
Manuscript ID bmjopen-2016-012913.R3
Article Type: Research
Date Submitted by the Author: 25-Jan-2017
Complete List of Authors: Müller, Reinhard; Universitätsklinikum Giessen und Marburg, Institut und Poliklinik für Arbeits- und Sozialmedizin Schneider, Joachim; Universitatsklinikum Giessen und Marburg Standort Giessen, Institut und Poliklinik für Arbeits- und Sozialmedizin
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Ear, nose and throat/otolaryngology
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, Audiology <
OTOLARYNGOLOGY, Noise and Health
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open on M
ay 2, 2020 by guest. Protected by copyright.
http://bmjopen.bm
j.com/
BM
J Open: first published as 10.1136/bm
jopen-2016-012913 on 30 May 2017. D
ownloaded from
For peer review only
Noise exposure and auditory thresholds of German airline pilots.
A cross sectional study.
Dr. Reinhard Müller1 and Prof. Dr. Joachim Schneider
2
1,2) Institut und Poliklinik für Arbeits- und Sozialmedizin am Universitätsklinikum
Giessen und Marburg.
1) Corresponding Author:
Dr. Reinhard Müller
IPAS Akustiklabor
Justus-Liebig-Universität Giessen
Aulweg 123
35392 Giessen
Germany
Fon: +49 641 9941316
Fax: +49 641 9941319
Mail: [email protected]
Keywords:
cockpit noise, hearing thresholds, influencing factors, left-right ear asymmetries, signal to
noise ratio
What this paper adds:
The cross sectional study in airline pilots shows that a pilots sense of hearing is likely to be
significantly more impaired on the left ear. The cause of this is probably their exposure to
high sound levels of communication with headsets to which the left is more susceptible to
damage.
Page 1 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
ABSTRACT
Objective: The cockpit workplace of airline pilots is a noisy environment. This study
examines the hearing thresholds of pilots with respect to ambient noise and
communication sound.
Methods: The hearing of 487 German pilots was analyzed by audiometry in the
frequency range of 125 Hz – 16 kHz in varying age-groups. Cockpit noise (free-field)
data and communication sound (acoustic manikin) measurements were evaluated.
Results: The ambient noise levels in cockpits were found to be between 74 dB(A) and
80 dB(A) and the sound pressure levels under the headset were found to be between 84
dB(A) and 88 dB(A).
The left-right threshold differences at 3, 4 and 6 kHz show evidence of impaired hearing
at the left ear, which worsens by age.
In the age-groups <40/≥40 years the mean differences at 3 kHz are 2/3 dB, at 4 kHz
2/4 dB and at 6 kHz 1/6 dB.
In the pilot group which used mostly the left ear for communication tasks (43 of 45 are in
the older age group) the mean difference at 3 kHz is 6 dB, at 4 kHz 7 dB and at 6 kHz
10 dB. The pilots who used the headset only at the right ear also show worse hearing at
the left ear of 2 dB at 3 kHz, 3 dB at 4 kHz and at 6 kHz. The frequency corrected
exposure levels under the headset are between 7 and 11 dB(A) higher than the ambient
noise with a averaged signal to noise ratio for communication of about 10 dB(A).
Conclusions: The left ear is more susceptible than the right ear to hearing loss. Active
noise reduction systems allow for a reduced sound level for the communication signal
below the upper exposure action value of 85 dB(A) and allow for a more relaxed
working environment for pilots.
Strengths and limitations of this study
The current study is a large epidemiological study in civilian pilots over a wide age span
with acoustic measurements in various airplanes.
Hearing thresholds include extended high frequencies.
Multivariate analysis and differential presentation (left-right ear) identified unknown risk
factors influencing hearing thresholds.
A limitation is the cross-sectional design of the study.
Page 2 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
3
INTRODUCTION
Civilian airline pilots bear a high responsibility as one wrong decision could lead to
disastrous consequences for the entrusted employees and passengers. The demands on the
health and performance of pilots are correspondingly high. Communication and the
understanding of acoustic information are very important in their occupation and a
sufficiently good hearing is one of the fundamental conditions for the profession. Therefore a
hearing test at the annual health check-ups is mandatory. Nevertheless, sound exposure for
pilots and the consequences for their hearing is still being discussed.
Modern jet aircrafts are less noisy than former models. This results in reduced noise exposure in
the flight cabin and less annoyance for the affected population. However, the reduced
annoyance per flight will be overcompensated by a higher flight frequency. Lindgren et al. [1]
for example did not find an extended risk to hearing loss in Swedish airline pilots compared to a
non-noise exposed population. The upper action values of 85 dB(A) were generally not
reached. They also found about 1.2 dB worse thresholds in the left ear when compared to the
right ear. Lie et al. [2] reported in a review about occupational noise exposure no articles with
markedly increased risk to hearing impairment in civilian airline pilots. However there are hints
about an increased susceptibility to hearing loss of the left ear compared to the right, which are
independent of the occupation [3, 4]. In studies to the hearing of pilots the left-right ear
asymmetries are considered only negligible. This subject will be addressed in the present study.
Presbyacusis is one main factor for a decreasing hearing ability over age. Therefore it is
desirable to eliminate the age factor from the audiometric data so as to discover other factors
like occupational and environmental noise exposure of the pilots. This can be done by using
existing standards to a suitable age correction. The usefulness of age correction standards
will be demonstrated in the present paper.
Page 3 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
4
METHODS
Study Population
Civilian pilots of a large German airline were examined during the annual health check-ups
with particular attention to their hearing status. All pilots were interviewed in a standardized
manner about their professional and leisure -related noise exposures. From a total of 542
candidates, 487 male pilots were included in the study. 12 pilots were excluded because their
questionnaires were lost or incomplete. Further 12 people were excluded, because they did
not work in the cockpit and the 5 female pilots were excluded because the subgroup was too
small. Furthermore, 11 pilots were excluded due to sudden hearing loss, 12 due to former ear
surgery and 3 because of severe colds. So about 10 % of the examined subjects (55 out of
542) were not involved in the analysis. The mean age was 43 years (median: 38 years), with
a range from 20 (pilot candidates) to 63 years. Since a strong age dependency of the
audiograms was to be expected, the pilots were divided in two age groups. 271 pilots were
younger than 40 years old with 11 flight alumni, 209 flight officers, 48 captains and 3 flight
engineers. 216 pilots were 40 years and older with 14 flight officers, 180 captains and 25
flight engineers. The mean age of the younger group was 32.4 years and of the older group
48.8 years. The mean difference of age therefore was 16.4 years. Four age groups with ten
year range were pooled for statistical characteristics (percentiles).
Instrumentation, Material
Pure tone audiometry was performed by experienced audiologist’s assistants in a sound proof
room of the medical center of the airline company. The audiometer was a type CA540 from
Hortmann GmbH (now GN-Otometrics) with circum-aural headphones type HDA200 from
Sennheiser suitable for tests in the extended high frequency range up to 16 kHz. The
maximum sound levels of the CA540 in combination with the HDA200 are 90 dB HL at
11.2 kHz, 80 dB HL at 12.5 kHz, 70 dB HL at 14 kHz and 60 dB HL at 16 kHz (HL:
hearing level according to ISO 389-5 and ISO 389-8)[5, 6]. Via the serial interface RS 232
the audiometric data were recorded into a software database Avantgarde 2.0 of the company
Nüß (Hamburg).
Acoustic Measurements
The acoustic measurements in aircraft cockpits were carried out by the technical service of
the aviation company. The measurements were performed with a ½ inch free-field
microphone and an acoustic manikin Type 4100 with an artificial middle ear Type 4157 of
Brüel & Kjær (Denmark). In all sound measurements integrating function and an A-filter
were used, as it corresponds to the regulations in the EU DIRECTIVE 2003/10/EC [7]. The
free-field microphone was placed beside the pilot near the ear. The acoustic manikin was
placed on a seat just behind the pilot wearing a headset in the same way as the pilot receiving
the same signal. The headset was a two-sided supra-aural headphone without active noise
attenuation. The middle ear simulator conforms to IEC 60318-4, ANSI 3.25 and ITU-T Rec.
P.47. The frequency response and impedance is similar to the real human ear.
Page 4 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
5
Age-correction
Presbyacusis is the main influence factor in hearing thresholds if the study collective differs
widely in age. To analyze other factors it is advisable to eliminate the age factor from the
dataset. The success of this procedure depends on the validity of the used age correction tool.
The ISO 7029 (2000)[8] is still valid but a new draft of ISO 7029 (2014) has new correction
formulas leading to different results. The usage of age correction tables (examples of
database B) in ISO 1999 (2013) [9] is also not helpful, because the three examples differ
more than the two versions of ISO 7029 [8]. The results and their interpretations depend on
the decision of which version is used and become arbitrary. In the current study we will
demonstrate the difference of both versions of ISO 7029 [8] and renounce on the statistical
analysis of age-corrected threshold data. The focus of the paper was placed on individual
left-right threshold differences because they do not require age-correction.
Software and Statistics
All data were calculated with Excel 2013 in particular the age correction. Simple T-tests
were implemented in Excel to get hints for further evaluation. A comprehensive multi-
factorial ANOVA with repeated measures was calculated using SPSS 20.
Page 5 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
6
RESULTS
Hearing Thresholds
The audiometric examinations of jet pilots from a German airline company are presented as
average audiograms in age-groups, hereby evaluating both ears and the averaged differences
between both ears. In Fig. 1a the averaged thresholds of all pilots in the age groups and both
ears are presented in the upper part and the left-right differences in the lower part Fig 1b. The
results are two completely separated curves clearly indicating better hearing for younger
pilots. At low frequencies up to 1.5 kHz the curves are parallel with differences between 2
and 4 dB. From 2 kHz up to 14 kHz the differences increase up to about 30 dB. The 16 kHz
value in the older group is distorted by missing data caused by the limitations of the
audiometer. Fig. 1b shows small threshold differences < ± 1 dB between both ears up to 2
kHz. Here both curves cross the zero level from “right ear worse” to “left ear worse” with
increasing values. The curve of the younger pilots does not exceed levels over ± 2 dB. In the
older pilots the threshold difference increases up to 6 dB at 6 kHz. The 8 kHz value seems to
be a local minimum in both age groups. In the extended frequency range the differences
between right and left ear decreases and approach each other at 16 kHz at about 1 dB.
{Fig. 1}
Tab. 1: Distribution of hearing levels averaged across left and right ears (dB HL) in four age-
groups.
Frequency Centile Age (years)
20–29 30–39 40–49 50–59
3 kHz 10 -5.0 -2.5 0.0 2.5
25 0.0 0.0 2.5 7.5
Median 0.0 2.5 7.5 11.3
75 5.0 5.0 12.5 17.5
90 10.0 10.0 20 25.8
4 kHz 10 0.0 0.0 3.3 7.5
25 0.0 2.5 7.5 12.5
Median 5.0 5.0 12.5 17.5
75 10.0 10.0 19.4 26.9
90 17.5 15.0 27.5 35.0
6 kHz 10 0.0 0.0 5.0 7.5
25 5.0 5.0 10.0 12.5
Median 10.0 7.5 13.8 21.3
75 15.0 12.5 22.5 29.4
90 20.0 17.5 35.0 37.5
N 74 197 133 77
In Tab. 1 the statistical distribution in the frequencies 3, 4 and 6 kHz is presented in four age-groups
with a span of ten years. 6 pilots are between 60 and 63 years old and not considered in the
distribution.
Page 6 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
7
Age-corrected thresholds
The effect of two different age corrections can be seen in Fig. 2. The 2nd edition of ISO 7029
[8] is presented in Fig. 2a and the 3rd draft edition in Fig. 2b. Frequency range is limited to
125 Hz up to 12.5 kHz the highest correction proposal in the 3rd draft edition.
{Fig. 2}
Altogether the new version of the ISO 7029 indicates a smaller influence of aging on hearing
thresholds, especially in the frequency range from 3 to 6 kHz where the influence of noise
(ISO 1999) is most pronounced. The threshold levels of the younger pilots differed only a
little (≤ 2 dB) while in the older pilots the thresholds increased to 3.5 dB at 4 kHz, 6 dB at 4
kHz, 5 dB at 6 kHz and 7 dB at 8 kHz. The better hearing in older pilots in Fig. 2a shifts to a
worse hearing in Fig. 2b by different age correcting factors according to ISO 7029 [8].
Page 7 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
8
Cockpit Noise and Communication Sound
For nine jet models of a German airline, free field noise measurements were carried out in
the cockpit (Hoffmann 2004) [10], which were supplemented by acoustic manikin
measurements. The free-field measurements yielded values between 74 dB(A) for the B767
and 80 dB(A) for B747 jets. The sound pressure levels for communication are higher than
the ambient noise for a clear understanding of the messages. These sound pressure levels
were measured with an acoustic manikin under the headset to estimate effects on hearing. In
Tab. 2 these measurement data are presented with measurement times and the time portion
with communication (ATC) in minutes. In contrast to the uniformly ambient noise the
communication signal fluctuates and contains impulsive parts of sound. Therefore the
measurements with time constant “fast” (125 ms) were supplemented by measurements with
the time constant “impulse” (attack time 35 ms, release time 1.5 sec.).
Tab. 2: Sound pressure level measurements in 9 different jet cockpits. Free field ambient
noise (AN) measurement data during flight time are presented as well as data from an acoustic
manikin (AM). Measurement data from Hoffmann [10]. AMcATC are calculated values by
using the ISO 11904-2 [11] and the ATC time.
Jet Data Sound Pressure Data
Type Flight time ATC time ANFt AMfFt AMiFt AMcATC SNR
minutes minutes dB(A)f dB(A)f dB(A)i dB(A)f dB(A)
A310-200 162 70 74.9 81.9 87.9 83.5 8.6
A310-300 460 208 76.7 86.7 92.7 88.1 11.4
B737-200 221 81 76.8 81.4 87.4 83.8 7.0
B737-300 137 28 77.3 80.9 85.9 85.8 8.5
B747 1144 344 79.9 84.8 89.9 88.0 8.1
B757 357 134 75.1 83.7 89.9 86.0 10.9
B767 294 112 74.4 81.6 87.9 83.8 9.4
DC10 116 50 76.8 85.9 91.2 87.6 10.8
MD11 153 73 75.0 84.6 90.3 85.8 10.8
ATC(air trafic control), Ft(Flight time), AN(free field ambient noise), AM(acoustic manikin), SNR(signal to noise ratio)
dB(A)f(sound pressure level with A-weighting and time constant: fast), dB(A)i(with time constant: impulse)
AMcATC (spectral corrected values of AMfFt by ISO 11904-2 and calculated to the ATC time).
The differences between „impulse“and „fast“ measurements with the acoustic manikin
(AMiFt – AMfFt) are between 5 and 6 dB indicating an impulsive character of the
communication sound. With the time period of air traffic control (ATC) compared to the
total flight time the equivalent sound exposure of the pilots during communication can be
estimated after a spectral correction according to ISO 11904-2 [11]. This was done in the
column AMcATC. The difference between AMcATC and the ambient noise (ANFt) is the
signal to noise ratio (SNR) for communication. This value varies between minimal 7 dB and
maximal 11 dB. The average is about 10 dB.
The free field measured ambient noise in Airline cockpits does not reach the lower exposure
action values of 80 dB(A) of the EU DIRECTIVE 2003/10/EC [7] if the flight time is below
8 hours. The corrected sound pressure levels of communication sound AMc(ATC) exceeds the
Page 8 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
9
upper exposure action value of the directive of 85 dB(A) in 6 cases for a flight times of 8
hours and more. The minimum communication sound level was calculated to 83.5 dB(A) in
the Airbus A320-200, and the maximum level to 88.1 dB(A) in the Airbus A310-300. Only
in intercontinental flights the flight time reaches or exceeds 8 hours.
Statistics
With a multi-factorial ANOVA with repeated measures, the left-right differences in the
threshold data were statistically evaluated for possible influencing factors (see Tab. 3). In
addition to the age group, four other dichotomous factors were selected, which suggests an
impact on the development of noise-induced hearing deteriorations as there are: acoustic
shocks, military service, attending discos, and the use of hearing protectors at noisy leisure
activities. The usage of the headset for communication has three options: right ear, left ear or
both ears.
Tab. 3: Statistical analysis. ANOVA concerning threshold differences (left – right) with 6
between groups factors: age group, acoustic shocks, military service, disco visits, use of ear
protectors and use of the communication headset. One within groups factor is the frequency.
Analyzed were 3, 4 and 6 kHz, which are predominantly affected by noise.
between groups df F p
AgeGrp 1 8.711 0.003
AcousticShock 1 1.838 0.160
Military 1 0.142 0.707
Disco 1 0.672 0.413
EarProt 1 1.654 0.199
HeadsetEar 2 8.685 <0.001
within groups
Frequency 2 5.473 0.020
Frequency * AgeGrp 2 6.111 0.014
Significant factors and interactions (*) are expressed bold
The factor age group shows significant increasing differences between both ears and the factor
headset ear shows a significant effect (p<0.001) on the worse hearing of the left ear.
The within-subjects factor contains the three frequencies 3, 4 and 6 kHz, which have the
strongest effect of noise according to ISO 1999 [9] and is significant at p=0.02. Only 2-way
interactions between frequency and the other main factors were determined. With the exception
of “frequency x age group” all interactions are not significant and are not listed in Tab. 3.
Page 9 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
10
Headset
The dominant part of noise exposures results from communication sound as seen in Tab. 2.
More than half of the pilots (N=276) use the headset on both ears, while the others prefer to
use only one ear for radio communication.
{Fig. 3}
The preferred headset usage in the age groups is presented in Fig. 3. More than half of the
pilots (57 %) used both ears for radio communications. About a third (34 %) preferred to use
only the right ear and 9 % only the left ear. The pilots with left ear preference were all
captains sitting on the left seat with the right ear free for normal cockpit communication. 43
of these captains were older than 40 years and only 2 of them younger.
{Fig. 4}
In Fig. 4 the effects of this different behavior on the threshold differences between the ears is
presented. Between pilots with the headset on both ears and the right ear the curves are close
together. Only at 4 kHz the difference exceeds 1 dB in the standard frequency range up to 8
kHz. The pilots who prefer to use the left ear for communication tasks, show a conspicuous
worse hearing at the left ear in the analyzed frequencies with more than 7 dB at 6 kHz. At 8
kHz the effect is noticeably smaller and increases in the extended high range between 9 and
11 kHz. The 12.5 kHz threshold difference decreases to a value of about 3 dB.
Page 10 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
11
DISCUSSION
As expected, the age of the pilots is the main influence factor on the hearing ability. Fig. 1a
shows a clear separation of the two age group curves. At frequencies above 2 kHz the age
dependent differences increase. The course at 14 and 16 kHz is affected by lack of
measurements in older pilots by the limited sound pressure level of the audiometer at these
frequencies. The threshold differences between left and right ear (Fig. 1b) show a clear
tendency to worse hearing of the left ear. This tendency is most pronounced at frequencies 3 –
6 kHz and 9 – 11 kHz in both age groups and much stronger in the older pilots. At lower
frequencies (< 3 kHz) the difference values oscillate around the zero line within a ± 1 dB
range. At 1 kHz both age groups show better hearing by 1 dB of the left ear and no
dependence on age.
Age adjustment in accordance with ISO 7029 [8] should eliminate the age-related effects
from the data. The Fig. 2 shows the results of two versions of ISO 7029 [8]. The second edition
in Fig. 2a from 2000 shows a stronger dependence of the age than the new draft edition in
Fig. 2b from 2014. In the case of our dataset we get reverse results in the interesting frequency
range 3 – 6 kHz. Age corrected with the second edition the older pilots hear better and a
positive influence of the noise situation would be concluded. With the third edition the younger
pilots hear better and we recognize hearing loss. While the third edition represents a draft and
the second edition is still valid we recognize the closer outcomes of our study with the new
ISO 7029 [8] version.
In Tab. 1 the distribution of threshold measurements are presented. Compared to the
screened dataset of Engdahl et al.[12] the percentiles of our data are lower on an average of
4.5 dB and the 80 % span in our dataset is smaller on an average of 9 dB.
The free-field sound data of Hoffmann [10] in Tab. 2 in aircraft cockpits show sound
pressure levels between 74 dB(A) and 80 dB(A). Lindgren et al[1] published lower values
between 71 dB(A) and 76 dB(A). Begault [13] described higher values between 75 dB(A) for
the Airbus A 310 and 84 dB(A) for the Boeing B 727. The ambient noise in cockpits reported
by Lower and Bagshaw [14] had levels between 71 and 79 dB(A). The values of Hoffmann
[10] are in between this measurement data sets from literature. None of the free field sound
pressure levels of the ambient noise reach the upper exposure action value of 85 dB(A). If we
take into account, that noise with impulsive character is more harmful than pure continuous
noise, for noise exposure levels by communication the “impulse” weighted exposure levels
could be used. In all cases the upper exposure action values then would be reached during
communication. As the ATC time is mostly shorter than half of the total flight time and
never 8 hours, the higher exposure levels will be compensated approximately by the shorter
exposure time. The equivalent exposure levels of our pilots are than around the upper
exposure action value of 85 dB(A) in 8 hours.
Gassaway[15] has identified significantly higher values in cockpits of propeller aircraft from
an average of 95 dB(A) and strongly recommended the use of hearing protection. Military
aircraft are usually even louder. Overall, these measurements are not directly comparable,
since the measured aircraft are not the same and certainly also vary in the cockpit design and
the measurement setup.
Page 11 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
12
The noise exposure level caused by the radio communication exceeds the ambient cockpit
noise, because the messages have to be understood completely. In tests for speech-in-noise
recognition mostly a 50 % criterion is used to determine the normal skill [16]. At sound
pressure levels of 83 dB SPL Killion et al. [17] found a word recognition score of 50 % at a
corresponding signal-to-noise ratio of about 2 dB. Pilots need full understanding of the
messages at much higher SNR values. The largely standardized communication in aviation
has a high redundancy in the transferred messages, what reduces the required SNRs. In the
current study the average SNR used by the pilots was at 10 dB, obviously enough for a
recognition rate of about 100 %. Lower and Bagshaw [14] measured spectral corrected sound
levels for communication between 80 and 88 dB(A). Compared with the corresponding
ambient noise levels SNR values between 6 and 13 dB(A) can be calculated with an average
of about 10 dB(A) like in our dataset.
Circum-aural headsets with passive sound attenuation can be helpful to reduce the
communication sound levels, but they impede the communication between the crew as the
attenuation at high frequencies is much better than at low frequencies in those earphones.
Headsets with active noise reduction (ANR) systems are now commonly installed, which
reduces predominantly the masking low- frequency noise of the cockpit [18, 19]. The sound
pressure level of the radio-communication can substantially be reduced to a level below the
lower exposure action value of 80 dB(A). The pilots of the current study did not use any
hearing protection systems. The protective effect depends on wearing the headset on both
ears. Open headsets with low frequency noise reduction may allow communication between
captain and flight officer as the masking effects are reduced.
211 of the 487 pilots had a preference to use the communications headset mostly on only one
ear. This subgroup is suited to analyze the effect of radio communication on hearing. 166
pilots preferred the right ear, 45 pilots the left ear and 276 used both ears. Fig. 4 shows
significant differences between these groups. The differences between pilots who use both ears
and predominantly the right ear for communication are quite small (max. at 4 kHz 1.3 dB). The
left ear, however, shows significant greater differences with more than 7 dB at 6 kHz. In
Tab. 1 this fact can be seen as the strongest effect of the ANOVA for headset usage with
p < 0.001. With the exception of two pilots all of these pilots are in the older age group. This
asymmetry can be recognized in Fig. 1b in the older age group to a lesser degree as in Fig. 4
where the subgroup with left ear preference is particularly striking.
The right ear seems to be more resistant against the effects of noise than the left ear, because
the pilots with headset at the right ear almost do not differ significantly from those with
headset at both ears. Left-right ear threshold asymmetries are described by Pirilä et al. [3]. In
the frequency range between 3 and 6 kHz these authors found higher thresholds on the left
ear and concluded a greater susceptibility to noise induced hearing loss of the left ear as a
biological effect. Influences like handedness and the audiometric test procedure with
learning and fatigue effects could be excluded [20, 21, 22]. This effect was also present in
females to a lesser degree, because they are in general less exposed to noise. The higher left-
right differences in Cruickshanks et al. [4] may result from not excluding the users of
firearms from their dataset.
The pilot group who used both ears for communication tasks show no increased damaging
Page 12 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
13
effect at the left ear, although both ears had the same sound exposure level. A possible
explanation of this result could be the advantage of the binaural hearing [23] with the
squelch-effect (summation of interesting sound and unmasking of the noise) what leads to
reduced communication sound levels at a given ambient noise.
Based on the present findings, it can be concluded that the pilots of civil aviation have a good
hearing ability compared to other industrial workers with comparable noise exposure levels.
The left ear shows markedly higher risk of hearing damage than the right ear. If this effect is
age dependent cannot be answered with the current dataset. The use of headsets with active or
passive noise reduction at both ears can solve this last problem and may eliminate any risk for
hearing loss in pilots during their normal occupational activity. The hint to pilots to allways
use both ears for communication and never use only the left ear may also be helpful.
Page 13 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
14
Acknowledgements
The authors thank Gerald Fleischer for his ideas and suggestions as well as the management
of data collection in the Lufthansa service center in Frankfurt/Main. Also many thanks to
Knut Hoffmann of Lufthansa Technik in Hamburg for the measurement data in jet cockpits.
Conflict of interest declaration
The authors declare no conflict of interest.
Data sharing statement
No additional data available.
Funding statement
No funding.
Ethics statement
The data collection in this non-interventional study was part of the annual health check-up’s
within the German occupational safety and health system (health check for pilots enforced by
law). As individuals participated voluntarily in the study and all data were analyzed
anonymously, no ethical approval was required, in accordance with German guidelines.
Contributorship statement
Conception and design: Reinhard Müller and Joachim Schneider
Administrative support: Reinhard Müller
Provision of study materials and patients: Reinhard Müller
Collection and assembly of data: Reinhard Müller
Data analysis and interpretation: Reinhard Müller and Joachim Schneider
Manuscript writing: Reinhard Müller and Joachim Schneider
Final approval of manuscript: Reinhard Müller and Joachim Schneider
Page 14 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
15
References
1. Lindgren T, Wieslander G, Dammström BG, Norbäck D. Hearing status among
commercial pilots in a Swedish airline company. Int J Audiol. 2008;47:515–519
2. Lie A, Skogstad M, Johannessen HA, Tynes T, Mehlum IS, Nordby KC, Engdahl B
and Tambs K. Occupational noise exposure and hearing: a systematic review. Int Arch
Occup Environ Health 2016; 89:351–372.
3. Pirilä T, Jounio-Ervasti K, Sorri M. Left-right asymmetries in hearing threshold levels
in three age groups of a random population. Audiology 1992;31:150–161.
4. Cruickshanks KJ, Wiley TL, Tweed TS, Klein BEK, Klein R, Mares-Perlman JA and
Nondahl DM. Prevalence of hearing loss in older adults in Beaver Dam, Wisconsin:
the epidemiology of hearing loss study. Am J Epidemiol. 1998;148(9):879–886.
5. ISO 389-5. Acoustics – Reference zero for the calibration of audiometric equipment
– Part 5: Reference equivalent threshold sound pressure levels for pure tones in the
frequency range 8 kHz to 16 kHz. Geneva, Switzerland: International Organization
for Standardization. 1999.
6. ISO 389-8. Acoustics – Reference zero for the calibration of audiometric equipment –
Part 8: Reference equivalent threshold sound pressure levels for pure tones and circum-
aural earphones. Geneva, Switzerland: International Organization for Standardization.
2004.
7. EU DIRECTIVE 2003/10/EC OF THE EUROPEAN PARLIAMENT AND OF
THE COUNCIL (2007)
8. ISO 7029. Acoustics – Statistical distribution of hearing thresholds as a function of age.
Geneva, Switzerland: International Organization for Standardization. 2000.
9. ISO 1999. Acoustics – Estimation of noise induced hearing loss. Geneva, Switzerland:
International Organization for Standardization. 2013.
10. Hoffmann K. Sound measurements in cockpits of civilian aircraft. 2004. Not poblished
data received as personal communication.
11. ISO 11904-2. Acoustics – Determination of sound immissions from sound sources
placed close to the ears – Part 2: Technique using a manikin. Geneva, Switzerland:
International Organization for Standardization. 2004.
12. Engdahl B, Tambs K, Borchgrevink HM, Hoffman HJ. Screened and unscreened
hearing threshold levels for an adult population: Results from the Nord-Trøndelag
Hearing Loss Study. Int J Audiol. 2005; 44:213–230
13. Begault DR, Wenzel EM. Assessment of noise exposure in commercial aircraft
cockpits (interim report). 1998; Available online at: http:/human-
factors.arcnasa.gov/publibary/Begault_1998_Noise_in_Cockpit.pdf.
14. Lower MC, Bagshaw M. Noise levels and communication on the flight decks of civil
aircraft. 25th Internoise proc. 1996.
Page 15 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
16
15. Gasaway DC. Noise levels in cockpits of aircraft during normal cruise and
considerations of auditory risk. Aviat Space Environ Med. 1986;57: 103–112.
16. Thibodeau LM. Speech Audiometry. In Roeser JR, Valente M and Hosford-Dunn
H. Audiology. 2nd Ed. Thieme, 2007. New York, Stuttgart
17. Killion MC, Niquette PA, Gudmundsen GI. Development of a quick speech- in-noise
test for measuring signal-to-noise ratio loss in normal-hearing and hearing-impared
listeners. J Acoust Soc Am. 2004;116(4):2395–2405.
18. Matschke RG. Communication and noise Speech intelligibility of aircraft pilots with
and without electronic compensation for noise. HNO. 1994;42:499–504.
19. Casali JG. Powered Electronic Augmentations in Hearing Protection Technology Circa
2010 including Active Noise Reduction, Electronically-Modulated Sound Transmission,
and Tactical Communications Devices: Review of Design, Testing, and Research.
International Journal of Acoustics and Vibration. 2010;15(4): 168–186.
20. Pirilä T, Jounio-Ervasti K, Sorri M. Hearing asymmetry among left-handed and right-
handed persons in a random population. Scand. Audiol. 1991;20:223–226.
21. Axelsson A, Jerson T, Lindberg U, Lindgren F. Early noise-induced hearing loss in
teenaged boys. Scand. Audiol. 1981;10:91–96.
22. Borod J, Obner L, Albert M, Stiefel S. Lateralization for pure tone perception as a
function of age and sex. Cortex 1983;19:281–285.
23. Arsenault MD, Punch JL. Nonsense-syllable recognition in noise using monaural and
binaural listening strategies. J Acoust Soc Am. 1999;105(3):1821–1830.
Figures
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears
averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal
hearing levels (dB HL). Part b shows the differences between left and right ear in dB.
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are
age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3
rd
draft (lower part b)
Fig. 3: Age groups and preferred headset usage.
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred
headset usage from 125 Hz up to 12.5 kHz.
Page 16 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal hearing levels (dB HL). Part b
shows the differences between left and right ear in dB.
Page 17 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3rd draft (lower part b)
Page 18 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 3: Age groups and preferred headset usage.
Page 19 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred headset usage from 125 Hz up to 12.5 kHz.
130x72mm (300 x 300 DPI)
Page 20 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
1
Statement—Checklist
Item
No Recommendation
On
Page
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 1
(b) Provide in the abstract an informative and balanced summary of what was done
and what was found
2
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 3
Objectives 3 State specific objectives, including any prespecified hypotheses 3
Methods
Study design 4 Present key elements of study design early in the paper 4
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,
exposure, follow-up, and data collection
4
Participants 6 (a) Give the eligibility criteria, and the sources and methods of selection of
participants
4
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect
modifiers. Give diagnostic criteria, if applicable
-
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of
assessment (measurement). Describe comparability of assessment methods if there
is more than one group
-
Bias 9 Describe any efforts to address potential sources of bias -
Study size 10 Explain how the study size was arrived at 4
Quantitative
variables
11 Explain how quantitative variables were handled in the analyses. If applicable,
describe which groupings were chosen and why
-
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 5
(b) Describe any methods used to examine subgroups and interactions 9
(c) Explain how missing data were addressed -
(d) If applicable, describe analytical methods taking account of sampling strategy -
(e) Describe any sensitivity analyses -
Results
Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially
eligible, examined for eligibility, confirmed eligible, included in the study,
completing follow-up, and analysed
4, 10
(b) Give reasons for non-participation at each stage 4
(c) Consider use of a flow diagram -
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and
information on exposures and potential confounders
-
(b) Indicate number of participants with missing data for each variable of interest -
Outcome data 15* Report numbers of outcome events or summary measures -
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and
their precision (eg, 95% confidence interval). Make clear which confounders
were adjusted for and why they were included
-
(b) Report category boundaries when continuous variables were categorized -
(c) If relevant, consider translating estimates of relative risk into absolute risk for a
meaningful time period
-
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and
sensitivity analyses
-
Page 21 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
Discussion
Key results 18 Summarise key results with reference to study objectives
Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or
imprecision. Discuss both direction and magnitude of any potential bias
11
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,
multiplicity of analyses, results from similar studies, and other relevant evidence
12
Generalisability 21 Discuss the generalisability (external validity) of the study results 13
Other information
Funding 22 Give the source of funding and the role of the funders for the present study and, if
applicable, for the original study on which the present article is based
-
*Give information separately for exposed and unexposed groups.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published
examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the
Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and
Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
Page 22 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Noise exposure and auditory thresholds of German airline
pilots. A cross sectional study.
Journal: BMJ Open
Manuscript ID bmjopen-2016-012913.R4
Article Type: Research
Date Submitted by the Author: 24-Feb-2017
Complete List of Authors: Müller, Reinhard; Universitätsklinikum Giessen und Marburg, Institut und Poliklinik für Arbeits- und Sozialmedizin
Schneider, Joachim; Universitatsklinikum Giessen und Marburg Standort Giessen, Institut und Poliklinik für Arbeits- und Sozialmedizin
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Ear, nose and throat/otolaryngology
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, Audiology < OTOLARYNGOLOGY, Noise and Health
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open on M
ay 2, 2020 by guest. Protected by copyright.
http://bmjopen.bm
j.com/
BM
J Open: first published as 10.1136/bm
jopen-2016-012913 on 30 May 2017. D
ownloaded from
For peer review only
Noise exposure and auditory thresholds of German airline pilots.
A cross sectional study.
Dr. Reinhard Müller1 and Prof. Dr. Joachim Schneider
2
1,2) Institut und Poliklinik für Arbeits- und Sozialmedizin am Universitätsklinikum
Giessen und Marburg.
1) Corresponding Author:
Dr. Reinhard Müller
IPAS Akustiklabor
Justus-Liebig-Universität Giessen
Aulweg 123
35392 Giessen
Germany
Fon: +49 641 9941316
Fax: +49 641 9941319
Mail: [email protected]
Keywords:
cockpit noise, hearing thresholds, influencing factors, left-right ear asymmetries, signal to
noise ratio
What this paper adds:
The cross sectional study in airline pilots shows that a pilots sense of hearing is likely to be
significantly more impaired on the left ear. The cause of this is probably their exposure to
high sound levels of communication with headsets to which the left ear seems to be more
susceptible to damage.
Page 1 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
ABSTRACT
Objective: The cockpit workplace of airline pilots is a noisy environment. This study
examines the hearing thresholds of pilots with respect to ambient noise and
communication sound.
Methods: The hearing of 487 German pilots was analyzed by audiometry in the
frequency range of 125 Hz – 16 kHz in varying age-groups. Cockpit noise (free-field)
data and communication sound (acoustic manikin) measurements were evaluated.
Results: The ambient noise levels in cockpits were found to be between 74 dB(A) and
80 dB(A) and the sound pressure levels under the headset were found to be between 84
dB(A) and 88 dB(A).
The left-right threshold differences at 3, 4 and 6 kHz show evidence of impaired hearing
at the left ear, which worsens by age.
In the age-groups <40/≥40 years the mean differences at 3 kHz are 2/3 dB, at 4 kHz
2/4 dB and at 6 kHz 1/6 dB.
In the pilot group which used mostly the left ear for communication tasks (43 of 45 are in
the older age group) the mean difference at 3 kHz is 6 dB, at 4 kHz 7 dB and at 6 kHz
10 dB. The pilots who used the headset only at the right ear also show worse hearing at
the left ear of 2 dB at 3 kHz, 3 dB at 4 kHz and at 6 kHz. The frequency corrected
exposure levels under the headset are 7 to 11 dB(A) higher than the ambient noise with a
averaged signal to noise ratio for communication of about 10 dB(A).
Conclusions: The left ear seems to be more susceptible to hearing loss than the right
ear. Active noise reduction systems allow for a reduced sound level for the
communication signal below the upper exposure action value of 85 dB(A) and allow for
a more relaxed working environment for pilots.
Strengths and limitations of this study
The current study is a large epidemiological study in civilian pilots over a wide age span
with acoustic measurements in various airplanes.
Hearing thresholds include extended high frequencies.
Multivariate analysis and differential presentation (left-right ear) identified unknown risk
factors influencing hearing thresholds.
A limitation may be the cross-sectional design of the study without the direct development
of hearing loss in the individuals.
Page 2 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
3
INTRODUCTION
Civilian airline pilots bear a high responsibility as one wrong decision could lead to
disastrous consequences for the entrusted employees and passengers. The demands on the
health and performance of pilots are correspondingly high. Communication and the
understanding of acoustic information are very important in their occupation and a
sufficiently good hearing is one of the fundamental conditions for the profession. Therefore a
hearing test at the annual health check-up is mandatory. Nevertheless, sound exposure for
pilots and the consequences for their hearing is still being discussed.
Modern jet aircrafts are less noisy than former models. This results in reduced noise exposure in
the flight cabin and less annoyance for the affected population. However, the reduced
annoyance per flight will be overcompensated by a higher flight frequency. Lindgren et al. [1]
for example did not find an extended risk to hearing loss in Swedish airline pilots compared to a
non-noise exposed population. The upper action values of 85 dB(A) were generally not
reached. They also found about 1.2 dB worse thresholds in the left ear when compared to the
right ear. Lie et al. [2] reported in a review about occupational noise exposure no articles with
markedly increased risk to hearing impairment in civilian airline pilots. However there are hints
about an increased susceptibility to hearing loss of the left ear compared to the right, which are
independent of the occupation [3, 4]. In studies concerning the hearing of pilots the left-right
ear asymmetries are considered only negligible. This subject will be addressed in the present
study.
Presbyacusis is one main factor for a decreasing hearing ability over age. Therefore it is
desirable to eliminate the age factor from the audiometric data so as to discover other factors
like occupational and environmental noise exposure of the pilots. This can be done by using
existing standards to a suitable age correction. The usefulness of age correction standards
will be demonstrated in the present paper.
Page 3 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
4
METHODS
Study Population
Civilian pilots of a large German airline were examined during the annual health check-ups
within the German occupational safety and health system (health check for pilots are
enforced by law) with particular attention to their hearing status. All voluntarily participating
pilots were interviewed in a standardized manner about their professional and leisure-related
noise exposures. From a total of 542 candidates, 487 male pilots were included in the study.
12 pilots were excluded because their questionnaires were lost or incomplete. Further
12 people were excluded, because they did not work in the cockpit and 5 female pilots were
excluded because the subgroup was too small. Furthermore, 11 pilots were excluded due to
sudden hearing loss, 12 due to former ear surgery and 3 because of severe colds. So about
10 % of the examined subjects (55 out of 542) were not involved in the analysis. The mean
age was 43 years (median: 38 years), with a range from 20 (pilot candidates) to 63 years.
Since a strong age dependency of the audiograms was to be expected, the pilots were divided
in two age groups. 271 pilots were younger than 40 years old with 11 flight alumni, 209 flight
officers, 48 captains and 3 flight engineers. 216 pilots were 40 years and older with 14 flight
officers, 180 captains and 25 flight engineers. The mean age of the younger group was 32.4
years and of the older group 48.8 years. The mean difference of age therefore was 16.4 years.
Four age groups with ten year range were pooled for statistical characteristics (percentiles).
Instrumentation, Material
Pure tone audiometry was performed by experienced audiologist’s assistants in a sound proof
room of the medical center of the airline company. The audiometer was a type CA540 from
Hortmann GmbH (now GN-Otometrics) with circum-aural headphones type HDA200 from
Sennheiser suitable for tests in the extended high frequency range up to 16 kHz. The
maximum sound levels of the CA540 in combination with the HDA200 are 90 dB HL at
11.2 kHz, 80 dB HL at 12.5 kHz, 70 dB HL at 14 kHz and 60 dB HL at 16 kHz (HL:
hearing level according to ISO 389-5 and ISO 389-8)[5, 6]. Via the serial interface RS 232
the audiometric data were recorded into a software database Avantgarde 2.0 of the company
Nüß (Hamburg).
Acoustic Measurements
The acoustic measurements in aircraft cockpits were carried out by the technical service of
the aviation company. The measurements were performed with a ½ inch free-field
microphone and an acoustic manikin Type 4100 with an artificial middle ear Type 4157 of
Brüel & Kjær (Denmark). In all sound measurements integrating function and an A-filter
were used, as it corresponds to the regulations in the EU DIRECTIVE 2003/10/EC [7]. The
free-field microphone was placed beside the pilot near the ear. The acoustic manikin was
placed on a seat just behind the pilot wearing a headset in the same way as the pilot and
receives the same signal. The headset was a two-sided supra-aural headphone without active
noise attenuation. The middle ear simulator conforms to IEC 60318-4, ANSI 3.25 and ITU-
T Rec. P.47. The frequency response and impedance is similar to the real human ear.
Page 4 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
5
Age-correction
Presbyacusis is the main influence factor in hearing thresholds if the study collective differs
widely in age. To analyze other factors it is advisable to eliminate the age factor from the
dataset. The success of this procedure depends on the validity of the used age correction tool.
The ISO 7029 (2000)[8] is still valid but a new draft of ISO 7029 (2014) has new correction
formulas leading to different results. The usage of age correction tables (examples of
database B) in ISO 1999 (2013) [9] is also not helpful, because the three examples differ
more than the two versions of ISO 7029 [8]. The results and their interpretations depend on
the decision of which version is used and become arbitrary. In the current study we will
demonstrate the difference of both versions of ISO 7029 [8] and renounce on the statistical
analysis of age-corrected threshold data. The focus of the paper was placed on individual
left-right threshold differences because they do not require age-correction.
Software and Statistics
All data were calculated with Excel 2013 in particular the age correction. Simple T-tests
were implemented in Excel to get hints for further evaluation. A comprehensive multi-
factorial ANOVA with repeated measures was calculated using SPSS 20.
Page 5 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
6
RESULTS
Hearing Thresholds
The audiometric examinations of jet pilots from a German airline company are presented as
average audiograms in age-groups, hereby evaluating both ears and the averaged differences
between both ears. In Fig. 1a the averaged thresholds of all pilots in the age groups and both
ears are presented in the upper part and the left-right differences in the lower part Fig 1b. The
results are two completely separated curves clearly indicating better hearing for younger
pilots. At low frequencies up to 1.5 kHz the curves are parallel with differences between 2
and 4 dB. From 2 kHz up to 14 kHz the differences increase up to about 30 dB. The 16 kHz
value in the older group is distorted by missing data caused by the limitations of the
audiometer. Fig. 1b shows small threshold differences < ± 1 dB between both ears up to 2
kHz. Here both curves cross the zero level from “right ear worse” to “left ear worse” with
increasing values. The curve of the younger pilots does not exceed levels over ± 2 dB. In the
older pilots the threshold difference increases up to 6 dB at 6 kHz. The 8 kHz value seems to
be a local minimum in both age groups. In the extended frequency range the differences
between right and left ear decreases and approach each other at 16 kHz at about 1 dB.
{Fig. 1}
Tab. 1: Distribution of hearing levels averaged across left and right ears (dB HL) in four age-
groups.
Frequency Centile Age (years)
20–29 30–39 40–49 50–59
3 kHz 10 -5.0 -2.5 0.0 2.5
25 0.0 0.0 2.5 7.5
Median 0.0 2.5 7.5 11.3
75 5.0 5.0 12.5 17.5
90 10.0 10.0 20 25.8
4 kHz 10 0.0 0.0 3.3 7.5
25 0.0 2.5 7.5 12.5
Median 5.0 5.0 12.5 17.5
75 10.0 10.0 19.4 26.9
90 17.5 15.0 27.5 35.0
6 kHz 10 0.0 0.0 5.0 7.5
25 5.0 5.0 10.0 12.5
Median 10.0 7.5 13.8 21.3
75 15.0 12.5 22.5 29.4
90 20.0 17.5 35.0 37.5
N 74 197 133 77
In Tab. 1 the statistical distribution in the frequencies 3, 4 and 6 kHz is presented in four age-groups
with a span of ten years. 6 pilots are between 60 and 63 years old and not considered in the
distribution.
Page 6 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
7
Age-corrected thresholds
The effect of two different age corrections can be seen in Fig. 2. The 2nd edition of ISO 7029
[8] is presented in Fig. 2a and the 3rd draft edition in Fig. 2b. Frequency range is limited to
125 Hz up to 12.5 kHz the highest correction proposal in the 3rd draft edition.
{Fig. 2}
Altogether the new version of the ISO 7029 indicates a smaller influence of aging on hearing
thresholds, especially in the frequency range from 3 to 6 kHz where the influence of noise
(ISO 1999) is most pronounced. The threshold levels of the younger pilots differed only a
little (≤ 2 dB) while in the older pilots the thresholds increased to 3.5 dB at 4 kHz, 6 dB at 4
kHz, 5 dB at 6 kHz and 7 dB at 8 kHz. The better hearing in older pilots in Fig. 2a shifts to a
worse hearing in Fig. 2b by different age correcting factors according to ISO 7029 [8].
Page 7 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
8
Cockpit Noise and Communication Sound
For nine jet models of a German airline, free field noise measurements were carried out in
the cockpit (Hoffmann 2004) [10], which were supplemented by acoustic manikin
measurements. The free-field measurements yielded values between 74 dB(A) for the B767
and 80 dB(A) for B747 jets. The sound pressure levels for communication are higher than
the ambient noise for a clear understanding of the messages. These sound pressure levels
were measured with an acoustic manikin under the headset to estimate effects on hearing. In
Tab. 2 these measurement data are presented with measurement times and the time portion
with communication (ATC) in minutes. In contrast to the uniformly ambient noise the
communication signal fluctuates and contains impulsive parts of sound. Therefore the
measurements with time constant “fast” (125 ms) were supplemented by measurements with
the time constant “impulse” (attack time 35 ms, release time 1.5 sec.).
Tab. 2: Sound pressure level measurements in 9 different jet cockpits. Free field ambient
noise (AN) measurement data during flight time are presented as well as data from an acoustic
manikin (AM). Measurement data from Hoffmann [10]. AMcATC are calculated values by
using the ISO 11904-2 [11] and the ATC time.
Jet Data Sound Pressure Data
Type Flight time ATC time ANFt AMfFt AMiFt AMcATC SNR
minutes minutes dB(A)f dB(A)f dB(A)i dB(A)f dB(A)
A310-200 162 70 74.9 81.9 87.9 83.5 8.6
A310-300 460 208 76.7 86.7 92.7 88.1 11.4
B737-200 221 81 76.8 81.4 87.4 83.8 7.0
B737-300 137 28 77.3 80.9 85.9 85.8 8.5
B747 1144 344 79.9 84.8 89.9 88.0 8.1
B757 357 134 75.1 83.7 89.9 86.0 10.9
B767 294 112 74.4 81.6 87.9 83.8 9.4
DC10 116 50 76.8 85.9 91.2 87.6 10.8
MD11 153 73 75.0 84.6 90.3 85.8 10.8
ATC(air trafic control), Ft(Flight time), AN(free field ambient noise), AM(acoustic manikin), SNR(signal to noise ratio)
dB(A)f(sound pressure level with A-weighting and time constant: fast), dB(A)i(with time constant: impulse)
AMcATC (spectral corrected values of AMfFt by ISO 11904-2 and calculated to the ATC time).
The differences between „impulse“and „fast“ measurements with the acoustic manikin
(AMiFt – AMfFt) are between 5 and 6 dB indicating an impulsive character of the
communication sound. With the time period of air traffic control (ATC) compared to the
total flight time the equivalent sound exposure of the pilots during communication can be
estimated after a spectral correction according to ISO 11904-2 [11]. This was done in the
column AMcATC. The difference between AMcATC and the ambient noise (ANFt) is the
signal to noise ratio (SNR) for communication. This value varies between minimal 7 dB and
maximal 11 dB. The average is about 10 dB.
The free field measured ambient noise in Airline cockpits does not reach the lower exposure
action values of 80 dB(A) of the EU DIRECTIVE 2003/10/EC [7] if the flight time is below
8 hours. The corrected sound pressure levels of communication sound AMc(ATC) exceeds the
Page 8 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
9
upper exposure action value of the directive of 85 dB(A) in 6 cases for a flight times of 8
hours and more. The minimum communication sound level was calculated to 83.5 dB(A) in
the Airbus A320-200, and the maximum level to 88.1 dB(A) in the Airbus A310-300. Only
in intercontinental flights the flight time reaches or exceeds 8 hours.
Statistics
With a multi-factorial ANOVA with repeated measures, the left-right differences in the
threshold data were statistically evaluated for possible influencing factors (see Tab. 3). In
addition to the age group, four other dichotomous factors were selected, which suggests an
impact on the development of noise-induced hearing deteriorations: acoustic shocks, military
service, attending discos, and the use of hearing protectors at noisy leisure activities. The
usage of the headset for communication has three options: right ear, left ear or both ears.
Tab. 3: Statistical analysis. ANOVA concerning threshold differences (left – right) with 6
between groups factors: age group, acoustic shocks, military service, disco visits, use of ear
protectors and use of the communication headset. One within groups factor is the frequency.
Analyzed were 3, 4 and 6 kHz, which are predominantly affected by noise.
between groups df F p
AgeGrp 1 8.711 0.003
AcousticShock 1 1.838 0.160
Military 1 0.142 0.707
Disco 1 0.672 0.413
EarProt 1 1.654 0.199
HeadsetEar 2 8.685 <0.001
within groups
Frequency 2 5.473 0.020
Frequency * AgeGrp 2 6.111 0.014
Significant factors and interactions (*) are expressed bold
The factor age group shows significant increasing differences between both ears and the factor
headset ear shows a significant effect (p<0.001) on the worse hearing of the left ear.
The within-subjects factor contains the three frequencies 3, 4 and 6 kHz, which have the
strongest effect of noise according to ISO 1999 [9] and is significant at p=0.02. Only 2-way
interactions between frequency and the other main factors were determined. With the exception
of “frequency x age group” all interactions are not significant and are not listed in Tab. 3.
Page 9 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
10
Headset
The dominant part of noise exposures results from communication sound as seen in Tab. 2.
More than half of the pilots (N=276) use the headset on both ears, while the others prefer to
use only one ear for radio communication.
{Fig. 3}
The preferred headset usage in the age groups is presented in Fig. 3. More than half of the
pilots (57 %) used both ears for radio communications. About a third (34 %) preferred to use
only the right ear and 9 % only the left ear. The pilots with left ear preference were all
captains sitting on the left seat with the right ear free for normal cockpit communication. 43
of these captains were older than 40 years and only 2 of them younger.
{Fig. 4}
In Fig. 4 the effects of this different behavior on the threshold differences between the ears is
presented. Between pilots with the headset on both ears and the right ear the curves are close
together. Only at 4 kHz the difference exceeds 1 dB in the standard frequency range up to 8
kHz. The pilots who prefer to use the left ear for communication tasks, show a conspicuous
worse hearing at the left ear in the analyzed frequencies with more than 7 dB at 6 kHz. At 8
kHz the effect is noticeably smaller and increases in the extended high range between 9 and
11 kHz. The 12.5 kHz threshold difference decreases to a value of about 3 dB.
Page 10 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
11
DISCUSSION
As expected, the age of the pilots is the main influence factor on the hearing ability. Fig. 1a
shows a clear separation of the two age group curves. At frequencies above 2 kHz the age
dependent differences increase. The course at 14 and 16 kHz is affected by lack of
measurements in older pilots by the limited sound pressure level of the audiometer at these
frequencies. The threshold differences between left and right ear (Fig. 1b) show a clear
tendency to worse hearing of the left ear. This tendency is most pronounced at frequencies 3 –
6 kHz and 9 – 11 kHz in both age groups and much stronger in the older pilots. At lower
frequencies (< 3 kHz) the difference values oscillate around the zero line within a ± 1 dB
range. At 1 kHz both age groups show better hearing by 1 dB of the left ear and no
dependence on age.
Age adjustment in accordance with ISO 7029 [8] should eliminate the age-related effects
from the data. The Fig. 2 shows the results of two versions of ISO 7029 [8]. The second edition
in Fig. 2a from 2000 shows a stronger dependence of the age than the new draft edition in
Fig. 2b from 2014. In the case of our dataset we get reverse results in the interesting frequency
range 3 – 6 kHz. Age corrected with the second edition the older pilots hear better and a
positive influence of the noise situation would be concluded. With the third edition the younger
pilots hear better and we recognize hearing loss. While the third edition represents a draft and
the second edition is still valid we recognize the closer outcomes of our study with the new
ISO 7029 [8] version.
In Tab. 1 the distribution of threshold measurements are presented. Compared to the
screened dataset of Engdahl et al.[12] the percentiles of our data are lower on an average of
4.5 dB and the 80 % span in our dataset is smaller on an average of 9 dB.
The free-field sound data of Hoffmann [10] in Tab. 2 in aircraft cockpits show sound
pressure levels between 74 dB(A) and 80 dB(A). Lindgren et al[1] published lower values
between 71 dB(A) and 76 dB(A). Begault [13] described higher values between 75 dB(A) for
the Airbus A 310 and 84 dB(A) for the Boeing B 727. The ambient noise in cockpits reported
by Lower and Bagshaw [14] had levels between 71 and 79 dB(A). The values of Hoffmann
[10] are in between this measurement data sets from literature. None of the free field sound
pressure levels of the ambient noise reach the upper exposure action value of 85 dB(A). If we
take into account, that noise with impulsive character is more harmful than pure continuous
noise, for noise exposure levels by communication the “impulse” weighted exposure levels
could be used. In all cases the upper exposure action values then would be reached during
communication. As the ATC time is mostly shorter than half of the total flight time and
never 8 hours, the higher exposure levels will be compensated approximately by the shorter
exposure time. The equivalent exposure levels of our pilots are than around the upper
exposure action value of 85 dB(A) in 8 hours.
Gassaway[15] has identified significantly higher values in cockpits of propeller aircraft from
an average of 95 dB(A) and strongly recommended the use of hearing protection. Military
aircraft are usually even louder. Overall, these measurements are not directly comparable,
since the measured aircraft are not the same and certainly also vary in the cockpit design and
the measurement setup.
Page 11 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
12
The noise exposure level caused by the radio communication exceeds the ambient cockpit
noise, because the messages have to be understood completely. In tests for speech-in-noise
recognition mostly a 50 % criterion is used to determine the normal skill [16]. At sound
pressure levels of 83 dB SPL Killion et al. [17] found a word recognition score of 50 % at a
corresponding signal-to-noise ratio of about 2 dB. Pilots need full understanding of the
messages at much higher SNR values. The largely standardized communication in aviation
has a high redundancy in the transferred messages, which reduces the required SNRs. In the
current study the average SNR used by the pilots was at 10 dB, obviously enough for a
recognition rate of about 100 %. Lower and Bagshaw [14] measured spectral corrected sound
levels for communication between 80 and 88 dB(A). Compared with the corresponding
ambient noise levels SNR values between 6 and 13 dB(A) can be calculated with an average
of about 10 dB(A) like in our dataset.
Circum-aural headsets with passive sound attenuation can be helpful to reduce the
communication sound levels, but they impede the communication between the crew as the
attenuation at high frequencies is much better than at low frequencies in those earphones.
Headsets with active noise reduction (ANR) systems are now commonly installed, which
reduces predominantly the masking low- frequency noise of the cockpit [18, 19]. The sound
pressure level of the radio-communication can substantially be reduced to a level below the
lower exposure action value of 80 dB(A). The pilots of the current study did not use any
hearing protection systems. The protective effect depends on wearing the headset on both
ears. Open headsets with low frequency noise reduction may allow communication between
captain and flight officer as the masking effects are reduced.
211 of the 487 pilots had a preference to use the communications headset mostly on only one
ear. This subgroup is suited to analyze the effect of radio communication on hearing. 166
pilots preferred the right ear, 45 pilots the left ear and 276 used both ears. Fig. 4 shows
significant differences between these groups. The differences between pilots who use both ears
and predominantly the right ear for communication are quite small (max. at 4 kHz 1.3 dB). The
left ear, however, shows significant greater differences with more than 7 dB at 6 kHz. In
Tab. 1 this fact can be seen as the strongest effect of the ANOVA for headset usage with
p < 0.001. With the exception of two pilots all of these pilots are in the older age group. This
asymmetry can be recognized in Fig. 1b in the older age group to a lesser degree as in Fig. 4
where the subgroup with left ear preference is particularly striking.
The right ear seems to be more resistant against the effects of noise than the left ear, because
the pilots with headset at the right ear almost do not differ significantly from those with
headset at both ears. Left-right ear threshold asymmetries are described by Pirilä et al. [3]. In
the frequency range between 3 and 6 kHz these authors found higher thresholds on the left
ear and concluded a greater susceptibility to noise induced hearing loss of the left ear as a
biological effect. Influences like handedness and the audiometric test procedure with
learning and fatigue effects could be excluded [20, 21, 22]. This effect was also present in
females to a lesser degree, because they are in general less exposed to noise. The higher left-
right differences in Cruickshanks et al. [4] may result from not excluding the users of
firearms from their dataset.
The pilot group who used both ears for communication tasks show no increased damaging
Page 12 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
13
effect at the left ear, although both ears had the same sound exposure level. A possible
explanation of this result could be the advantage of the binaural hearing [23] with the
squelch-effect (summation of interesting sound and unmasking of the noise) what leads to
reduced communication sound levels at a given ambient noise.
Based on the present findings, it can be concluded that the pilots of civil aviation have a good
hearing ability compared to other industrial workers with comparable noise exposure levels.
The left ear shows markedly higher risk of hearing damage than the right ear. If this effect is
age dependent, it cannot clearly be answered with the current dataset based on the cross-
sectional design of the study without the development of hearing loss in the individuals. The
use of headsets with active or passive noise reduction at both ears can solve this last problem
and may eliminate any risk for hearing loss in pilots during their normal occupational activity.
It may also be helpful to advise pilots to use both ears for communication over headset.
Page 13 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
14
Acknowledgements
The authors thank Gerald Fleischer for his ideas and suggestions as well as the management
of data collection in the Lufthansa service center in Frankfurt/Main. Also many thanks to
Knut Hoffmann of Lufthansa Technik in Hamburg for the measurement data in jet cockpits.
Conflict of interest declaration
The authors declare no conflict of interest.
Data sharing statement
No additional data available.
Funding statement
No funding.
Ethics statement
The data collection in this non-interventional study was part of the annual health
check-up’s within the German occupational safety and health system (health check
for pilots enforced by law). As individuals participated voluntarily in the study and all
data were analyzed anonymously, no ethical approval was required, in accordance
with German guidelines.
Contributorship statement
Conception and design: Reinhard Müller and Joachim Schneider
Administrative support: Reinhard Müller
Provision of study materials and patients: Reinhard Müller
Collection and assembly of data: Reinhard Müller
Data analysis and interpretation: Reinhard Müller and Joachim Schneider
Manuscript writing: Reinhard Müller and Joachim Schneider
Final approval of manuscript: Reinhard Müller and Joachim Schneider
Page 14 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
15
References
1. Lindgren T, Wieslander G, Dammström BG, Norbäck D. Hearing status among
commercial pilots in a Swedish airline company. Int J Audiol. 2008;47:515–519
2. Lie A, Skogstad M, Johannessen HA, Tynes T, Mehlum IS, Nordby KC, Engdahl B
and Tambs K. Occupational noise exposure and hearing: a systematic review. Int Arch
Occup Environ Health 2016; 89:351–372.
3. Pirilä T, Jounio-Ervasti K, Sorri M. Left-right asymmetries in hearing threshold levels
in three age groups of a random population. Audiology 1992;31:150–161.
4. Cruickshanks KJ, Wiley TL, Tweed TS, Klein BEK, Klein R, Mares-Perlman JA and
Nondahl DM. Prevalence of hearing loss in older adults in Beaver Dam, Wisconsin:
the epidemiology of hearing loss study. Am J Epidemiol. 1998;148(9):879–886.
5. ISO 389-5. Acoustics – Reference zero for the calibration of audiometric equipment
– Part 5: Reference equivalent threshold sound pressure levels for pure tones in the
frequency range 8 kHz to 16 kHz. Geneva, Switzerland: International Organization
for Standardization. 1999.
6. ISO 389-8. Acoustics – Reference zero for the calibration of audiometric equipment –
Part 8: Reference equivalent threshold sound pressure levels for pure tones and circum-
aural earphones. Geneva, Switzerland: International Organization for Standardization.
2004.
7. EU DIRECTIVE 2003/10/EC OF THE EUROPEAN PARLIAMENT AND OF
THE COUNCIL (2007)
8. ISO 7029. Acoustics – Statistical distribution of hearing thresholds as a function of age.
Geneva, Switzerland: International Organization for Standardization. 2000.
9. ISO 1999. Acoustics – Estimation of noise induced hearing loss. Geneva, Switzerland:
International Organization for Standardization. 2013.
10. Hoffmann K. Sound measurements in cockpits of civilian aircraft. 2004. Not poblished
data received as personal communication.
11. ISO 11904-2. Acoustics – Determination of sound immissions from sound sources
placed close to the ears – Part 2: Technique using a manikin. Geneva, Switzerland:
International Organization for Standardization. 2004.
12. Engdahl B, Tambs K, Borchgrevink HM, Hoffman HJ. Screened and unscreened
hearing threshold levels for an adult population: Results from the Nord-Trøndelag
Hearing Loss Study. Int J Audiol. 2005; 44:213–230
13. Begault DR, Wenzel EM. Assessment of noise exposure in commercial aircraft
cockpits (interim report). 1998; Available online at: http:/human-
factors.arcnasa.gov/publibary/Begault_1998_Noise_in_Cockpit.pdf.
14. Lower MC, Bagshaw M. Noise levels and communication on the flight decks of civil
aircraft. 25th Internoise proc. 1996.
Page 15 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
16
15. Gasaway DC. Noise levels in cockpits of aircraft during normal cruise and
considerations of auditory risk. Aviat Space Environ Med. 1986;57: 103–112.
16. Thibodeau LM. Speech Audiometry. In Roeser JR, Valente M and Hosford-Dunn
H. Audiology. 2nd Ed. Thieme, 2007. New York, Stuttgart
17. Killion MC, Niquette PA, Gudmundsen GI. Development of a quick speech- in-noise
test for measuring signal-to-noise ratio loss in normal-hearing and hearing-impared
listeners. J Acoust Soc Am. 2004;116(4):2395–2405.
18. Matschke RG. Communication and noise Speech intelligibility of aircraft pilots with
and without electronic compensation for noise. HNO. 1994;42:499–504.
19. Casali JG. Powered Electronic Augmentations in Hearing Protection Technology Circa
2010 including Active Noise Reduction, Electronically-Modulated Sound Transmission,
and Tactical Communications Devices: Review of Design, Testing, and Research.
International Journal of Acoustics and Vibration. 2010;15(4): 168–186.
20. Pirilä T, Jounio-Ervasti K, Sorri M. Hearing asymmetry among left-handed and right-
handed persons in a random population. Scand. Audiol. 1991;20:223–226.
21. Axelsson A, Jerson T, Lindberg U, Lindgren F. Early noise-induced hearing loss in
teenaged boys. Scand. Audiol. 1981;10:91–96.
22. Borod J, Obner L, Albert M, Stiefel S. Lateralization for pure tone perception as a
function of age and sex. Cortex 1983;19:281–285.
23. Arsenault MD, Punch JL. Nonsense-syllable recognition in noise using monaural and
binaural listening strategies. J Acoust Soc Am. 1999;105(3):1821–1830.
Figures
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears
averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal
hearing levels (dB HL). Part b shows the differences between left and right ear in dB.
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are
age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3
rd
draft (lower part b)
Fig. 3: Age groups and preferred headset usage.
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred
headset usage from 125 Hz up to 12.5 kHz.
Page 16 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 1: Part a shows hearing thresholds of civilian airline pilots in two age groups at both ears averaged from 125 Hz up to 16 kHz. Values are relative to standard ISO 389 [5, 6] normal hearing levels (dB HL). Part b
shows the differences between left and right ear in dB.
Page 17 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 2: Hearing thresholds of civilian airline pilots in two age groups at both ears. Values are age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3rd draft (lower part b)
Page 18 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 3: Age groups and preferred headset usage.
Page 19 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
Fig. 4: Averaged threshold differences (left ear – right ear) according to the preferred headset usage from 125 Hz up to 12.5 kHz.
130x72mm (300 x 300 DPI)
Page 20 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
1
Statement—Checklist
Item
No Recommendation
On
Page
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 1
(b) Provide in the abstract an informative and balanced summary of what was done
and what was found
2
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 3
Objectives 3 State specific objectives, including any prespecified hypotheses 3
Methods
Study design 4 Present key elements of study design early in the paper 4
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,
exposure, follow-up, and data collection
4
Participants 6 (a) Give the eligibility criteria, and the sources and methods of selection of
participants
4
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect
modifiers. Give diagnostic criteria, if applicable
-
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of
assessment (measurement). Describe comparability of assessment methods if there
is more than one group
-
Bias 9 Describe any efforts to address potential sources of bias -
Study size 10 Explain how the study size was arrived at 4
Quantitative
variables
11 Explain how quantitative variables were handled in the analyses. If applicable,
describe which groupings were chosen and why
-
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 5
(b) Describe any methods used to examine subgroups and interactions 9
(c) Explain how missing data were addressed -
(d) If applicable, describe analytical methods taking account of sampling strategy -
(e) Describe any sensitivity analyses -
Results
Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially
eligible, examined for eligibility, confirmed eligible, included in the study,
completing follow-up, and analysed
4, 10
(b) Give reasons for non-participation at each stage 4
(c) Consider use of a flow diagram -
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and
information on exposures and potential confounders
-
(b) Indicate number of participants with missing data for each variable of interest -
Outcome data 15* Report numbers of outcome events or summary measures -
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and
their precision (eg, 95% confidence interval). Make clear which confounders
were adjusted for and why they were included
-
(b) Report category boundaries when continuous variables were categorized -
(c) If relevant, consider translating estimates of relative risk into absolute risk for a
meaningful time period
-
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and
sensitivity analyses
-
Page 21 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from
For peer review only
2
Discussion
Key results 18 Summarise key results with reference to study objectives
Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or
imprecision. Discuss both direction and magnitude of any potential bias
11
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,
multiplicity of analyses, results from similar studies, and other relevant evidence
12
Generalisability 21 Discuss the generalisability (external validity) of the study results 13
Other information
Funding 22 Give the source of funding and the role of the funders for the present study and, if
applicable, for the original study on which the present article is based
-
*Give information separately for exposed and unexposed groups.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published
examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the
Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and
Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
Page 22 of 22
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on May 2, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-012913 on 30 M
ay 2017. Dow
nloaded from