Noise exposure and auditory thresholds of German airline ...€¦ · Germany Fon: +49 641 9941316 Fax: +49 641 9941319 Mail: [email protected] Keywords:

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

http://bmjopen.bmj.com/


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


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



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 20 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



Noise exposure and auditory thresholds of civilian airline

pilots. A cross sectional study. (Revised version)

Journal: BMJ Open

Manuscript ID bmjopen-2016-012913.R1


Date Submitted by the Author: 19-Sep-2016








BMJ Open on M


http://bmjopen.bm

j.com/

BM


jopen-2016-012913 on 30 May 2017. D

ownloaded from



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




IPAS Akustiklabor


Aulweg 123

35392 Giessen

Germany

Fon: +49 641 9941316

Fax: +49 641 9941319


Keywords:


noise ratio


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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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.








Page 2 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



4

METHODS

Study Population


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






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


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).


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).




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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



5

Age-correction


widely in age. To analyze other factors it is useful to eliminate the factor age from the




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.




factorial ANOVA with repeated measures was calculated using SPSS 20.

Page 5 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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}


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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



7


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




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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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




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.


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


headset ear shows a significant effect at p<0.001 on the worse hearing of the left ear.


strongest effect of noise according to ISO 1999 [9] and is significant at p=0.02. Only 2-way


of “frequency x age group” all interactions are not significant and are not listed in Tab. 3.

Headset



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



10

only the right ear and 9 % only the left ear. The pilots with left ear preference were all


of these captains were older than 40 years and only 2 of them younger.

{Fig. 4}







11 kHz. The 12.5 kHz threshold difference is similar to 8 kHz less affected.

Page 10 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



11

DISCUSSION








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.


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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



12


noise, because the messages have to be understood completely. In tests for speech in noise



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






Tab. 1 this fact can be seen in the strongest effect of the ANOVA for headset usage with


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.



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




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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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.




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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



14

Acknowledgements


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.





Funding statement

No funding.

Ethics statement


personal questions answered pilots voluntarily with consent to publish the data anonymously.









Page 14 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



15

References



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.



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.








2004.


THE COUNCIL (2007)



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:








14. Lower MC, Bagshaw M. Noise levels and communication on the flight decks of civil

aircraft. 25th Internoise proc. 1996.

Page 15 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



16






















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.


age corrected according to standard ISO 7029 [8] in two editions: 2nd (upper part a) and 3

rd

draft (lower part b)




Page 16 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 19 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




130x72mm (300 x 300 DPI)

Page 20 of 20


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



Noise exposure and auditory thresholds of German airline


Journal: BMJ Open



Date Submitted by the Author: 22-Nov-2016








BMJ Open on M


http://bmjopen.bm

j.com/

BM


jopen-2016-012913 on 30 May 2017. D

ownloaded from



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




IPAS Akustiklabor


Aulweg 123

35392 Giessen

Germany

Fon: +49 641 9941316

Fax: +49 641 9941319


Keywords:


noise ratio


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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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



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.


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 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.








Page 2 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



4

METHODS

Study Population





questionnaires were lost or incomplete. Further 12 people were excluded, because they did














room of the medical center of the airline company. The audiometer was a type CA540 from







Nüß (Hamburg).





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



Page 4 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



5

Age-correction


widely in age. To analyze other factors it is advisable to eliminate the age factor from the






the decision of which version is used and become arbitrary. In the current study we will








Page 5 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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}


groups.


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



distribution.

Page 6 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



7



[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}







Page 7 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



8




















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





(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.


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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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.


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.



AgeGrp 1 8.711 0.003


Military 1 0.142 0.707

Disco 1 0.672 0.413

EarProt 1 1.654 0.199


within groups

Frequency 2 5.473 0.020




headset ear shows a significant effect (p<0.001) on the worse hearing of the left ear.





Page 9 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



10

Headset




{Fig. 3}






{Fig. 4}







11 kHz. The 12.5 kHz threshold difference decreases to a value of about 3 dB.

Page 10 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



11

DISCUSSION










dependence on age.





















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.






Page 11 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



12


noise, because the messages have to be understood completely. In tests for speech-in-noise



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.



attenuation at high frequencies is much better than at low frequencies in those earphones.


reduces predominantly the masking low- frequency noise of the cockpit [18, 19]. The sound



hearing protection systems. The protective effect depends on wearing the headset on both



211 of the 487 pilots had a preference to use the communications headset mostly on only one






Tab. 1 this fact can be seen as the strongest effect of the ANOVA for headset usage with



where the subgroup with left ear preference is particularly striking.




the frequency range between 3 and 6 kHz these authors found higher thresholds on the left




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.


Page 12 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



13












Page 13 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



14

Acknowledgements








Funding statement

No funding.

Ethics statement


personal questions answered pilots voluntarily with consent to publish the data anonymously.









Page 14 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



15

References


















2004.


THE COUNCIL (2007)


















Page 15 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



16






















Figures






rd





Page 16 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from





Page 17 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 18 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 19 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




130x72mm (300 x 300 DPI)

Page 20 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from





Journal: BMJ Open



Date Submitted by the Author: 25-Jan-2017








BMJ Open on M


http://bmjopen.bm

j.com/

BM


jopen-2016-012913 on 30 May 2017. D

ownloaded from






2





IPAS Akustiklabor


Aulweg 123

35392 Giessen

Germany

Fon: +49 641 9941316

Fax: +49 641 9941319


Keywords:


noise ratio




high sound levels of communication with headsets to which the left is more susceptible to

damage.

Page 1 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



2

ABSTRACT









dB(A) and 88 dB(A).









exposure levels under the headset are between 7 and 11 dB(A) higher than the ambient



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.








Page 2 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



3

INTRODUCTION






hearing test at the annual health check-ups is mandatory. Nevertheless, sound exposure for











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.






Page 3 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



4

METHODS

Study Population





questionnaires were lost or incomplete. Further 12 people were excluded, because they did





















Nüß (Hamburg).








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



Page 4 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



5

Age-correction
















Page 5 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



6

RESULTS

Hearing Thresholds















{Fig. 1}


groups.


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



distribution.

Page 6 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



7





{Fig. 2}







Page 7 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



8




















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





(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.




Page 8 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



9





Statistics




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.






AgeGrp 1 8.711 0.003


Military 1 0.142 0.707

Disco 1 0.672 0.413

EarProt 1 1.654 0.199


within groups

Frequency 2 5.473 0.020









Page 9 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



10

Headset




{Fig. 3}






{Fig. 4}








Page 10 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



11

DISCUSSION










dependence on age.





















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.






Page 11 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



12







has a high redundancy in the transferred messages, what reduces the required SNRs. In the





































Page 12 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



13












Page 13 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



14

Acknowledgements








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.









Page 14 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



15

References


















2004.


THE COUNCIL (2007)


















Page 15 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



16






















Figures






rd





Page 16 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from





Page 17 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 18 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 19 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




130x72mm (300 x 300 DPI)

Page 20 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



1


Item

No Recommendation

On

Page



and what was found

2

Introduction



Methods




4


participants

4



-

Data sources/

measurement




-



Quantitative

variables



-






Results




4, 10





-






-




-



-

Page 21 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



2

Discussion




11



12


Other information



-






Page 22 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from





Journal: BMJ Open



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




Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, Audiology < OTOLARYNGOLOGY, Noise and Health


BMJ Open on M


http://bmjopen.bm

j.com/

BM


jopen-2016-012913 on 30 May 2017. D

ownloaded from






2





IPAS Akustiklabor


Aulweg 123

35392 Giessen

Germany

Fon: +49 641 9941316

Fax: +49 641 9941319


Keywords:


noise ratio




high sound levels of communication with headsets to which the left ear seems to be more

susceptible to damage.

Page 1 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



2

ABSTRACT









dB(A) and 88 dB(A).









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.







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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



3

INTRODUCTION






hearing test at the annual health check-up is mandatory. Nevertheless, sound exposure for











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.






Page 3 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



4

METHODS

Study Population


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).










Nüß (Hamburg).








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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



5

Age-correction
















Page 5 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



6

RESULTS

Hearing Thresholds















{Fig. 1}


groups.


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



distribution.

Page 6 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



7





{Fig. 2}







Page 7 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



8




















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





(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.




Page 8 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



9





Statistics




impact on the development of noise-induced hearing deteriorations: acoustic shocks, military








AgeGrp 1 8.711 0.003


Military 1 0.142 0.707

Disco 1 0.672 0.413

EarProt 1 1.654 0.199


within groups

Frequency 2 5.473 0.020









Page 9 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



10

Headset




{Fig. 3}






{Fig. 4}








Page 10 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



11

DISCUSSION










dependence on age.





















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.






Page 11 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



12







has a high redundancy in the transferred messages, which reduces the required SNRs. In the





































Page 12 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



13








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


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



14

Acknowledgements








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.









Page 14 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



15

References


















2004.


THE COUNCIL (2007)


















Page 15 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



16






















Figures






rd





Page 16 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from





Page 17 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 18 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




Page 19 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from




130x72mm (300 x 300 DPI)

Page 20 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



1


Item

No Recommendation

On

Page



and what was found

2

Introduction



Methods




4


participants

4



-

Data sources/

measurement




-



Quantitative

variables



-






Results




4, 10





-






-




-



-

Page 21 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from



2

Discussion




11



12


Other information



-






Page 22 of 22


BMJ Open

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960



jopen.bmj.com

/B

MJ O


ay 2017. Dow

nloaded from


Documents

Noise exposure and auditory thresholds of German airline ...€¦ · Germany Fon: +49 641 9941316 Fax: +49 641 9941319 Mail: [email protected] Keywords: