Radio speech communication and workload in military

Radio speech communication and workload in military
D 1398
OULU 2016
UNIVERSITY OF OUL U P.O. Box 8000 FI-90014 UNIVERSITY OF OULU FINLA ND
U N I V E R S I TAT I S
O U L U E N S I S
ACTA
A C TA
D 1398
ACTA
U N I V E R S I T AT I S O U L U E N S I S
Taija Lahtinen
University Lecturer Santeri Palviainen
Postdoctoral research fellow Sanna Taskila
Professor Olli Vuolteenaho
Taija Lahtinen
Professor Esa Hohtola
RADIO SPEECH
COMMUNICATION
AND WORKLOAD IN
MILITARY AVIATION
A HUMAN FACTORS PERSPECTIVE
University Lecturer Veli-Matti Ulvinen
Director Sinikka Eskelinen
Professor Jari Juga
University Lecturer Anu Soikkeli
Professor Olli Vuolteenaho
Publications Editor Kirsti Nurkkala
ISBN 978-952-62-1427-6 (Paperback)
ISBN 978-952-62-1428-3 (PDF)
ISSN 0355-3221 (Print)
ISSN 1796-2234 (Online)
UNIVERSITY OF OULU GRADUATE SCHOOL;
UNIVERSITY OF OULU,
FACULTY OF MEDICINE;
FINNISH DEFENCE FORCES,
CENTRE FOR MILITARY MEDICINE
D
MEDICA
ACTA UNIVERSITATIS OULUENSIS
D Medica 1398
TAIJA LAHTINEN
RADIO SPEECH COMMUNICATION
AND WORKLOAD IN MILITARY
AVIATION
A human factors perspective
Academic dissertation to be presented with the assent
of the Doctoral Training Committee of Health and
Biosciences of the University of Oulu for public defence
in Auditorium 4 of Oulu University Hospital, on 9
December 2016, at 12 noon
U N I VE R S I T Y O F O U L U , O U L U 2 0 1 6
Copyright © 2016
Acta Univ. Oul. D 1398, 2016
Supervised by
Docent Tuomo Leino
Professor Martti Sorri
Reviewed by
Professor Kai Parkkola
Docent Rauno Pääkkönen
Opponent
Docent Antti Aarnisalo
ISBN 978-952-62-1427-6 (Paperback)
ISBN 978-952-62-1428-3 (PDF)
ISSN 0355-3221 (Printed)
ISSN 1796-2234 (Online)
Cover Design
Raimo Ahonen
JUVENES PRINT
TAMPERE 2016
Lahtinen, Taija, Radio speech communication and workload in military aviation.
A human factors perspective
University of Oulu Graduate School; University of Oulu, Faculty of Medicine; Finnish Defence
Forces, Centre for Military Medicine
Acta Univ. Oul. D 1398, 2016
University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland
Abstract
Military aviation is characterised by challenging working environments. Even though flying is a
heavily visual task, much of the most important information is expressed aurally, via radio. The
purpose of this study is to investigate the characteristics of radio communication in military
aviation environments, the effect of workload on radio communication, as well as the functionality
of a new hearing protection system.
Flight simulator (F/A-18 Hornet simulator) and heart rate analysis were used to analyse the
effect of an increased workload on radio communication. In addition to this, two survey studies
were conducted, the first to investigate the prevalence and nature of radio communication
problems in military aviation environments, and the second for evaluating the functionality of a
new hearing protection solution (moulded communication ear plugs, m-CEPs) for military pilots.
In the flight simulator, pilots’ heart rate reflected the level of mental workload. Changes in
radio communication were observed during a high workload: The total amount of communication,
as well as informing and requesting messages increased. A decrease in acknowledgements was
observed. This reflects a change in the team communication tactics during information-loaded
flight phases.
In survey studies, radio speech communication problems occurred during 14% of the flight
time. The most prevalent problems included multiple speakers and overlapping speech on the
radio frequency band, missing acknowledgments, and high background noise, especially during
helicopter operations. During their career, 18% of the respondents had encountered a potentially
dangerous event caused by radio communication problems.
The pilots reported a high motivation to use enhanced hearing protection systems. m-CEPs
were shown to be a promising tool for improving hearing protection and radio communication:
they were considered to be better than the previous hearing protectors, and the pilots reported that
they improve the experienced speech intelligibility. However, discomfort and technical problems
remain a problem.
In the challenging hearing conditions of military aviation, the high quality of radio
communication and hearing protection remain important. In the future, radio communication
training should be improved and focused on team communication training. The technical
development of hearing protection devices should be continued to assure the best possible comfort
and technical reliability.
Keywords: aerospace medicine, hearing protection, heart rate, human factors, noise,
radio communication
Lahtinen, Taija, Sotilasilmailun radiopuheviestintä ja kuormitus. Inhimillisten
tekijöiden näkökulma
Oulun yliopiston tutkijakoulu; Oulun yliopisto, Lääketieteellinen tiedekunta; Puolustusvoimat,
Sotilaslääketieteen keskus
Acta Univ. Oul. D 1398, 2016
Oulun yliopisto, PL 8000, 90014 Oulun yliopisto
Tiivistelmä
Sotilaslentäjä työskentelee fyysisesti, psyykkisesti ja kognitiivisesti hyvin haastavassa monitehtäväympäristössä. Radiopuheviestinnän onnistuminen on lentoturvallisuuden ja tehtävätehokkuuden kannalta olennaista, sillä merkittävä osa turvallisuuden kannalta kriittisestä informaatiosta välitetään puheella radioteitse. Tämän väitöstutkimuksen tavoitteena on selvittää radiopuheviestinnän ongelmien esiintymistä ja luonnetta, kuormituksen vaikutusta radiopuheviestintään
sekä uuden kuulonsuojausjärjestelmän toimivuutta sotilaslentäjän työssä.
Tutkimus toteutettiin lentosimulaattorissa sekä kahdella kyselytutkimuksella. F/A-18 Hornet
-simulaattorissa tutkittiin sykeanalyysin avulla lentotehtävän psyykkisen kuormituksen vaikutusta radiopuheviestintään. Kyselytutkimuksilla selvitettiin radiopuheviestintäongelmien yleisyyttä
ja luonnetta sekä uuteen kuulonsuojausjärjestelmään (yksilöllisesti valettu kommunikaatiokuulosuojain) liittyviä tekijöitä.
Sykeanalyysi osoittautui käyttökelpoiseksi psyykkisen kuormituksen arviontiin simulaattorissa. Radiopuheviestintä muuttui kuormittavassa lentovaiheessa: viestinnän määrä lisääntyi; informoivat ja kysyvät viestit lisääntyivät; ja kuittaukset vähenivät.
Kyselytutkimuksissa lennon aikaisia radiopuheviestinnän ongelmia raportoitiin esiintyvän 14
% lentoajasta. Suuri puhujien määrä ja päällekkäinen puhe radiojaksolla, kuittausten puuttuminen sekä taustamelu varsinkin helikopteritoiminnassa olivat merkittävimpiä ongelmia. Vastaajista 18 % kertoi kohdanneensa urallaan läheltä piti- tai vaaratilanteen, johon radiopuheviestinnän
ongelma oli myötävaikuttanut.
Lentäjät olivat hyvin motivoituneita käyttämään uusia kuulonsuojausjärjestelmiä. Yksilöllisesti valetut kommunikaatiokuulosuojaimet vaikuttavat lupaavalta ratkaisulta kuulonsuojauksen
ja viestinnän parantamiseen. Lentäjät pitivät niitä parempina kuin aiemmat kuulonsuojausjärjestelmät, ja niiden raportoitiin parantavan puheen ymmärrettävyyttä sotilasilmailun haastavissa
kuunteluolosuhteissa. Mukavuusongelmia ja teknisiä ongelmia esiintyi kuitenkin edelleen runsaasti.
Sotilasilmailun haastavissa kuunteluolosuhteissa laadukas radioviestintä ja toimiva kuulonsuojaus ovat tärkeitä. Radiopuheviestinnän harjoittelussa tulisi panostaa tehtäviä suorittavien
ryhmien keskinäisen viestinnän (team communication) parantamiseen. Kuulonsuojausjärjestelmiä tulee edelleen kehittää.
Asiasanat:
ilmailulääketiede,
radiopuheviestintä, syke
inhimilliset
tekijät,
kuulonsuojaus,
melu,
Lentokenttien aavoilla tuulee
niin kuin ulapalla autiomaan,
ja kiitotien päässä on taivaassa reikä
ovi miltei mahdottomaan.
-Edu Kettunen
8
Acknowledgements
This study was carried out in the research project “PURE - Speech recognition in
demanding tasks”, in collaboration with the Department of Otorhinolaryngology,
University of Oulu and the Finnish Defence Forces (Centre for Military Medicine
and the Finnish Air Force) between years 2005-2016.
I want to express my deepest gratitude to my main supervisors, Professor
Emeritus Martti Sorri M.D., Ph.D. and Docent Tuomo Leino M.D, Ph.D. Tuomo
Leino introduced me to this project and was my primary source of help. He has an
exceptional knowledge on aerospace medicine and I am honoured to work with him.
Martti Sorri, the scientific leader of the research project, has helped me
tremendously and his expertise in audiology and a supportive attitude towards a
PhD student have been vital for this thesis. Professor Tomi Laitinen M.D., Ph.D.
helped remarkably at the beginning of this project with heart rate analysis.
I wish to warmly thank Surgeon General (ret.), Maj.Gen (M.C.) Pentti Kuronen
M.D., Ph.D., the leader of the research project for the many ways he supported this
study, and for his supportive attitude towards a young colleague. I want to thank
the coordinator of the PURE- project, Docent Kerttu Huttunen, Ph.D., for the many
ways she helped me with both theoretical and practical matters. Her professional
comments and deep knowledge of the scientific world have taught me more than
anyone can imagine. Surgeon General of the Finnish Defence Forces, Brig.Gen
(M.C.) Simo Siitonen M.D., Ph.D., was part of a follow-up group for this thesis
and his guidance and support during these years has been exceptional.
I wish to thank the official reviewers of this work, Docent Rauno Pääkkönen
D.Sc. (Tech) and Professor Kai Parkkola, M.D., Ph.D. I deeply appreciate their
important comments and supportive, professional attitude in evaluating this thesis.
Their input and comments improved this thesis remarkably.
I want to thank my co-workers Heikki Keränen M.A., Jukka Koskelo M.Sc.,
and Arto Muhli B.Sc., for your expertise and help. Capt (ret.) Taisto Puhakka
offered a great deal of help with the practical matters in this research.
I am also grateful for several persons in Oulu University Hospital, department
of Otorhinolaryngology: Administrative deputy chief physician Samuli Hannula,
M.D., Ph.D. and Professor Olli-Pekka Alho, M.D, Ph.D. for their encouraging
attitude towards my thesis, and them and several other colleagues for their help
during the time I was working at the department. The clinic secretaries Raili
Puhakka and Merja Portimo, as well as several persons in the administrative office
of Faculty of Medicine, University of Oulu have been very helpful.
9
I also want to thank several persons in the Finnish Defence Forces. I am
grateful for Col. (M.C.) Jouko Peltomaa, M.D., D.D.S., director of Centre for
Military Medicine and LtCdr (M.C.) Markku Kerola, M.D., for their support and
for creating an inspiring working environment which enables a physician to also
carry out scientific work. Research secretary Kari Kelho helped remarkably with
administrative issues. I want to thank my fellow ‘flight docs’ across the country and
abroad, and my co-workers at Rovaniemi garrison health centre. I am grateful for
all the pilots who participated in the simulator experiments and the survey studies.
I want to thank the management, flight safety officers and pilots of Lapland Air
Command for the supportive working environment for a flight surgeon. Lapland
Air Command is also thanked for the daily flight rounds over my home; watching
you makes it easy to remember why I am doing this.
What has amazed me over these past years is the incredible attitude that exists
among the people I have worked with. When I started with this research project by
doing my advanced special studies, I was a second year medical student without
any military training and with only very little experience in medicine. I wished to
join a high-class military aviation research project, and all I had to offer was some
enthusiasm. What was the response? A warm welcome from everyone, regardless
of the ranks and titles, and an unlimited support during these years. Your attitude
kept me going during the desperate moments of this work. Alongside this project,
also a medical officer, flight surgeon and a private pilot was generated – and
without the people I have had the privilege to work with, I would not be in my
dream job today. Thank you.
Finally, my warmest thank you goes to my friends and loved ones. My
medschool friends, especially Noora Kökkö and Aki Käräjämäki, because of our
skiing trips and watching-the-ER -marathons I survived my way through medical
school. Inari Summanen, Elina Hirttiö and Anna Huttunen, thank you for the many
years of friendship. Anna Rantanen, thank you for…well…a lot. I want to thank
my family; my mother Anitta Lahtinen, little brother Juha-Matti Lahtinen and all
my other relatives for everything that you are. Jori Lindroth, thanks for sticking
with a wanderer like me, you are my solid rock, and I love you.
This work was financially supported by the Centre for Military Medicine, the
Finnish Audiological Society, the Lapland Regional Fund and the Finnish Medical
Foundation, which are gratefully acknowledged.
Rovaniemi, 20. October 2016
10
Taija Lahtinen
Abbreviations
ANR
ATC
CAP
CEP
CRM
CRT
dB(A)
dB(C)
EASA
EU
FDF
FinAF
ft
F/A
Gz
HF
HFACS
HPD
HR
HRV
IATA
ICAO
ILS
JHMCS
M-CEP
NASA
NATO
NIHL
ns
OMARA
Miliears
PTS
SA
SNHL
active noise reduction
air traffic control
combat air patrol
communication ear plug
crew resource management
cathode ray tube (display type in aircraft)
sound pressure level with A-weighting
sound pressure level with C-weighting
European Aviation Safety Agency
European Union
Finnish Defence Forces
Finnish Air Force
foot; unit of length used in aviation, 1 ft = 0.3048m
Fighter and attack aircraft
G-force in z-axis (head to toe), a force acting on body due to
acceleration inertia
Human factors
Human Factors Analysis and Classification System
hearing protection device
heart rate
heart rate variability
International Air Transport Association
International Civil Aviation Organization
Instrument Landing System
Joint Helmet Mounted Cueing System
Moulded communication ear plug
National Aeronautics and Space Administration
North Atlantic Treaty Organization
Noise-induced hearing loss
Not statistically significant
A trademark for a moulded communication ear plug
A trademark for a moulded communication ear plug
Permanent threshold shift
Situation awareness
Sensorineural hearing loss
11
SNR
TTS
WTT
3D
12
Signal to noise ratio
Temporary threshold shift
Weapons tactics trainer (dome flight simulator)
Three-dimensional
List of original publications
This thesis is based on the following publications, which are referred throughout
the text by their Roman numerals:
I
Lahtinen TMM, Koskelo JP, Laitinen T, Leino TK: Heart rate and performance during
combat missions in a flight simulator. Aviat Space Environ Med 78: 387–391.
II Lahtinen TMM, Huttunen KH, Keränen HI, Sorri MJ, Leino TK: Radio speech
communication during simulated air combat missions. Manuscript.
III Lahtinen TMM, Huttunen KH, Kuronen PO, Sorri MJ, Leino TK. Radio speech
communication problems reported in a survey of military pilots. Aviat Space Environ
Med 81: 1123–1127.
IV Lahtinen TMM, Leino TK: Molded Communication Earplugs in Military Aviation.
Aerosp Med Hum Perform 86(9): 808–814.
13
14
Contents
Abstract
Tiivistelmä
Acknowledgements
9
Abbreviations
11
List of original publications
13
Contents
15
1 Introduction
19
2 Review of literature
21
2.1 Military aviation working environment, basics of flight safety
and human factors ................................................................................... 21
2.1.1 Physical working environment ..................................................... 21
2.1.2 Workload in military aviation: Performance, and
psychological and cognitive challenges of the working
environment .................................................................................. 22
2.1.3 The basics of flight safety - Human factors and human
error .............................................................................................. 30
2.1.4 Pilot workload analysing techniques ............................................ 35
2.2 Noise, hearing and hearing protection in military aviation ..................... 38
2.2.1 Characteristics of human speech .................................................. 38
2.2.2 Noise and hearing, noise-induced hearing loss and general
noise protection requirements....................................................... 39
2.2.3 Hearing requirements for military pilots ...................................... 41
2.2.4 Noise levels in military aviation ................................................... 44
2.2.5 Noise exposure times, prevalence of hearing impairment
and the need for hearing protection in military aviation............... 47
2.2.6 Other harmful effects of noise: hearing and listening in
noise, signal-to-noise ratio, noise and workload .......................... 48
2.2.7 Hearing protection solutions in military aviation ......................... 50
2.3 Radio communication in military aviation .............................................. 55
2.3.1 Basics of aviation radio communication ...................................... 55
2.3.2 Radio communication problems: some typical error types
and their consequences ................................................................. 59
2.3.3 Workload and radio communication ............................................. 62
3 Aims of this study
63
4 Subjects and methods
65
15
4.1 Subjects ................................................................................................... 65
4.1.1 Subjects in simulator studies ........................................................ 65
4.1.2 Subjects in survey studies ............................................................. 65
4.2 Flight simulator studies (I & II) .............................................................. 66
4.2.1 Flight simulator ............................................................................ 66
4.2.2 Simulated flight mission (Studies I & II), reading tasks
(Studies I & II), cognitive load analysis (Study II) ...................... 66
4.2.3 Heart rate measurements (Study I) ............................................... 69
4.2.4 Flight performance measurements (Study I) ................................ 70
4.2.5 Communication analysis (Study II) .............................................. 70
4.3 Survey studies ......................................................................................... 71
4.3.1 Radio speech communication in military aviation - survey
(Study III) ..................................................................................... 71
4.3.2 Moulded communication earplugs (m-CEP) survey (Study
IV) ................................................................................................ 72
4.4 Statistical analysis (Studies I-IV) ............................................................ 73
4.5 Ethical issues ........................................................................................... 75
5 Results and Comments
77
5.1 Studies I & II: Pilot workload, associated heart rate changes and
radio communication changes in flight simulator ................................... 77
5.1.1 Heart rate (HR) and workload issues in flight simulator
(Study I) ........................................................................................ 77
5.1.2 Radio communication during simulated flight (Study II) ............. 81
5.2 Study III: Radio speech communication problems survey ...................... 84
5.2.1 Background data ........................................................................... 84
5.2.2 Prevalence of radio speech communication problems .................. 85
5.2.3 Speech rate and speech characteristics ......................................... 87
5.2.4 Background noise ......................................................................... 89
5.2.5 Radio speech communication related incidents and
dangerous situations ..................................................................... 91
5.2.6 Comment ...................................................................................... 92
5.3 Study IV: moulded communication earplugs survey............................... 94
5.3.1 Background data ........................................................................... 94
5.3.2 m-CEPs: usage rates, positive issues, negative issues .................. 96
5.3.3 Radio communication issues in general ..................................... 100
5.3.4 Comment .................................................................................... 100
16
6 General discussion and recommendations
105
6.1 Flight simulator studies ......................................................................... 105
6.2 Survey studies ....................................................................................... 107
6.3 Reliability of the results ........................................................................ 108
6.3.1 Strengths of the study ................................................................. 108
6.3.2 Limitations of the study .............................................................. 109
6.4 Generalizability of the results ............................................................... 110
6.5 Future research and recommendations .................................................. 111
7 Conclusions; the findings of this study in the HFACS framework
115
References
119
Appendices
131
List of original publications
139
17
18
1
Introduction
Flying a fast jet fighter aircraft is one of the most demanding work assignments.
The successful completion of a military flight mission requires physical fitness,
psychological capabilities and good cognitive resources. As the aircraft systems
evolve, the limiting factor in today's military flying is pilots’ information
processing capacity: the systems of modern aircraft offer more information than is
possible to deal with. Solutions that help to reduce pilot workload can increase the
pilot’s capacity for safer and more successful flight operations.
Even though flying is a heavily visual task, much of the safety- and missioncritical information is expressed aurally, via radio. In addition, synthetic voice
alarms are used. The demanding working environment and the high background
noise levels in military aviation are a challenge for audio information delivery
channel. The high noise levels and the constant communication requirement mean
a challenge for hearing protection, and previously it has been noted that
communication in difficult hearing conditions is an important factor in operational
aerospace medicine.
More information is needed about the characteristics of radio communication
in military aviation working environments. Despite their importance, there is very
little knowledge about the prevalence and types of hearing difficulties and their
relationship with radio communication problems in military aviation. In recent
years, new methods for improving hearing protection and communication have
been introduced to everyday work in the Finnish Defence Forces, but there is only
limited data about their usability in the working environment of military pilots.
This study is part of a joint research project (University of Oulu, the Finnish
Air Force) that is aiming to understand and improve radio communication during
difficult work assignments. In this study, the characteristics of workload and radio
communication and the types of hearing and radio communication problems are
studied. In addition, new hearing protection devices and user experiences about
them are studied. The results are discussed within the human factors framework in
order to understand their relevance as flight safety factors. The focus of this study
is on the perspective of multidisciplinary human factors; technical details of the
radio systems are outside the scope of this study. The results can benefit pilots,
flight surgeons and flight instructors to better understand and prevent hearing and
radio communication problems. Better understanding of radio communication is
also beneficial in other military branches using radio communication during their
missions. Because work assignments in the field of aviation are characterised by
19
humans working in complex multitask environments, it forms an interesting
platform for studying human performance. Nowadays the findings in aerospace
medicine are also increasingly utilised in other safety-critical environments
characterised by complex tasks and people working in teams.
20
2
Review of literature
2.1
Military aviation working environment, basics of flight safety
and human factors
Military aviation is characterised by demanding working conditions. Military pilots
are exposed to stressors that are very different from ground level environmental
conditions. The workload in military aviation is a result of physical and
environmental factors and a complex combination of psychological and cognitive
issues. Even within military aviation, there is a variety in the working conditions
between different aircraft types and assignments. For fighter pilots, the challenge
is a combination of physical challenges associated with high-performance aircraft
and information-processing requirements. For transport pilots, their working
conditions resemble those of civil aviation, for example with crew resource
management (CRM) issues. For helicopter pilots, the challenges include
ergonomics, background noise, and teamwork with pilots and other helicopter crew
members.
In all military aviation, the possibility of an accident causing serious injury or
even death is present; in Finland, a total 12 pilots have lost their lives in military
aviation accidents during the last 30 years (Ilmavoimat 2016).
2.1.1 Physical working environment
The Finnish Defence Forces (FDF) currently use the Boeing F/A-18 Hornet MLU2
as a multirole fighter aircraft. The F/A-18 represents the 4th generation of fighter
aircrafts; other aircraft types belonging to this fighter generation include e.g.
Eurofighter Typhoon and Dassault Rafale (Newman 2014b). A pilot flying an F/A18 is steering a vehicle that can reach a maximum altitude of 15 000 metres and an
airspeed of 1.8 Mach, which depending on the altitude translates to approximately
2000 km/h (Ilmavoimat 2015). The pilot is exposed to rapid changes in altitude and
pressure, lower oxygen levels than at sea level, cold and heat, different light
environments, vibration, cosmic radiation and noise. During manoeuvring and
especially during air combat the pilot is exposed to high G-forces reaching +Gz
levels of 7 to 9 multiples of the Earth’s gravitational force (Newman & Callister
1999). The cockpit is small and allows very little space for movement. The duration
of the flight missions vary: they may be short (tens of minutes), but when air
21
refuelling is used, they may last for several hours. The acoustic environment is
challenging: noise levels are generally high (Kuronen 2004) including both
continuous and impulse-type noise as well as noise caused by radio communication.
Noise levels differ depending on the aircraft type, phase of flight, engine settings
and level of communication.
Several systems exist to protect the pilots from these environmental stressors,
e.g. anti-G -suits, helmets and hearing protection devices (HPD). These systems are
essential but also a potential source of stress and discomfort. For example, anti-Gsuits increase acceleration tolerance (Siitonen 2000) but reduce limb movement.
Flight helmets are essential for head and hearing protection but they also causes
strain to neck muscles, especially during high acceleration. New helmet types such
as the JHMCS (Joint Helmet-Mounted Cueing System) introduce new
opportunities for operational use, but they also include other equipment which
increase helmet weight (Lange et al. 2011).
2.1.2 Workload in military aviation: Performance, and psychological
and cognitive challenges of the working environment
To be able to complete a successful and safe flight mission, the pilot needs good
performance. Pilot performance is a wide concept and there is no single definition
for it; it may range from a very coarse scale such as whether the pilot succeeds in
safe landing or not, to refined analysis of specified performance parameters.
However, it is generally accepted that human performance is a result of several
different cognitive processes (Baker & Dismukes 2002, Lee & Liu 2003, Amalberti
et al. 2000).
Psychological and cognitive challenges and information load in military
aviation
In addition to physical challenges, military aviation working environments are
characterised by psychological and cognitive challenges. The greatest challenge is
the abundance of information (Endsley & Jones 1997, Deveans & Kewley 2009,
Newman 2014a). The systems of modern aircraft produce a massive amount of
information, which is received from visual, auditory and somatosensory routes (Liu
et al. 2012). In addition to this, the flight environment is characterised with
increasing digitalisation and automation. This all results in an increasing need to
improve the quality of information (Newman 2014a).
22
A pilot needs to handle information from both outside and inside the aircraft,
and to simultaneously control and interpret information from radar, navigation,
weapon and communications systems and from numerous different displays. This
requires the ability to perform multiple tasks simultaneously, efficiently divide
attention between subtasks and to switch rapidly from one task to another (Newman
2014a).
To give an example of the amount of information and its sources, in the F/A18 Hornet cockpit there are (Oksama & Haavisto 2006):
–
–
–
–
–
–
–
–
–
–
7 switches on the stick
19 switches on the up-front control
40 multi-function display formats
73 threat, warning, caution and advisory messages on cathode ray tube (CRT)
screens
22 head-up display formats
9 multiple function switches on the throttle
59 indicator lights
675 possible acronyms on CRT screens
177 CRT symbols
around 200 filmstrip data frames and maps on a horizontal situation multifunction display
23
Fig. 1. Cockpit of a modern fighter aircraft (F/A-18 E/F Super Hornet) (©Boeing images,
reprinted with permission.)
Stress and mental workload
The terms workload and stress have several definitions, depending on the context,
and they are sometimes misleadingly used to address the same phenomena. They
nevertheless have some differences:
Stress response as a physiological phenomenon is ‘a physiological response
that serves as a mechanism of mediation linking any given stressor to its targetorgan effect’ (Everly & Lating 2013). It is a neurochemical reaction to an
unfavourable condition that challenges the existing optimal state of the individual.
It is regulated via the autonomous nervous system and hypothalamus-anterior
pituitary-adrenal axis. A classic example of this is the fight or flight-reaction.
Individual variations in stress responses are considerable (Leino 1999).
Stress as a psychological phenomenon is ‘mental pressure’ (Oxford
Dictionaries 2016) or an ‘unfavourable condition to which an individual must adapt’
24
(Farmer 2006). The relationship between stress and performance has been
discussed since the Yerkes-Dodson law of the inverted U-shaped relationship
between arousal and performance was introduced in 1908 (Yerkes & Dodson 1908).
According to this widely recognised theory, the best performance is achieved at
moderate arousal levels, whereas at very low or very high arousal levels the
performance suffers.
Different sources of stress can be divided into the following three categories,
which together form the total stress level: (Farmer 2006)
1.
2.
3.
life stress, which is caused by stressors in the person’s life;
environmental stress which consists of factors in the external (such as physical
stressors in flight environment) and the internal environment (e.g. fatigue); and
cognitive stress, which comes from the task itself
Workload is a term that has been said to be ‘notoriously difficult to define’ (Farmer
2006). It is used for defining the requirements for a task or a mission. In dictionaries,
it is defined as ‘the amount of work to be done by someone or something’ (Oxford
Dictionaries 2016). Mental workload, according to Wickens (2002a & 2008), is a
multidimensional construct, including the level of attentional engagement and
effort that a person must expand to perform a given task. Workload has connections
to several factors in human performance. It is also related to the effort needed to
perform the task at the performance level achieved. This means that for a certain
result, different individuals require different amount of effort depending on training
and experience (Farmer 2006).
Workload components in military aviation include the following: (McCracken
& Aldrich 1984)
–
–
–
Sensory demand: complexity of visual or auditory stimuli requiring response
Cognitive demand: level of thinking required and
Psychomotor demand: the complexity of behavioural outputs required
Information load, temporal demand and communication requirements have an
effect on pilot workload. An increase in information load and/or temporal load
(‘time pressure’) during which the information needs to be dealt with, are both
associated with an increase in workload. Communication demand comes from the
continuous communication requirement between the pilot and air traffic control
(ATC), other pilots or the co-pilot and fighter controller. (Svensson & Wilson 2002,
Oksama & Haavisto 2006, Haavisto & Oksama, 2007).
25
If too many of these demands occur simultaneously or contain too much
information, the result is mental overload (Morris & Leung 2006). To cope with the
workload of a rapid-changing flight environment, the pilots need to prioritise the
subtasks of the flight mission by their urgency and/or criticality. These flight
mission subtasks are, in order of priority (Wickens 2002b):
1.
2.
3.
4.
Aviate
Navigate
Communicate
Systems management
This categorisation (ANCS) is used in pilot training. Pilots are trained to prioritise
the safe flying of the aircraft in high-workload situations. If cognitive resources
remain, as in normal situations, all these subtasks are done simultaneously.
Situation awareness (SA)
The concept of situation awareness (SA) is connected to workload in military
aviation. SA is currently stated as the basis for decision-making and action in air
combat. In fast jet environment, SA has a crucial role in the information exchange
between the pilot and the environment (Newman 2014a). The existence of SA was
understood already during the First World War: Oswald Boelke, a German military
pilot, stated ‘the importance of gaining an awareness of the enemy before the
enemy gained a similar awareness, and methods for accomplishing this’ (Gilson
1995).
Since the 1980's SA has been studied in the field of human factors (HF). Today
SA is a widely accepted concept for understanding human information processing
during complex situations. It is used especially in aviation, but also in other safetycritical fields where a human operator is functioning in a rapidly-changing
environment, such as anaesthesiology, driving and industry process control (Patrick
et al. 2006). SA can further be divided into individual SA (which addresses the SA
of a single operator) and team SA. In addition, the terms Shared SA and Distributed
SA are sometimes used for the SA of more than one operator. (Salas et al. 1995,
Stewart et al. 2008).
26
Individual situation awareness
Nowadays, the most widely used definition of individual SA, or just SA, is
Endsley’s three-level construct (Endsley 1988): Situation awareness (SA) is ’the
perception of the elements in the environment within a volume of time and space,
the comprehension of their meaning and the projection of their status in the near
future.’ (Fig.2)
SA is, therefore, three-level knowledge of the surrounding environment:
1.
2.
3.
Perception of the relevant factors
Understanding their meaning and
Projection of the unfolding situation.
Fig. 2. Model of Situation Awareness according to Endsley (reprinted with permission
of SAGE publishing)
In the military aviation context, these SA levels relate to the following practical
parameters (Endsley 1993):
–
Level 1: altitude, airspeed, location and heading of friendly and enemy aircraft;
basic flight data; location of ground threats and obstacles
27
–
–
Level 2: flight mission timing, conclusions drawn from flight data and system
status (e.g. time and distance available on remaining fuel), tactical status of air
and ground threats
Level 3: future projection of aircraft manoeuvres, projected aircraft tactics,
timing own actions and movements accordingly
The fighter pilots themselves describe good SA as (Endsley 1993):
‘Awareness of who, what, when and where of the friendlies, threats, on
ownship in the immediate tactical situation and very immediate future. It’s like
a balloon – always changing. SA is fleeting – you don’t know it’s gone until
it’s gone awhile.’
‘SA is the pilots’ perception of what he thinks is happening as opposed to what
is really happening. Only those parts which pertain to the mission are
important’.
‘What I’m doing. What they’re doing. What do you want to do to get to where
you want to be’.
Problems and errors in individual situation awareness
SA is an interpretation of the information and situation made by the operator, and
therefore it is not error-free. Because SA is the combination and a product
consisting of many human cognitive capacities, several factors that deteriorate
these capacities may also have a negative effect on SA (Newman 2014a). Errors
occur on all three levels of SA. The majority of them occur on the perception level
(level 1) of SA (Jones & Endsley 1996).
Level 1 (perception failures) form 76% of SA errors. They are failures to correctly
perceive the information (Jones & Endsley 1996). Examples include
–
–
–
information is not available (e.g. a failure in systems to present the data or
failure in the communications process);
information is not observed (e.g. not looking for information, background
noise preventing hearing, attentional narrowing);
information is misperceived or forgotten.
Level 1 SA errors occur typically during high-workload situations, where the
remembering multiple things is required. A high task load, even momentarily, may
prevent information from being attended to. If a pilot has incorrect sensory
28
information from level 1 SA, the basis of higher SA levels is erroneous and he/she
cannot form the higher SA levels correctly. In reducing level 1 SA errors, improving
the quality of information is important (Endsley 1990, Newman 2014a).
Level 2 (comprehension failures) form 20% of SA errors, making them the secondmost common type of SA errors (Jones & Endsley 1996). Level 2 errors include
situations in which the information is correctly perceived but wrongly
comprehended, for example due to a lack of a mental model or utilising an incorrect
mental model. Another example is a failure to integrate information.
Level 3 (projection failures) form only 5% of SA errors. They are failures to project
the current situation into the future (Jones & Endsley 1996).
Team situation awareness (team SA)
Complex work assignments, in aviation and other fields, are often executed in
teams. Therefore, the concept of SA has also been expanded to cover situations in
which there is more than one operator working together. A typical military aviation
team includes a pair of fighters or a fighter section and a remote-based fighter
controller(s) transmitting information to the pilots via radio and data connections.
Team SA can be defined as ‘the degree to which every team member possesses
the SA required for his or her responsibilities’ (Endsley 1995), and ‘Awareness that
each member has for his or her task responsibilities and his or her team
responsibilities’ (Prince et al. 2007).
A good team SA is characterised by the following:
–
–
–
Each team member has the knowledge necessary to conduct his or her tasks;
Each team member knows which information is known by the other team
member should he or she need to seek it;
Each team member knows which information is needed from him or her by
other team members and when (Sperling & Pritchett 2011).
In team SA, the team members need to maintain knowledge of the other team
members’ tasks and responsibilities. An important factor in team performance is to
know what is important enough to be shared with the team (Prince et al. 2007).
Maintaining team SA is not only sharing information, but also sharing the higher
levels of SA which is not directly presented on screens and displays. Most of this
sharing is done via radio communication.
29
2.1.3 The basics of flight safety - Human factors and human error
Flight safety culture is based on system thinking, human factors (HF), and
understanding the importance of human error behind accidents. Research on HF
focuses on understanding human performance within/while using systems and
devices. The goal is to enhance human performance in the workplace, especially in
complex systems (Reason 2006). Military aviation environments, such as flying a
fast jet aircraft, are a classic example of a complex working environment, requiring
HF understanding.
Human error has been known to be the most common factor behind aviation
accidents since the 1970’s both in military and civilian aviation. NASA’s Aviation
Safety Reporting System was started in 1976, and the first reports based on the data
showed that human error had occurred in over 80% of the aviation incidents
reported. The majority of these incidents included a problem in information transfer
(Billings & Reynard 1984). Although there has been a lot of progress, the same
problems remain: human error remains a causal factor in 80 to 90% of mishaps
(DoD HFACS 2015). In a study on U.S naval aviation accidents between 1990 and
1996, 75% of the accidents were associated with human factors. Of these, crew
resource management (CRM) failure was present in over half (Wiegmann &
Shappell 1999).
Human factors models
In the field of HF, several different categorisation systems and models exist for
analysing HF-related issues. Some of the most commonly used HF techniques in
the field of aviation include:
–
–
30
The SHEL-L –model. This model was developed at the beginning of the 1970s
by Edwards (Edwards 1972, as cited by Hawkins 1993) and then further
developed by Hawkins in 1975 (Hawkins 1993). The abbreviation originates
from Software – Hardware – Environment – Liveware – Liveware and it
represents the relationships between the liveware (human operator) and other
components in the system. It is used by International Civil Aviation
Organization ICAO and Eurocontrol as a basic aid to understanding HF-related
issues (ICAO 1989).
The organisational model of accident causation (the so-called ‘Swiss Cheese
model’) (Reason 1990), and the Human Factors Analysis and Classification
–
System (HFACS) based on this theory. It is used especially in the field of
military aviation. The ‘Swiss Cheese’ and HFACS models are discussed in
more detail below.
HERA (Human Error in Air Traffic Management) (Isaac et al. 2003). The
HERA system is designed to be used for analysing HF-related incidents in an
ATC environment.
‘The Swiss Cheese’ - Organisational model of accident causation
The organisational model of accident causation (‘Swiss Cheese’) is based on the
understanding that accidents and mishaps cannot usually be simplified to have been
caused by one single error. Instead, they are usually a result of multiple factors and
failures – several things that consecutively go wrong. The most known theory to
illustrate this is ‘The organizational model of accident causation’, also known as
‘The Swiss Cheese Model’ by James Reason (Reason 1990). Whereas previously,
accidents had been addressed by analysing the error immediately preceding the
accident and technical issues, the organisational accident causation model takes
system errors, latent failures and natural human fallibility on all levels into account
(Reason 1990).
Fig. 3. Swiss Cheese model, one of the human factors models used in aviation (DoD
HFACS 2015) (Reprinted with permission of the US Navy Naval Safety Center).
31
The Swiss Cheese model (Fig. 3) illustrates the chain of events leading to an
accident. The model highlights that accidents only happen if the chain of events or
errors is sufficient, and the protection mechanisms on different levels break down.
The safety of a system can be increased by making it more error tolerant by
removing holes and including protective layers. For example, the most important
flight instruments are usually doubled, which creates a protective mechanism or a
layer against an instrument failure (Reason 1990, Amalberti et al. 2000).
Human factors analysis and classification system (HFACS): Swiss
Cheese theory into practice
The Swiss Cheese model has been further utilised in accident investigation systems
and tools, among which the Human Factors Analysis and Classification System
(HFACS) is the most used, especially in military aviation settings (Shappell &
Wiegmann 2001). The purpose of HFACS is to be a framework that brings HF
theory into practice, and to be a tool for analysing the overall effect of human
factors, operations issues, engineering issues and system factors on (flight) safety.
The latest version of HFACS was released in 2015 with updates and a better
applicability to other services in addition to aviation (DoD HFACS 2015). HFACS
is presented in Figure 4.
The HFACS analyses the following factors: unsafe acts, preconditions, unsafe
supervision and organisational influences. The factors can be either causal (factors
that would have prevented or mitigated the incident, if corrected) or contributory
(not directly causal, but related to a progression of the incident).
The unsafe acts level includes the failures immediately preceding the accident.
Examples include the traditional ‘operators' errors’, such as misjudging distances,
visual and vestibular illusions, and violations or bending the existing rules.
The level above that, preconditions, includes the latent failures preceding the
final error. Preconditions include environmental factors, the condition of the
individuals and personnel factors. Examples include physical characteristics of the
working environment, physical and mental state, design of the cockpit, checklists
and teamwork issues.
The supervision level includes issues at the upper level of the organisation and
the supervisory level, such as supervisory violations, planned inappropriate
operations and inadequate supervision. Examples include situations with a lack in
supervision, a failure in risk analysis and poor planning and risk assessments.
32
The organisational influences level is the uppermost level of the system,
including resource problems, personnel selection and staffing, policy and process
issues and climate/cultural influences. These organisational issues may have a
profound effect on the entire organisation.
HFACS has been shown to be a reliable tool for analysing causes of aviation
accidents, and it is also used in other fields such as health care, logistics and
industry (Cohen et al. 2015, Diller et al. 2014, Lenné et al. 2012, Reinach & Viale
2006).
33
Fig. 4. HFACS (Human factors analysis and classification system), version 7.0 (DoD
HFACS 2015). HFACS is used for analysing human factors-related aviation safety issues
at different levels of the organisation.
34
Incident reporting
Incident reporting is another important aspect of aviation safety culture. It is based
on the understanding that minor incidents and near-misses, that did not cause a
catastrophe, should also be analysed. Accidents themselves are rare, and therefore
focusing only on accident analysis could mean that some possible risks may be
missed. For every accident that did occur, several less serious incidents with similar
features existed and could have caused an accident in some other circumstances.
This relationship between accidents, serious incidents, near misses and deviations
is stated in Heinrich's law (Fig. 5) (Ferguson & Nelson 2013). By gathering
information and analysing the less serious situations, risks can be identified and
necessary preventive actions can be taken to prevent more serious accidents
(Ferguson & Nelson 2013).
Fig. 5. Heinrich’s law. This illustrates the relationship of aviation accidents to less
serious aviation safety events (Ferguson & Nelson 2013).
2.1.4 Pilot workload analysing techniques
As described earlier, pilot workload is a combination of physical, environmental,
psychological and cognitive factors. There is no single method that could
completely measure the overall workload. Instead, numerous different workload
assessment methods exist for analysing different things. These can be divided into
the following categories: (Veltman 2002, Farmer 2006)
35
1.
Performance analysis, which can further be divided into primary and
secondary task performance analysis.
Primary task performance analysis includes e.g. analysing reaction times or
accuracy. This method is useful for simple tasks, and it is rather easy to perform.
However, measuring only primary task performance is usually not sufficient,
because two persons performing at the same level might have a significant
difference in the effort needed. In other words, the person performing the task
may increase the effort (= try harder), which causes an increase in workload
without a change in the outcome variable.
Secondary task performance analysis means that the subjects are instructed
to perform another task that is in addition to the primary task. (Farmer 2006)
2.
3.
Subjective measures, scales and questionnaires. A wide variety of subjective
scales and questionnaires exist for workload analysis in different situations.
Examples include workload questionnaires, such as NASA’s Task Load Index
(Hart & Staveland 1988). Subjective measures are widely used, because they
are generally well accepted and do not require special equipment. Their
disadvantage is that they are usually executed after the task or mission.
Therefore, the subject usually gives an overall estimate of workload, but
analysing workload changes during different phases of the task as well as
comparing different task types is difficult. A recall bias is also a possibility.
Also, if the questionnaires are executed during the missions, they cause
inevitable disruption to executing the task itself.
Physiological measures, such as heart rate (HR), heart rate variability (HRV),
neuroendocrine measures, pupil size changes and skin conductivity. The use of
physiological measures is based on the theory of increased preparedness of the
body when increased nervous activity is present. Many different physiological
measures have been used in workload analysis under laboratory conditions.
However, only some of the physiological measures (such as HR, HRV and
respiration analysis) are suitable and practical in aviation environments
(Roscoe 1992).
Physiological measures may provide objective and continuous information during
the mission, as opposed to subjective measures. The real-time nature and the
possibility to monitor them online have many benefits. For example, they could
enable noticing the excessive workload during the task. Noticing excessive
workload offers opportunities to reduce the task requirements or assist the operator.
36
The negative side of physiological measures is that they are not sensitive to any
workload type; they represent the ‘overall state of brain and body’ instead of only
task-related issues. The numerous physical factors present in a flight environment
may affect the results. There is also substantial variation in the physiological
responses between individuals, which needs to be taken into account (Veltman
2002).
Of the physiological measures, HR is the most widely used and best suited in
the field of aerospace medicine (Roscoe 1992, Roscoe 1993). In aviation context,
the following HR features have been identified:
–
–
–
–
–
HR increases with increasing job demand and in flight phases with high
workload (e.g. take-off and landing) (Opmeer & Krol 1973, Hart & Hauser
1987, Roscoe 1992, Backs 1995, Wilson 2002, Veltman 2002, Svensson &
Wilson 2002);
Increased responsibility is associated with higher HRs – captains or pilots in
charge of the flight have higher HR than co-pilots (Roman 1965, Hart & Hauser
1987);
Higher HR is associated with increased task difficulty in fighter pilots (Roscoe
1992);
HR reflects workload changes equally in real flight and in flight simulators
(Svensson & Wilson 2002, Magnusson 2002, Ylönen et al. 1997);
In a simulator, HR is able to differentiate the sub-standard flight performance
from high-standard flight (Mansikka et al. 2016).
The benefits of HR include that it is widely accepted by the pilots. It can be
measured using small devices which do not interfere with the flying task itself and
it does not require invasive procedures and laboratory analysis. Non-invasive
techniques are preferred in real-life situations, during which techniques requiring
laboratory testing and/or the storage and transportation of e.g. blood samples is
unpractical.
The disadvantages of HR analysis include that in interpreting HR results,
physical factors such as G-forces and hypoxia and strong emotions that can have
an effect on HR need to be controlled (Roscoe 1992). Also, there are major
individual differences in HR responses to mental workload (Backs 1995), but this
issue can be controlled by assessing HR against some reference level, typically an
individual’s resting HR (Blix et al. 1974, Lee & Liu 2003).
37
2.2
Noise, hearing and hearing protection in military aviation
2.2.1 Characteristics of human speech
In human speech, the sounds (or phonemes) each have a different intensity and
pitch. For hearing and understanding speech, sufficient hearing thresholds at
different frequencies is required. Vowels are pronounced at a lower pitch than
consonants, and especially unvoiced consonants (such as p, s, and t) are pronounced
at frequencies of around 4000 Hz and higher, and also with lower intensity. The
frequency characteristics of speech become important in the case of a hearing
impairment, and also in noise. Figure 6 illustrates the locations of vowels and
consonants in relation to sound pressure level and frequency. (Cranford 2008,
Arlinger 2008, Abel et al. 1982, Holma 2015).
Fig. 6. Representation of frequency characteristics of normal-volume human speech
presented in an audiogram. F0=fundamental frequency of speech, VC=voiced
consonants, V=vowels, UVC=unvoiced consonants (Holma 2015).
38
2.2.2 Noise and hearing, noise-induced hearing loss and general
noise protection requirements
Hearing impairment can be the result of several causes. High sound pressure levels
are a well-known risk factor for noise-induced hearing loss (NIHL). Other types of
hearing impairments include age-related hearing impairments, middle ear
infections and otosclerosis, hearing loss caused by ototoxic drugs and traumatic
hearing losses, to name a few (Gelfand 2009a).
High noise levels can cause three types of changes in hearing: a temporary loss
of hearing sensitivity (temporary threshold shift, TTS), permanent hearing loss
(permanent threshold shift, PTS) or, with an exposure to very high noise levels an
acoustic trauma. The onset and grade of these changes depend on several issues;
the most important of them being the noise level (sound pressure level) and the
duration of the exposure. Sound levels greater than 80dB(A) are required for these
changes; noise levels below 75dB(A) can generally be considered safe (Feuerstein
& Chasin 2009). Exposure to higher noise levels can cause TTS, which often
recovers if the noise exposure ends. If the intensity and / or duration of noise
exposure increases, it may result in PTS, although the relationship of TTS as an
indicator of PTS is ambiguous (Gelfand 2009b). The mechanism of NIHL is related
to injury in cochlear hair cells, but the effect of noise exposure is more complex
and is also caused by other changes, such as changes in the organisation of the
frequency representation in the auditory cortex (Møller 2013a).
NIHL usually begins at 4 kHz. The progression usually takes years or decades
(depending on the exposure), and with the progression this ‘4-K notch” becomes
more significant. (Gelfand 2009a & 2009b). The individual noise sensitivity differs:
e.g. genetic differences, age, smoking, solvent exposure, cardiovascular issues and
innervation of the cochlea may have an effect on noise sensitivity (Møller 2013a,
Holma 2015). Even though the first signs of NIHL often occur at 4kHz, in soldiers
(whose usual noise exposure is caused by gunfire), the first and deepest signs of
NIHL have been observed to appear at 6kHz (Holma 2015).
General noise protection requirements
To prevent work-related hearing impairment, legislation requires employers to take
preventive actions. European Union (EU) requirements define noise limits and
noise protection requirements for workers in the Noise Directive (EU 2003). In
Finnish national legislation, noise protection requirements are included in the
39
Occupational Safety and Health Act (No 738/2002) and government decrees
85/2006 and 831/2005. The noise levels and the action levels are reported in LEX,8h
meaning that the noise exposure level is normalised to an 8 hour working day. Even
though there are some restrictions in applying the Occupational Safety and Health
Act into certain parts of military work assignments, in Finland there is a desire to
follow the act and directive in the military work.
According to the EU Noise Directive, the permitted noise and action levels for
work-related noise exposure are:
–
–
–
Lower exposure action value: LEX,8h =80dB(A) or Lpeak,max =135dB(C) (when
exceeded, individual hearing protectors needs to be available to workers);
Upper exposure action value: LEX,8h =85dB(A) or Lpeak,max =137dB(C) (when
exposure is at this level or exceeded, individual hearing protection shall be
used);
Exposure limit value: LEX,8h =87dB(A) or Lpeak,max =140dB(C) (cannot be
exceeded. If this limit is exceeded, the employer shall take immediate action to
reduce the exposure to below the exposure limit values, identify the reasons
why overexposure has occurred, and amend the protection and prevention
measures in order to avoid any recurrence.)
Tinnitus and hyperacusis
Noise exposure can also cause tinnitus and/or hyperacusis. They can be defined as
hyperactive disorders of the auditory system.
Subjective tinnitus is defined as the abnormal perception of sound for which
there is no external stimulus (Gelfand 2009a, Møller 2013b, Henry et al. 2005).
Tinnitus is often (but not always) associated with hearing losses, especially the
sensorineural type. The exact prevalence of tinnitus is difficult to study. However,
it is known to be common with 6-30% of the adult population experiencing chronic
tinnitus and 1-2.5% having significant tinnitus which affects daily life (Gelfand
2009a). In a survey study among airline pilots, 18% of the respondents reported
having constant or severe tinnitus and 12% had visited a doctor because of tinnitus
(Lindgren et al. 2009). For military pilots, the figures were lower in a survey
conducted among French military pilots; of them only 0.4-1% reported frequent or
constant tinnitus, and 23% occasional tinnitus (Raynal et al. 2006).
Hyperacusis has been defined as a state when ‘moderately intense sounds are
perceived as very loud’ or as oversensitivity to sounds. The same reasons that cause
40
sensorineural hearing loss (SNHL) can also cause hyperacusis (Tyler et al. 2009,
Sjödin et al. 2012). The prevalence of hyperacusis is not well known, but among
Swedish conscripts the self-reported prevalence of sensitivity to noise was 16% at
the beginning of military service, and 19% at the end of service (Muhr & Rosenhall
2011). Among teachers the prevalence of hyperacusis without tinnitus was between
2.7-3.8% and the prevalence of hyperacusis and tinnitus together 17.3-21.2%
(Meuer & Hiller 2015). Hyperacusis is often associated with tinnitus; up to 45% of
patients suffering from tinnitus also report hyperacusis (Henry et al. 2005). No
reports about the prevalence of hyperacusis in aviation personnel could be found in
the literature.
2.2.3 Hearing requirements for military pilots
a) Authority requirements
Hearing requirements and the hearing testing intervals of pilots are defined in the
regulations by military and civilian aviation authorities. The required pure tone
hearing levels vary, depending on the flying categories and between different
countries and authorities (Fig 7). The hearing requirements are stricter for pilot
applicants than for trained pilots. If the pilot does not pass the test, authorities
usually require further investigations and speech audiometry testing and flight
proficiency tests, for example. However, in regulations no specific guidelines exist
for how to deal with those pilots who fail the pure tone tests; for example, there are
no clear limits for speech audiometry results (Hanschke 1997, ICAO 2012, United
States Air Force 2016).
41
Fig. 7. Minimum pure-tone hearing level (dB) requirements by some aviation authorities.
Sources: FinAF: Pääesikunta 2012, EASA: EU 2011 Commission Regulation (EU) No
1178/2011, Eurocontrol 2006, United States Air Force 2016, United States Navy 2010,
Royal Air Force 2016. German Armed Forces: Personal communications.
42
b) Operational requirements: auditory channel in delivering critical
information
Although flying is a heavily visual task, hearing is also important for a safe and
successful flight mission. From the operational perspective, auditory information
is often safety- and mission-critical and thus has the highest priority. Hearing
requirements include the ability to hear radio speech communication, aerodynamic
sounds, engine sound levels and changes in them, auditory warnings, synthetic
cockpit voice alarms, and to be able to communicate with other crew members,
ground staff and air traffic control (ATC) (McCracken & Aldrich 1984, Deveans &
Kewley 2009). To achieve these goals, both sufficient hearing thresholds and
speech recognition capabilities are required.
Auditory information processing, especially its higher forms such as auditory
language processing, remains an area with relatively little research, especially when
compared to visual information processing (Baldwin 2012). However, there is
evidence that using auditory information may be beneficial for performance,
especially in heavily visual environments. In situations where the main task is
visual (such as driving a car, tracking tasks and flying an aeroplane), giving
additional information aurally is advantageous for performance and time-sharing
(Wickens 2002a, Wickens & Liu 1988). In addition, auditory cues can enhance
visual performance in target aiming tasks and visual search tasks (Elias 1997).
Humans rate auditory information as important. Auditory information can
wake a person from deep sleep and high sound levels immediately grasp the
attention. Auditory information has the ability to attract attention, even when visual
attention is directed elsewhere, especially when it is presented at a sufficiently high
level (Baldwin 2011). For pilots, even though communication is ranked third in the
list of flight task priorities (aviate – navigate – communicate – systems
management), the pilots tend to interrupt other cockpit activities when auditory
information, such as radio communication, is present. This tendency to rate
auditory information highly on the list of priorities is important, but it also can have
a negative impact if it interrupts tasks higher on the priority list. However, it can be
used as an advantage when critical information needs to be delivered. This is
utilised in auditory alerts and warning systems, and also in radio communication
(Morris & Leung 2006, Wickens 2002a).
43
2.2.4 Noise levels in military aviation
Noise levels that military pilots are exposed to are high, and in the future, the noise
levels in fast jet aircrafts will increase further (Rood 1997, James 2005). Both
continuous and impulse-type noise occurs and there are differences between
aircraft types. Continuous sound pressure levels can reach 95-105dB in military
aircraft cockpits, helicopters being the noisiest (Finnish Institute of Occupational
Health 2013, Abel & Odell 2006). In the future, noise levels may be even higher
because the next-generation high-performance aircraft engines are expected to
produce noise levels of up to 110-150dB (Rajguru 2013). For example, the F35B
fighter, which is estimated to be in operative use in 2018, may have noise levels as
high as 120dB inside the cockpit during a vertical landing (James 2005). The
highest noise levels in current fighter aircraft cockpits reach 100-105 dB at
frequencies of around 500-1000 Hz. According to Rood and James (2006b), an
example of typical cabin noise spectrum inside a fast jet aircraft is presented in the
Figure 8.
Fig. 8. Typical cabin noise spectrum for a fast jet aircraft flying at high speed (450 knots
or 833km/h) at low altitude (250ft or 76m) (Rood & James 2006b).
The sources of noise in fixed-wing aircraft include engine noise (which differs
depending on aircraft settings), aerodynamic noise (which is the result of the flow
of air over aircraft surfaces and is higher at low altitudes where the air is thicker,
Fig.9), transmission systems, cockpit ventilation system, and noise from radio
44
communications. Also, pilots may be exposed to noise from other aircraft when
walking on the airfield during pre-flight inspections. In addition to these, launching
the aircraft missiles, gunfire and formation flying with several aircraft in close
proximity are other possible sources of noise (Lindgren et al. 2009, Rood & James
2006b, Kuronen 2004, Rajguru 2013).
Fig. 9. Example of the effect of altitude on noise levels inside a fast jet aircraft cabin.
(Rood & James 2006b)
Helicopter noise differs from the noise in fixed-wing aircraft. The frequency of
helicopter noise (and propeller aircraft) depends on the number of rotor blades and
their rotation speed. Helicopter noise is the highest at low frequencies, peak noise
levels being up to 110-125 dB at frequencies of around 20Hz. The noise sources in
helicopters include aerodynamic noise caused by main and tail rotors,
transmissions and gears (Fig.10).
45
Fig. 10. Cabin noise spectrum of a helicopter with a single rotor (Rood & James 2006b,
reprinted with permission).
Noise exposure caused by radio communications
Radio communications form a significant part of the aircrew’s total noise exposure.
At high noise levels, the pilots need to keep the communications volume high to be
able to hear the messages. The amount of communication obviously vary,
depending on mission types, but it can be very high. For example, in a study by
Steiman (2015) investigating noise levels in an NH90 helicopter, radio
communications were present during 90% of the mission time. Noise levels inside
the cockpit of the helicopter varied between 90 and 99 dB(A), and between 84 and
103 dB(A) in the cabin. The communications added between 3 and 17 dB(A) to
these levels, depending on the user (Steinman 2015). In another study,
communication caused an increase of 4-10 dB to the noise levels measured inside
the flight helmet (Pääkkönen & Kuronen 1998).
46
2.2.5 Noise exposure times, prevalence of hearing impairment and
the need for hearing protection in military aviation
Pilots are not in the highest risk group for hearing impairment when compared to
other military occupations (Holma 2015). Finnish military pilots have earlier been
shown to have good hearing levels (Kuronen et al. 2004a). Combat arms
occupations such as infantry and artillery have the highest prevalence of elevated
left ear hearing thresholds at 4kHz in a study by Barney & Bohnker (2006). In a
recent study in Finnish professional soldiers, the service branch groups with the
highest occurrence of NIHL were infantry, air defence and engineers (Holma 2015).
In another study among military personnel, at the age of 35-39, almost 20% had a
hearing threshold higher than 25 dB at 4 KHz, but aviation personnel were not
included in the high risk group (Barney & Bohnker 2006).
The noise exposure times of military pilots are usually relatively short when
compared to airline pilots, for example. During normal working conditions, Finnish
military pilots’ usual daily flight time is around 60-90 minutes and total flight hours
during a flight career is approximately 3000 hours, keeping the overall exposure
under the EU limits (Kuronen et al. 2003, Kuronen 2004). The career-long flight
hours of military pilots are similar in several other European countries (EAG2015
course, personal communications). In comparison, many airline pilots log up to 15
000-20 000 flight hours during their career (Finnair/Dr Kimmo Ketola, personal
communications).
Anyhow, the importance of hearing protection in military aviation is clear:
Even though the exposure times are usually short enough to keep the overall
exposure under the EU guidelines, peak levels during flights may exceed the limits.
Also, in the future the noise exposure times of military pilots may increase, due to
increased mission durations. Individual noise sensitivity differs, and noise-sensitive
pilots may be susceptible to hearing impairment due to aviation noise even with the
current overall exposure times (Kuronen 2004).
There is evidence that fighter and helicopter pilots are at increased risk of
hearing impairments when compared to other pilots. A study by Raynal et al. (2006)
compared the hearing levels of fighter pilots, helicopter pilots and military transport
pilots. They noted that at a given age, fighter pilots and helicopter pilots had worse
hearing than transport pilots, even though transport pilots had more flight hours.
Fighter pilots’ audiograms were characterised by a 6 kHz notch, which was worse
in the left ear. Helicopter pilots often had worse hearing threshold also at 3 kHz
when compared to other pilots (Raynal et al. 2006). This increased risk is likely to
47
be caused by higher noise levels in fighters and helicopters. According to a Swedish
study, commercial airline pilots flying aircraft with cockpit noise levels of LeqdB(A)
75-81dB have hearing levels equal to the general age-matched population
(Lindgren et al. 2008). In a study of SNHL rates and trends in US military aviators
between 1997 and 2011, SNHL incident rates were higher among fixed-wing pilots
than helicopter pilots (Orsello et al. 2013). However, contradictory results also
occur: in a Spanish study about military pilot hearing, hearing impairment (a greater
than normal age-related decrease) was a common finding since only less than 20%
of pilots had no evidence of hearing impairment, but more impairments were found
in transport and helicopter pilots than fighter pilots (Lorente et al. 2005).
2.2.6 Other harmful effects of noise: hearing and listening in noise,
signal-to-noise ratio, noise and workload
In addition to NIHL risk, noise also has effects on speech communication and
psychological effects on workload and concentration (Szalma & Hancock 2011).
Noise can be defined as undesired auditory disturbance, as a sound which has no
relationship to the completion of the immediate task (Hawkins 1993), or simply as
a sound that is unpleasant, distracting, unwarranted or in some other way
undesirable (Rood & James 2006b). For hearing speech, noise has several negative
effects: noise can mask the speech signal, limit speech intelligibility, listening can
become laborious, and an increased need for repetition, clarification and reliance
on visual cues are all associated with speech in noise (Gelfand 2009b).
Signal to noise ratio
Signal-to-Noise Ratio (SNR) is expressed in dB of speech above the noise (e.g.
10dB SNR) (Rood 1997). SNR is usually more important for speech intelligibility
than the absolute level of signal or noise (Hawkins 1993). In general, people with
normal hearing can understand speech even at an SNR of -6 to -10dB (Agnew
1999). An increase in speech intelligibility follows a gentle S-shaped curve, as
presented in Figure 11, meaning that when SNR increases, speech intelligibility
also increases until a certain point is reached (Rood 1997). Hearing impairments
complicate the situation considerably; people with hearing impairment require
higher SNR for understanding speech (Beattie et al. 1997, Agnew 1999).
An important issue with SNR is also the context of the speech. SNR sufficient
for speech intelligibility depends on the signal type; for example for digits, even
48
relatively poor SNRs are tolerated without a significant reduction in correctly
understood words, because digits are drawn from a small vocabulary. In
comparison, isolated words without clear contextual information require higher
SNR (Rood 1997).
Fig. 11. Effect of signal-to-noise ratio and the type of the signal to its intelligibility.
(Rood & James 2006a, reprinted with permission)
Other effects of noise - Noise, workload and human performance
Noise has many other harmful effects, which can have a negative effect on
performance especially in challenging situations with several simultaneous tasks.
Noise is associated with an accident risk; exposure to noise levels over 90dB (Leq8h)
is related to an increased accident risk, and hearing impairment further increases
the risk (Toppila et al. 2009, Picard et al. 2008). Noise also impairs information
processing and increases the level of general alertness. Listening to speech in noise
requires mental capacity, is time-consuming and uses cognitive reserves (Rood &
James 2006b, Gelfand 2009b). Poor SNR results in reduced speech intelligibility,
which causes the listener to fill in the gaps in speech based on previous experience,
learning and expectations. If this filling goes wrong, it is called a false hypothesis
error, which is a known flight safety factor (Hawkins 1993).
Noise reduces short-term and working memory performance by distracting
attention away from the task at hand towards the noise stimuli. High-intensity
49
intermittent noise (impulse noise) in particular is considered to be more distracting
than continuous noise. Speech noise appears to be more damaging to performance
than non-speech noise, especially in tasks requiring perceptual and cognitive
capacity (Szalma & Hancock 2011, Rood & James 2006b). Noise exposure is also
associated with an increase in reaction time: In aeroplane mechanics, prolonged
noise exposure (a work week spent on noisy runway conditions) was associated
with an increase in reaction times during the week (Kjellberg et al. 1998).
The deteriorating effect of noise on understanding speech also depends on
whether the listener needs to hear his/her native language or a foreign language.
When the listener is listening to a non-native language, the effect of noise is more
remarkable. In a study by Moore (1996), pilots who listened to their native language
perceived sentences correctly at a lower SNR than non-native pilots (Moore 1996).
In aviation, this issue is important because a large number of people are required to
communicate with their non-native language.
2.2.7 Hearing protection solutions in military aviation
The challenging acoustic environment in military aviation requires several
capabilities from hearing protection solutions. Coping with noise in aviation begins
with the design and manufacturing of the aircraft, which define the aerodynamic
features and amount of insulation in the aircraft. Despite this, the noise levels are
still high, and hearing protection is needed.
In selection of HPDs, several issues need to be considered. HPDs need to
provide sufficient sound attenuation, enable radio communication and hearing of
warning sounds, and to be able to function in rapidly-changing atmospheric
pressure. Some sounds in the cockpit, such as synthetic cockpit voice alarms, are
communicated via loudspeakers in the cockpit, and they should not be attenuated
excessively. During the flight missions the cockpit temperature can vary and
physical workload can cause sweating which needs to be taken into consideration
(Rood 1997). Pre-existing hearing impairments need to be taken into account:
hearing impairments may cause a significant loss in speech intelligibility in cases
when passive HPDs (such as earmuffs) are used (Abel et al. 1982).
Possible hearing protection solutions in military aviation include standard ear
plugs, helmets, headsets, communication earplugs and active noise reduction (ANR)
systems. A combination of these can also be used (Rood & James 2006b,
Pääkkönen & Kuronen 1996).
50
Ear plugs
Standard ear plugs can, in optimal conditions, provide good sound attenuation
capacity (ranging from 10-30 dB, predominantly at the high frequencies). However,
in military aviation environments they have several drawbacks: because they
reduce both low- and high frequency sounds, they also attenuate frequencies that
are important for communication. Their sound attenuation depends largely on how
carefully they are inserted: there can be even 10dB of difference in attenuation
capacity between trained and untrained plug users, and poor fitting is common
(Toivonen et al. 2002). Hearing protection device use training is a rarity: in a study
by Abel (2005) in Canadian Forces, 89% of the respondents reported having had
less than 1 hour of HPD use training during their entire military career. Half of the
respondents judged training as ‘non-existent’ or of poor quality. If standard ear
plugs are correctly inserted and thus air-tight, rapid altitude changes (resulting in
changes in surrounding pressure) become a problem because they may create
trapped air between the plug and tympanic membrane and cause barotrauma (Bragg
& Danford 1972).
Flight helmets
Flight helmets with circumaural hearing protectors are commonly used in military
aviation especially in fighters, fighter trainers and helicopters, and in some
transport /liaison aircrafts (Rood 1997). They are the natural choice in these
aircrafts because they have other functions in addition to hearing protection: they
provide head protection, a mounting for an oxygen mask, visor, head-mounted
displays and night vision goggles. Even though hearing protection and
communication systems are the only features required continuously when the
helmet is used (compared to head protection capabilities, for example, which
hopefully are never needed), these other requirements may limit the hearing
protection possibilities. For example, helmet weight added to all other devices
cannot be increased too much without causing a risk to pilots’ cervical spines
(Sovelius 2014).
Flight helmets used in the Finnish Air Forces (FinAF) provide noise
attenuation of approximately 10-25dB, predominantly at the high frequencies (Fig.
12). Low-frequency noise, which dominates in aircraft, is problematic because
attenuation abilities are considerably lower in low-frequency noise (0-6 dB
depending on the helmet and aircraft) (Pääkkönen & Kuronen 1996). Therefore,
51
pilots are quite well protected from mid- to high-frequency noise, but protection
from low-frequency noise is poorer.
New helmet types such as the Joint Helmet Mounted Cueing System (JHMCS)
were introduced to military aviation in 2003-2004. These helmets can give
information from the direction the pilot is looking, and they are also used for aiming
at the target. These new features have several benefits, but they also cause an
increased need for head movements compared to previous helmet types, and
therefore the helmet needs to be lighter due to prevent cervical spine risks. This has
resulted in decreased sound attenuation capacity. Pilots have complained about
poor sound attenuation and noise when using these helmets (Gallagher & McKinley
2010).
Headsets
Headsets are another form of circumaural hearing protectors. They are used in
propeller aircraft, transport and cargo aircraft, as well as in civilian passenger
aircrafts. The earmuffs and headsets used in the FDF can provide good (up to 3035dB) attenuation of frequencies higher than 500 Hz, but also with headsets the
attenuation capacity is poor at low frequencies. The headsets lack other functions
provided by flight helmets (head protection, mountings of oxygen masks and headmounted devices) and therefore are not useful in fighter aircraft (Pääkkönen &
Kuronen 1996).
52
Fig. 12. Summary of sound attenuation capacity of some helmets and headsets used in
military aviation. Attenuation data for the Alpha helmet, Gentex ACS helmet and
Ampliguard headset adopted from the article by Pääkkönen & Kuronen (1996), for the
Gentex HGU-P55 helmet from the manufacturers product information and for JHMCS
from (Gallagher & McKinley 2010).
Double hearing protection
Combinations of ear plugs and headsets or helmets have also been used in military
aviation. In a study where earplugs, earmuffs and their combination were studied,
the double hearing protection was shown to be very effective in terms of sound
attenuation (attenuation was up to 37-50dB, depending on the frequency) (Abel &
Odell 2006). However, in the same study it was observed that double hearing
protection has negative effect on communication: a significant decrease from 9092% to 75% in consonant discrimination was observed with double hearing
protection (Abel & Odell 2006). In another study, where speech audiometry using
one-syllable words was performed with headsets and with a headsets plus earplugcombination, a substantial decrease in word intelligibility was noted with double
hearing protection (Wagstaff & Woxen 2001).
53
Active noise reduction (ANR)
ANR systems are currently available in aviation headsets and in some helmets. In
ANR systems, noise inside the hearing protection device is sampled with a
microphone and emitted in inverted phase, to cancel the original noise. ANR
systems are effective in low-frequency noise, and they can provide a good addition
in attenuation of headsets. Therefore, they are an attractive option for hearing
protection, especially in helicopter and piston engine aircraft, where low-frequency
noise dominates (Wagstaff & Woxen 1997). In the study by Pääkkönen and
Kuronen (1996), an ANR system added to a flight helmet improved noise
attenuation by 3-19 dB in the 63-500 Hz frequency range. However, findings of
amplification of noise on mid- and possibly higher frequencies has been noted in a
study by Wagstaff & Woxen (1997). In the same study, augmentation of intercom
audio signals was seen to occur for some subjects. It therefore seems that ANR
systems have positive aspects and their use is increasing, but they have some
characteristics which need to be taken into account depending on the aircraft type
(Rood & James 2006b). FinAF uses ANR in headsets used in C295M transport
aircraft and in Pilatus12NG light transport aircraft.
Communication ear plugs (CEP)
Communication ear plugs (CEP) are increasingly used for hearing protection and
the enhancement of radio communication. The first CEPs consisted of a miniature
transducer and a replaceable foam ear plug (Mozo & Ribera 1997, Rajguru 2013).
Nowadays, several manufacturers offer different CEP types, and the custommoulded type (custom-moulded communication ear plug, m-CEP) is being used in
increasing numbers. The m-CEP system consists of a custom-moulded ear plug,
and a small receiver which is connected to the helmet via cable and which delivers
communication from the aircraft’s communication system directly to the ear canal.
In CEPs, as with standard ear plugs, the plug needs to allow pressure to equalise
between the tympanic membrane and the plug to prevent trapped air and
barotrauma. The m-CEP manufacturers have solved this problem by including
pressure equalising vents to their devices (Finnish Institute of Occupational Health
2013).
Pilots have reported improved speech intelligibility while using m-CEPs
(Steinman 2012, Pascoe 2013). However, reports about discomfort issues and other
problems leading to unwillingness to use them have been published. Koda et al.
54
(2009) reported in his abstract that 16% of F-22 Raptor pilots preferred not to use
CEPs, 81% of the pilots had faced problems with them, and 78% had experienced
discomfort issues. Pilots have also reported problems in adapting to the use of CEP
systems (Steinman 2012) and irritation with the foam tips used in CEPs (Steinman
2013).
2.3
Radio communication in military aviation
2.3.1 Basics of aviation radio communication
If overly simplified, all speech communication between two people can be cut
down into two parts (Fig.13) (Rood & James 2006a):
Fig. 13. The two interfaces in speech communication (Rood & James 2006a)
In aviation radio communication, the start- and endpoints remain the same.
However, due to the nature of the radio communication, flight environment and
several technical solutions required for delivering a message from one pilot to
another, many additional factors may have an effect on communication (Fig. 14).
Fig. 14. Speech communication in military aviation via radio, and examples of factors
that may have an influence on communication.
55
The goal for aviation radio communication is to ensure flight safety by
unambiguous pilot-controller communication and to support operational efficiency
(ICAO 2009). Radio speech communication in aviation is characterized by normalhearing subjects communicating via radio, usually without visual contact. The
international language used is English, but regional languages can also be used (e.g.
Finnish in Finnish airspace).
To ensure that radio communication is safe and efficient, ICAO has established
guidelines for aeronautical telecommunication (ICAO 2001). These guidelines
instruct the use of language in radio communication in aviation. They are also used
in military aviation, with some military-specific additions, such as several tactical
phraseologies (e.g. NATOs Multiservice Tactical Brevity Codes).
The standardised aviation phraseology includes instructions on numbers,
alphabets, call signs, certain critical messages, such as clearances and messages
requiring read back or acknowledging. There are also instructions about speech rate,
which should not exceed 100 words / minute (ICAO 2001, Eurocontrol 2011).
In two-way radio communication, several technical systems are used, and they
make the communication different from everyday speech. Aviation radio systems
allow only one speaker at a time to be active, and additional transmission attempts
and overlapping speech are not possible. Radio transmission is initiated either by
pushing a tangent of the microphone or by automated speech-initiated activity. In
either system, there is always a short interval before the transmission starts, and if
speech is initiated before this interval is over, the start of the message is inaudible.
The frequency range of aviation radio communication systems’ typically
covers approximately 0.3-3.4kHz (Rood & James 2006b), which results in highfrequency consonants (k, p, s, t) being vulnerable in communication. Failures in
technical equipment (both at the senders and receivers side, in e.g. microphones
and loudspeakers), as well as disturbances in radio signals due to a weak signal,
long distance or (in military aviation) jamming the frequency can also deteriorate
communication.
In addition to technical issues, radio speech fundamentally differs from
everyday speech. In radio communication, there is usually no visual contact
between the speakers. This means that the non-verbal information exchange which
is natural during everyday communication (such as facial expressions, noddings
and direction of gaze) is not available. Therefore, in radio communication,
processes in e.g. turn taking in speaking, keeping one’s turn and giving turn to the
next speaker need to be established clearly. Similar differences occur in identifying
the speaker and recipient. The only way to pick a speaker or recipient is to identify
56
him directly by using call signs, and ensuring that a message has been heard
requires an acknowledgement or read back. Standardised radio phraseology is
beneficial in these situations: it assists speakers to address the correct recipient, to
select and time their own speaking turns, and it keeps the communication short and
punctual. Using the correct phraseology is also beneficial in noisy situations and
with poor SNR: because the number of sayings in standard phraseology is limited,
hearing the message completely is often not necessary in order to understand the
meaning (Rood & James 2006a, Fairburn et al. 1999).
Communication errors and flight safety
Radio communication is an important factor in flight safety. Radio communication
errors have been a causal factor in several aviation accidents. For example, the
deadliest accident in aviation history, the collision of two Boeing 747 aircraft on a
runway that killed 583 people in 1977, was largely caused by radio communication
errors (Cushing 1994). Even though the communication standards and methods
have improved since this accident, communication errors still remain the most
prevalent causal factor for flight level violations and runway incursions (ICAO
2011). In military aviation, a study about United States Air Force’s recent aviation
accidents, coordination and communication factors were a common finding,
especially in controlled flight into terrain accidents and mid-air collisions (Gibb &
Olson 2008). Simply maintaining some kind of radio communication is not enough:
in civil aviation mid-air collisions radio communication was maintained in 40% of
the collisions studied, but still the accidents could not be prevented (De Voogt &
Van Doorn 2006).
Radio communication is also important for achieving good SA (Salas et al.
1995). Communication is needed for distributing relevant situation information to
others, and for confirming and cross-checking information (Endsley & Jones 1997,
Kanki et al. 1989, Salas et al. 1995). Improving team communication processes is
widely accepted as a way to improve mission and team performance (Hutchins et
al. 1999). Both the communication quantity and quality have a role, but the effect
of these on team performance are dependent on situation. A high level of
communication (quantity) has been shown to correlate positively with better team
performance (Sperling & Pritchett 2011). On the other hand, a continuous flow of
communication may take up working memory capacity and distract problem
solving (Patrick et al. 2006).
57
A topic that has received little attention is the lack of communication. Even
though it is difficult to study, there is evidence that it can be dangerous. In a survey
studying the primary causes of fatal aviation accidents by Campbell & Bagshaw
(2002) the primary cause was inadequate communication in 41% of cases.
Characteristics of good radio communication
Successful radio communication requires both effectively-functioning radio
equipment and human proficiency, understanding of the significance of following
phraseology and other factors related to communication on a radio band.
The quantity of communication is an important issue: the purpose of
communication is, ultimately, to deliver the required information from the sender
to the receiver. A high amount of communication has been associated with a
positive team outcome. In a study in which helicopter pilots were forced to increase
communication by blocking the visibility of the instrument panel of the other pilot,
an increase in communication had a positive effect on the mission performance and
workload (Sperling & Pritchett 2011). In a fast jet simulator, speech act frequency
correlated with a positive outcome of the mission (Svensson & Andersson 2006).
Communication training appears to be beneficial. The earliest reports that
teams who had been trained for communication perform better than teams without
training were published already in the 1970s (Rafferty et al. 2010), and Sexton &
Helmreich (2000) suggest that effective communicating styles might be trainable.
The quality of aviation communication depends on all parts of the
communication: the sender, the message itself and the receiver of the message
(Campbell & Bagshaw 2002). The following characteristics have been recognised
as being important:
The sender
–
–
–
–
–
58
should use explicit content. The message should be planned ahead and the
sender should articulate clearly (Orasanu 1994, Hutchins et al. 1999);
should use standard phraseology, standard communication patterns and
predictable messages (Hutchins et al. 1999, Kanki et al. 1989);
should not use excess verbiage (Hutchins et al. 1999);
should clearly identify the speaker and the receiver (Hutchins et al. 1999);
should be goal-oriented. The focus is to promote a shared understanding of the
problem and problem-solving strategies (Orasanu 1994).
The message
–
–
should contain homogenous, conventional speech patterns and standard
phraseology (Hutchins et al. 1999);
should not contain too much information in one message (Morrow et al. 1993,
Cardosi et al. 1998).
The receiver
–
–
–
–
needs to have sufficient SNR (Rood & James 2006a);
needs to have a workload situation and working memory capacity sufficient for
understanding (Fairburn et al. 1999);
should pay attention to messages requiring read back/hear back. (Cardosi et al.
1998);
should acknowledge received message (Orasanu 1994, Hutchins et al. 1999).
An acknowledgement signals that the recipient has heard and understood the
message. When acknowledgements are used correctly, absence of an
acknowledgement indicates a failure in communication.
2.3.2 Radio communication problems: some typical error types and
their consequences
Problems in radio communication can be caused by the behaviour of the speakers,
technical issues or a combination of these. Standard phraseology is often not used
as instructed. One obvious reason for this is that the phraseology cannot include
standardised sayings for all possible situations. Thus, there will always be situations
in which plain English needs to be used. However, radio communication is often
modified, even in those situations in which a standardised phrase would exist.
Most of the research about radio communication errors and deviations is done
by studying incidents and close-call situations, and focus on pilot-ATCcommunication (Grayson & Billings 1981, Prinzo & Britton 1993, Van Es 2004,
IATA2015). As early as in the 1980s, Grayson and Billings (1981) found out from
reports of NASA Aviation Safety Reporting System that pilot-controller
communication problems are very common. In their study investigating 5400
aviation safety reports, they found that the radio communication problems between
pilots and ATC clustered around ten categories:
1.
2.
Misinterpretable – phonetic similarity
Inaccurate – transposition
59
3.
4.
5.
6.
7.
8.
9.
10.
Other inaccuracies in content
Incomplete content
Ambiguous phraseology
Untimely transmission
Garbled (or blurred) phraseology
Absent – not sent
Absent – equipment failure
Recipient not monitoring
Of these, the three most common problems were 1) other inaccuracies in content,
2) untimely transmissions, and 3) recipient not monitoring. In addition, missing
messages (category ‘absent-not sent’) was very common, but a high number of
these was explained by the somewhat broad interpretation of ‘an absent message’
(Grayson and Billings 1981).
Later, in a study by Durso et al. (1988) about ATC separation errors (situations
where the ATC was unable to keep a distance between aircraft in required limits),
communication errors were the second-most common reason for separation errors
(only problems with radar display data occurred more frequently). Read back errors
were present in 21%, acknowledgement errors in 7.1%, misunderstandings in 5%
and phraseology errors in 4% of the separation violations. Especially in situations
where the controller was unaware of the separation violation, communication
problems were frequent (Durso et al. 1998).
There is less information about communication problems during routine
situations – obviously it is more difficult to study communication in situations that
went normally without any incident requiring official reporting. However, even
during normal operations radio communication problems are common. In a survey
conducted by International Air Transport Association (IATA) with 2070 civilian
airline pilots, 44% of the pilots reported a standard phraseology error occurring at
least once on every flight. These deviations were usually reported only if the pilot
felt that it affected flight safety, and thus the majority of them are not reported
(IATA 2011). Morrow et al. (1993) studied problems in routine pilot – ATCcommunications in a field study, and noticed that procedural errors (e.g. missing
call signs, read backs or acknowledgements) occurred during 3-13% of the
communications, and inaccuracies during 1% of the routine communications. In
Finland, Eskelinen-Rönkä (2005) noticed that during routine pilot-ATC
communications almost 2% of the communications consist of unofficial greetings
(e.g. good morning, bye, see you) which are not a part of official phraseology.
60
Approximately 0.5% of the communications were unclear or inaudible, and in some
standardised sayings (e.g. numbers), the incorrect or shortened version was used
very often, with some accounting for up to 25% of the sayings.
In military aviation, speech during fighter missions with Finnish fighter pilots
has been studied by Keränen (2005). In his study, with four fighter pilots and a
fighter controller participating in an air combat training mission (real flight),
missing or inconsistent use of acknowledgements was observed to be common:
during some (usually the most intense) flight phases, up to 8-10 acknowledgements
per minute were missing (Keränen 2005).
The following non-ideal radio communication patterns have been shown to be
associated with certain communication errors:
–
–
–
–
–
–
Excessive message length: long messages and messages containing many types
of information in one message (e.g. command and information) often result in
incorrect or partial read back (Morrow et al. 1993). Overlapping speech is
common after excessively long messages, because after a long transmission
many speakers attempt to initiate a new transmission. This can cause a
complete loss for short messages such as numbers and call signs (Svensson &
Andersson 2006)
Message formulation: if a message requires different types of responses (e.g.
acknowledgement and read back), it is often associated with incorrect or partial
read back (Morrow et al. 1993). An increase in the amount of information in
one message is associated with an increase in prioritising and comprehension
errors (Morris & Leung 2006).
Non-routine messages: incorrect phraseology correlates with incorrect read
back (Morrow et al. 1993)
Missing acknowledgements: failure to acknowledge messages results in
reduced communication efficiency, because the senders tend to repeat
unacknowledged messages (Morrow et al. 1993). If acknowledgements are not
used or their use is inconsistent, a missing acknowledgement loses its ability
to signal that something is going wrong in the communication (Keränen 2005).
Read back-hear back- errors: an incorrectly read back message is not always
noticed and corrected. One reason for this is the tendency for the sender to
expect the correct read back (Cardosi et al. 1998)
Not using call signs, and call signs that sound similar: Turn-taking in radio
communication becomes unclear (Cardosi et al. 1998).
61
2.3.3 Workload and radio communication
An increase in workload has been shown to cause many changes in radio speech.
A rise in pitch (fundamental frequency (F0) of speech), an increase in volume and
a faster articulation rate have been identified by many researchers (Brenner et al.
1994, Griffin & Williams 1987, Huttunen et al. 2011b, Johannes et al. 2000,
Mendoza & Carballo 1998). These changes can also be intentionally used by fighter
pilots to prioritise information in intense air combat situations. There are, as
expected, great differences between individuals in the effect of workload on radio
speech.
High workload has been shown to have a deteriorating effect on
communication and team SA. In an experimental study simulating the control room
of a nuclear reactor, communications breakdown usually occurred in situations of
high workload (Patrick et al. 2006). In another study, the communicative behaviour
of civil pilots at differing workload levels in real flights was studied. The in-flight
situations were categorised into five risk levels: low and high workload in normal
situation and three danger situation levels (ranging from minor incidents to critical
scenarios such as losing vital systems of the aeroplane). Increased workload
resulted in changes especially in communication categories considering initiation
of crew resources, receptiveness and information quality. With high workload,
communicative remarks decreased and short remarks increased, and a decreased
ability to react to information from different sources was observed. In addition,
coherence of messages suffered, questions were left unanswered, crew members
talked about different matters and interrupted each other. (Silberstein & Dietrich
2003)
62
3
Aims of this study
The purpose of this study is to gain an understanding of the prevalence of and
significance of radio communication problems in Finnish military aviation, and to
analyse whether one newly adopted hearing protection system is functional and
could ease the issues. This study is performed in a fighter simulator by analysing
the effect of workload on radio communication, and with survey studies addressing
the prevalence and types of radio communication problems and the characteristics
of one new hearing protection solution. The findings are then discussed from a
human factors perspective with HFACS. The following issues were studied:
1.
2.
3.
4.
Fighter pilot workload and workload changes during a simulated air combat
were studied in a flight simulator by assessing the correlation between the
difficulty of a flight phase and heart rate changes (Study I).
The effects of different workload levels on radio communication, to determine
what kind of changes a mentally demanding flight phase has on radio
communication were studied in the same simulated air combat (Study II).
The type and occurrence of aviation radio communication problems, incidents
related to radio communication problems and attitudes towards hearing
protection in Finnish Defence Forces aviation were studied using a survey
study (Study III).
The advantages, benefits and problems associated with a new hearing
protection solution (moulded communication ear plugs) used by military pilots
were studied using a survey study (Study IV).
63
64
4
Subjects and methods
4.1
Subjects
4.1.1 Subjects in simulator studies
For the simulator studies (I and II), 15 male military pilots were recruited. Only
males were recruited because at the time of the study the majority of Finnish
military pilots were male. The participants were 25-34 years old (mean 28) and all
had active flying status. The pilots were stationed at three different fighter
squadrons in Finland, with five subjects at each. The total flight experience was
570–1400 hours (median 900), of which the mean number of F-18 Hornet flight
hours was 170–650 (median 300). All the pilots had passed an annual physical
examination and were in good health.
In Study II, the radio speech communication of these same 15 pilots was
analysed. Due to unexpected failure in recording the audio and video signals, data
needed for speech rate calculation of one subject and video data for cognitive load
evaluation for another subject was not obtained. Therefore in Study II, the number
of participants was 15 for analysis of the content of radio communication, and 14
for the speech rate and cognitive load analysis.
4.1.2 Subjects in survey studies
For Study III (Radio speech communication problems in military aviation- survey)
a total of 225 questionnaires were sent to flying squadrons of the FDF. A total of
169 pilots returned the questionnaire, of them 138 were fixed-wing pilots and 31
helicopter pilots. The response rate was 75%, ranging from 61% to 100% in
different squadrons.
For Study IV (Moulded communication earplugs in military aviation- survey)
a total of 247 questionnaires were sent to flying squadrons of the FDF. A total of
146 pilots responded to the survey, 127 fixed-wing pilots and 19 helicopter pilots.
The response rate was 59%.
65
4.2
Flight simulator studies (I & II)
4.2.1 Flight simulator
The flight simulator used for the Studies I and II was a Weapons Tactics Trainer
(WTT) simulator of an F/A-18C Hornet (L-3 Communications Link Simulation &
Training, New York, USA). The simulator is a static dome simulator. Inside a dome
(diameter 12m) is a cockpit of an F/A-18C Hornet, and a virtual flight scene is
generated by video projectors on the inside of the dome. The flight instructor,
wingman and fighter controller had their own working positions outside the
simulator.
4.2.2 Simulated flight mission (Studies I & II), reading tasks (Studies
I & II), cognitive load analysis (Study II)
The flight simulator study began with a 5-minute seated rest period for all the pilots
as a control. During this period the pilots were sitting in the simulator wearing their
flight gear and measurement devices. After the seated rest, pilots performed a short
2-minute reading task reading numbers and commands in Finnish and English (for
the formant analyses which have been analysed by other researchers). The short
reading task was followed by either a simulated air combat mission or a control
reading task (20min), during which the pilots sat in the simulator listening to and
reading aviation phraseology to the radio. This control reading task was
counterbalanced (8 pilots had the flight mission first and 7 pilots took the control
reading task first) to control the effect of test situations on HR and speech
measurements.
For the simulated air combat mission, the pilots’ task was to fly as the leader
of two F/A-18C Hornets. The mission was a simulated war-time flight mission,
which started airborne (Combat Air Patrol, CAP). The flight mission consisted of
air-to-air combat with fighter enemy aircraft pairs followed by a formation of
multiple enemy aircraft, and then a break-off from combat, return towards base,
instrument landing system (ILS) approach in minimum weather conditions and
landing. The detailed phases of the flight mission are presented in Table 1. The
flight mission was designed to be very demanding even for experienced pilots: it
included several air-to-air combats with an enemy, some close range air combat,
and ILS landing in poor weather, which are all challenging tasks. In addition to
these, the pilots were also responsible for leading the fighter team, planning the
66
strategy and giving orders and instructions to the wingman. When compared to
tasks in civil aviation, an ILS approach and landing in poor weather is similar to
the latter part of this simulated mission (phases 11-15). The start and scenario of
the flight mission was similar for all subjects, but the flights became unique for all
subjects, because the tactical decisions the pilots made resulted in a different
realisation of events. This resulted in some differences between the individual
workload during the flights, as well as in different number of flight phases for some
pilots.
The flight phases were distributed differently for Studies I and II (Table 1). For
heart rate (HR) and delta heart rate (ΔHR) analysis (Study I), the original 16 phases
were used. For the qualitative communication analysis (Study II) the phases were
combined into four longer phases, which represent the different events of the flight,
to enable communication analysis.
Table 1. Flight phases in Study I and Study II
Phase nr
Study I flight phase
Study II flight phase
Description
1
5 min seated rest
2
Reading task 1 (2min)
3
Start of flight, CAP
Start
Start of flight airborne in CAP,
information of enemy, tactics planning
4
Tactical manoeuvre
Combat 1
Heading towards first interception
5
Beyond visual range
interception
Combat 1
Beyond visual range combat with
enemy fighters
6
Tactical manoeuvre
Combat 1
Tactical manoeuvre
7
Beyond visual range
interception
Combat 2
Heading and intercepting next enemy
fighters
8
Tactical manoeuvre
Combat 2
Tactical manoeuvre
9
Interception of
formation
Combat 2
Interception of escorted enemy aircraft
formation (several enemies)
10
Break-off from combat
Return to base & landing
Break-off from combat, heading
towards home base
11
Return to base (high)
Return to base & landing
Return to base at high altitude
12
Return to base (low)
Return to base & landing
Return to base at low altitude
13
Initial ILS
Return to base & landing
ILS initial approach
14
Intermediate ILS
Return to base & landing
Intermediate ILS approach (vectors)
15
Final ILS and landing
Return to base & landing
16
Reading task 2 (20min)
Final ILS approach and landing
Reading task 20 min *Counterbalanced
67
Cognitive load analysis (Study II)
For Study II, the cognitive load was quantified by an experienced F/A-18 Hornet
flight instructor. The instructor assessed the overall workload by evaluating three
parameters of overall cognitive load individually for each pilot and each flight
phase on the visual analogue scale (VAS) (a 100 mm horizontal line, on which the
left end of the line means no load at all and the right end of the line represents the
highest imaginable load). Video data for cognitive load evaluation was available
for 14 subjects. The detailed information about the cognitive load analysis process
is described in Huttunen et al. 2011a and Huttunen et al. 2011b. The three
parameters of overall cognitive load were:
1.
2.
3.
Situation awareness load (SA load), which consists of three main components
of SA (perception of elements, comprehension of their meaning and projection
of the information to the future status);
Information load (INF load), which includes the amount, complexity and
criticality of information;
Decision-making load (DEC load), which describes the amount and criticality
of decisions to be made, and how many choices were available from which the
decision had to be selected.
The mean values for workload parameters in different flight phases are shown in
Figure 15. The phases Combat 1 and Combat 2 had significantly higher workload
scores when compared to the Start and Return to base phases.
68
Fig. 15. Cognitive load scores for Study II. Mean scores of different components of
cognitive load on the visual analogue scale VAS of 0-100 (with 95% confidence intervals)
as evaluated by the flight instructor. N=14. SA load= situation awareness load, INF load=
information load, DEC load= decision-making load.
4.2.3 Heart rate measurements (Study I)
Heart rate (HR) analysis was used because it does not require invasive methods and
it has been shown to be functional in aviation circumstances. HR was continuously
measured with a small portable digital ECG recorder (Oxford Medilog FD-4,
Oxford Instruments Medical System, Abingdon, UK). ECG leads of modified V1,
V5, and aVF were used. The ECG data was analysed with a Win-CPRS application
(Absolute Aliens Inc., Turku, Finland). The artefacts in ECG were removed with
the software, and then R-R intervals were stored and used for calculating HR (For
more detailed description, see Hannula et al. 2008). For HR analysis, deltaHR
(ΔHR) was calculated for every subject. ΔHR is the difference between HR during
simulated flight and the lowest HR obtained during seated rest (the closest estimate
of the resting HR that could be obtained in the study situation). ΔHR was then used
in the analysis.
69
4.2.4 Flight performance measurements (Study I)
An experienced flight instructor rated all the flights with the flight performance
scale used in the FinAF as a daily evaluation tool. The scale is a numerical one,
from 1 to 5, with intervals of 0.25 intervals. The flight instructor gave an overall
flight performance score, and a separate score for different interception phases, fire
accuracy parameters, battle geometrics, break off from combat, ILS approach and
landing, and for leading the pair and overall radio communication. The flight
instructor was the same for all the subjects. The instructor had previously worked
with all the subjects, but he did not have daily working experience with them.
4.2.5 Communication analysis (Study II)
In Study II, the subjects performed a simulated air combat flight mission described
in section 4.2.3. The pilots’ task was to fly the mission as a leader of an F/A-18C
Hornet two-ship formation. Two other speakers participated in the mission: a
wingman in another F/A-18C simulator and a fighter controller. At the end of the
simulated flight mission, the pilots also communicated with ATC, but the fighter
controller was no longer communicating, and thus the maximum number of
speakers was three at a time. A data link was not used during the simulated flight.
All participants communicated on the same radio frequency band. The language
used during the flight mission was mainly Finnish (although some pilots
independently switched to English during the ILS approach when they talked with
ATC).
The speech communication during the simulated flight mission was recorded
with a mask microphone and video camera. Data for speech rate calculation was
available for 14 subjects. From the video and audio recordings, all speech
communication was transcribed into Excel files. In order to obtain information on
the amount of speech, the number of messages and syllables was calculated. In this
study, syllables are used instead of words to calculate speech rate because the
Finnish language is characterised by longer words than many other languages
(Lehtonen 1970), which enables better comparability with other languages.
For analysing communication, the messages were divided into four categories
(informing, commands, requesting, acknowledgement), depending on their type.
These categories were chosen to enable comparison with in-flight communication
analysis results studied previously in the FinAF (Keränen 2005). The categorisation
of the messages was performed by the author. For ensuring the reliability of
70
message categorisation, coding reliability was evaluated by having one experienced
pilot and one linguist categorise the communication of two randomly selected
flights (altogether 425 messages). The agreement rate was then calculated between
the author and both other coders. The agreement rate was 87% between the author
and the experienced pilot, and 91% between the author and the linguist, indicating
a good agreement.
The message categories were:
Informing: Message to deliver information. E.g. the pilot is informing his own
location, action or plans, or the fighter controller informs the pilot about enemy
action or location. ‘Enemy aircraft 110 degrees 5 miles’.
Commands: Orders. Message types that obligate the recipient to act. The
section leader, fighter controller, or air traffic controller orders to the pilot. For
example, the section leader commands his wingman ‘kilo 03 two-ship heading 340’.
Requesting: Questions, requests. Information requests, repeat requests. ‘Zero
four your location?’, ‘Where is the enemy?’, ‘Repeat’.
Acknowledgement: Acknowledging the other message types, e.g. by using own
call sign. Read back messages.
Other: Other messages that cannot be categorised in the above categories. For
example, mumbling to the microphone, the pilots speaking to themselves,
unaddressed talk.
Unclear: Unclear message.
Many: The message includes several different message types.
4.3
Survey studies
4.3.1 Radio speech communication in military aviation - survey
(Study III)
A questionnaire consisting of 34 questions (including 11 background questions and
23 questions about radio speech communication), was constructed and sent to all
flying squadrons of the FDF in 2007. The subjects answered anonymously. The
questions were selected based on the previous knowledge and literature about radio
speech communication problems and hearing issues related to military aviation
working environments. Before use, the questionnaire was commented on by flight
instructors and some staff officers of the FinAF, and piloted with some flight
instructors from a different organization (Patria Pilot Training, Tikkakoski,
71
Finland). Based on the feedback, the content of the survey was revised and focused
on the work assignments of the pilots
The detailed questions are presented in Appendix 1. The questions covered
background information, questions about radio speech communication problems,
speech rates, speech characteristics and near-miss / dangerous situations related to
radio speech communication, and some other issues. The survey included different
types of questions; in background questions there were questions on category and
interval scales, and about the background of the respondents. In the study questions,
mainly categorical and ordinal scale questions were used. The amount of
communication problems was enquired by using an interval scale. The subjects
were also asked to comment on experiences with speech communication and future
wishes concerning speech communication and hearing protection. In the question
considering near-miss situations, dangerous situations and accidents, the subjects
were asked to report all incidents, even those they considered minor and which they
had not reported officially. Space for free comments was available after the
questions.
4.3.2 Moulded communication earplugs in military aviation - survey
(Study IV)
Moulded Communication Earplugs (m-CEPs) were introduced to daily use for the
FDF pilots in 2008, approximately one year after the speech communication survey
(Study III) described above. Therefore, a survey on the use of m-CEPs was
conducted in the F/A-18C Hornet fighter, Hawk fighter trainer, helicopter, Vinka
trainer and transport aircraft units of the FDF in 2012, five years after the speech
communication survey (Study III). The questions are presented in Appendix 2. The
questionnaire was conducted anonymously. The questionnaire was constructed for
analysing m-CEP-related issues, but it also included some questions asked in Study
III (questions about radio communication problem prevalence, most problematic
flight types, and background noise) so that problem trends could be assessed.
The m-CEP type available for pilots during the time of the survey was
OMARA (Amplifon, Switzerland) (Fig.16). Its ear plug is custom-moulded and
made of silicon. This m-CEP type is used with a flight helmet, and it reduces
background noise levels by 5 dB on average, especially at mid and high frequencies
(Finnish Institute of Occupational Health 2007).
72
Fig. 16. M-CEP type (Omara ®) used in Finland at the time of the Study IV (Reprinted
with the permission of Amplifon, Switzerland)
The m-CEP survey included 31 questions: 12 background questions, five questions
about radio communication problems in general, and 14 questions related to mCEP. The questions are presented in Appendix 2. The administration of the
questionnaires at unit level was organised by aviation safety officers. Helmet types
available for pilots at the time of the m-CEP survey included the JHMCS, Gentex
ACS and Alpha helmet.
4.4
Statistical analysis (Studies I-IV)
SPSS for Windows and Excel for Windows applications were used for statistical
analysis. Excel was used for simple calculations such as descriptives, and SPSS for
statistical analyses (version 12.0 for Study I, version 16.0 for Studies III-IV and
version 22.0 for Study II). In Studies II-IV, P-values of less than 0.05 were
considered statistically significant. In Study I, only P-values less of than 0.01 were
considered statistically significant because several pairwise comparisons were
conducted. A trained biostatistician was consulted for the analyses.
Study I: ΔHR was calculated for every subject by subtracting the HR obtained
during seated rest (phase 1) from the HR obtained in flight. For statistical analysis,
a t-test analysis of repeated measurements was used for statistical testing of the
differences in ΔHR between the flight and control phases. A two-independentgroup t-test was used to compare the ΔHR of the experienced and less experienced
pilots. Kendall’s tau correlation coefficients were calculated to examine the
relationship between ΔHR and flight performance in different flight phases.
73
Study II: Because the duration of the four flight phases varied between the
pilots depending on the tactical choices they made, the relative proportion of each
message type was calculated for analysing the communication profiles in each of
the flight phases. To examine the differences in message and syllable frequency
(for the calculation of speech rate), messages/minute (all speakers),
syllables/second (pilots only) and Finnish words/minute (pilots only) were
calculated. Repeated measures ANOVA with Bonferroni correction as the post hoc
test was used to compare the messages/minute and syllables/second. Repeated
measures ANOVA with Bonferroni correction was also used for analysing the
relative proportion of each message type in different flight phases. In analysing the
relative proportion of the message types in different flight phases, results from the
less conservative LSD correction are also reported for those flight phases in which
a statistically significant difference in overall P-value was observed, but pairwise
comparisons turn non-significant when conservative Bonferroni correction was
used.
Study III: The respondents were divided into fighter pilots, other fixed-wing
pilots and helicopter pilots, depending on the current aircraft type they reported.
Yes/no questions were analysed by using descriptives. For comparing different
pilot groups, Chi-square test, Fisher’s exact test, Kruskal Wallis test, and Conover’s
test as a post hoc test for Kruskal Wallis were used. In the question concerning the
flight type with the most communication problems, the different pilot groups were
analysed using Fisher’s exact test (paired comparison) and the P-values were
corrected with the Bonferroni correction. Descriptions about near-miss and
dangerous situations and accidents, along with the answers to the open questions,
were analysed qualitatively. For analysing the near-misses and dangerous situations,
these were combined into one variable (‘an incident’). Logistic regression analysis
was then used to examine the association between relevant background factors and
the prevalence of communication problems with these incidents.
Study IV: When needed, the pilots were divided into fixed-wing pilots and
helicopter pilots according to their current aircraft type. For certain questions, agegroup division was also used. The age groups used were 20-29 years, 30-39 years
and 40-49 years, and the sole subject aged over 50 years was excluded from age
group comparisons. For analysing the amount of current hearing problems, a
variable labelled “any current hearing problems” was calculated. A pilot was
categorized in this group if he had reported current problems with hearing, hearing
impairment, or any ear disease. During this survey, only one m-CEP type (OMARA
®, Amplifon, Switzerland) was in use in Finland. When analysing questions
74
addressing issues related to m-CEPs, only answers from pilots who had used or
tried m-CEPs were included. In the question considering the amount of discomfort
issues, a new variable (any discomfort issues) was calculated for analysing the total
amount of discomfort issues. A pilot belonged to this group if he had reported to
have any of the following: discomfort in the outer ear, discomfort in the ear canal,
helmet causing pressure, or plug feels loose. Descriptive statistics were used to
determine how often the subjects used m-CEPs, how common radio
communication problems were, and for the yes/no questions. A Chi-square test was
used to calculate differences for yes/no and ordinal scale questions. Descriptions
about incidents or dangerous situations were analysed qualitatively.
4.5
Ethical issues
The study belongs to a larger research project (PURE – speech recognition in
demanding tasks) which has been approved by the ethical review board of the
Northern Ostrobothnia Hospital District, Finland. Survey studies were registered in
advance by the FDF Medical Research Register and approved by the FinAF
headquarters. The subjects in the experimental simulator studies participated
voluntarily and signed informed consent forms prior to their participation. The
survey studies were anonymous. All data (the recordings from the simulated flights
and original survey forms) will be kept confidential permanently and after this
project they will be stored in the FDF archives. Individual subjects cannot be
identified from the results.
75
76
5
Results and Comments
5.1
Studies I & II: Pilot workload, associated heart rate changes
and radio communication changes in flight simulator
5.1.1 Heart rate (HR) and workload issues in flight simulator (Study I)
In Study I, 15 pilots performed a simulated flight mission. The mean duration of
simulated flight missions was 27 minutes (range 24-30 minutes). The mean
durations of different flight phases varied from 57 s (beyond visual range
interception, phase 5) to 4 min 1 s (tactical manoeuvre, phase 4). Mean HR during
seated rest was 79 bpm (range 63-106 bpm). The highest mean HRs were measured
during tactical manoeuvring in phase 8 (97 bpm) and lowest heart rates during the
5-minute seated rest period.
A statistically significant increase in ΔHR (P < 0.005) was observed during the
entire flight mission (phases 3-15) when compared with 5 min seated rest. During
the control period (phase 16, 20-minute reading task) there was no difference in
HR when compared to seated rest.
During the flight mission, an increase in ΔHR (P=0.003) was observed between
the short reading task (phase 2) and the start of flight (phase 3). Also, an increase
in ΔHR was observed between the first beyond visual range interception of enemy
fighters (phase 5) and the tactical manoeuvre following this (phase 6) (P<0.001).
ΔHR increased and remained high during the phases 6-9 (which included tactical
manoeuvrings, another beyond visual range interception of enemy fighters and
interception of enemy aircraft formation). The highest heart rates were observed
during the tactical manoeuvre preceding interception of enemy aircraft formation
(phase 8). A significant decrease in ΔHR was observed between the interception of
enemy aircraft formation (phase 9) and break-off from combat (phase 10), P = 0.003.
Moreover, during the ILS approach and landing, the ΔHR was higher than during
the control reading task (phase 16). (Fig. 17).
77
Fig. 17. Mean HR (N=15) in different phases of simulated flight, * = statistically
significant difference between the consecutive flight phases. Flight phases presented
both for Study I and Study II.
When the experienced and less experienced pilots were compared, their ΔHR
profiles showed some differences (Fig. 18), which did not reach statistical
significance at any flight phase, probably at least partly due to small group sizes
(N=7 for experienced pilots and N=8 for less experienced pilots).
78
Fig. 18. ∆HR values in different flight phases for experienced and less experienced
pilots. BVR= beyond visual range. N=7 for experienced pilots and N=8 for less
experienced pilots.
The flight instructor gave subjects a flight performance score in different flight
phases and overall flight performance score (on a scale from 1 (poor) to 5 (excellent)
with 0.25 intervals). No significant correlations were observed between ΔHR
increments and flight phase performance in any of the flight phases (Kendall’s tau
correlation coefficients varied from -0.3 to 0.3). The overall flight performance
scores varied from 2.0 to 3.75, and the only significant correlation (correlation
coefficient 0.50, P=0.013) was observed between overall flight performance score
and F/A-18C Hornet flight experience.
79
Comment
A significant increase in HR was observed during simulated flight when compared
to seated rest. High HRs and ΔHRs were observed during the hectic phases of air
combat. A decrease in HR and ΔHR was observed after breaking off from combat
during return to base, and then another increase during ILS approach, but HR
increase during the approach and landing phases was smaller than during combat
phases. Speaking and reading aloud in the simulator, without flight tasks, did not
cause an increase in HR when compared to seated rest.
In some previous studies, HR has been shown to differentiate workload
sequences in real flight (Dussault et al. 2004) but not in the simulator (Dussault et
al. 2005) In the simulator study by Dussault et al. (2005), the pilots performed a
simulated flight which included traffic pattern flying, basic instrument flying and
landing in visual conditions. In their conclusions, Dussault et al. (2005) suggests
that HR is only sensitive at higher workload levels. Results from the current study
support this. The latter phase of the current simulated flight (return to base,
approach and instrument landing in poor weather) was similar to demanding
landings for civil pilots. During the approach and landing phases of the current
study, HR increase was significantly smaller than during the most demanding
phases. Thus, the findings in the current study support the notion that HR and ΔHR
changes are observed during high-workload situations in a flight simulator. There
is considerable variation between subjects and therefore individual ΔHR is a better
tool than total HR.
The flight performance score used in this study has been used by the FinAF on
a daily basis for analysing flight performance. The flight performance scores did
not correlate with HR increments either as an overall estimate or in different flight
phases. In previous studies (Svensson et al. 1997), the correlation between HR
changes and performance was also found to be weak. This finding is also supported
by the current study: flight performance is the final outcome of the process, and the
pilots may try hard to succeed in the mission, which increases the workload but
may not be seen in the flight performance scores. The routine flight evaluation
system of FinAF instructors tended to centralise the scores to a score of three and
ratings 1 or 5 are used rarely. Thus, this overall scaling, even though useful in daily
work, should be fragmented to smaller sub-scalings for scientific use requiring
good sensitivity. Using scalings with even number of options is one possible
solution.
80
5.1.2 Radio communication during simulated flight (Study II)
Amount of radio communication
During the simulated flight missions, the mean number of messages was 224 per
flight (range 188-299 messages per flight). During Combat 2, which was the phase
with the highest amount of radio communications, there were approximately 11
messages per minute on the radio frequency, and almost 15 messages per minute at
the peak phases.
Fig. 19. Mean number of messages per minute spoken by all speakers (pilot + wingman
+ fighter/air traffic controller) and pilot only in radio frequency in different flight phases.
N=15. Statistically significant differences between consecutive flight phases are
marked with asterisk (Repeated Measures ANOVA with Bonferroni correction).
Speech rate
Speech rate (syllables per second) was calculated for pilots. Speech rate was 5.9
syllables per second in Start, 5.6 syllables per second in Combat 1, 5.7 syllables
per second in Combat 2 and 5.9 syllables per second in Return to base. The
81
differences between flight phases were not statistically significant. The mean
speech rate expressed as Finnish words per minute for pilots was 161 per minute in
Start, 149 per minute in Combat 1, 149 per minute in Combat 2 and 146 per minute
in Return to base.
Radio communication profiles
There were differences in the communication profiles and message types spoken
by pilots in different flight phases (Fig. 20). In the less demanding phases (Start
and Return to base), acknowledging messages comprised approximately 40% of
the messages spoken by pilots. As the flight mission became more demanding
(phases Combat 1 and Combat 2), the amount of informing messages and
requesting messages increased, and the relative proportion of acknowledgements
decreased. The amount of informing messages spoken by pilots was the highest in
Combat 2. Also the amount of requesting messages increased as the flight mission
progressed from Start to Combat 1, then further increased, being the highest in
Combat 2. The changes were statistically significant in the following cases:
Informing messages: The overall difference in different flight phases was
statistically significant (Repeated measures ANOVA P=0.019). However, when
Bonferroni correction was used, the pairwise comparisons did not reach
significance. When less conservative LSD adjustment was used, a statistically
significant difference was observed between Start and Combat 2 (P=0.019) and
between Combat 2 and Return to base (P=0.018).
Commands: The difference between Combat 1 and Return to base was
statistically significant (Repeated measures ANOVA with Bonferroni correction
P=0.002).
Requesting messages: The difference between Combat 1 and Return to base
(Repeated measures ANOVA with Bonferroni correction P=0.017) and Combat 2
and Return to base (Repeated measures ANOVA with Bonferroni correction
P=0.002) was statistically significant.
Acknowledgements: The changes were statistically significant between Start
and Combat 2 (Repeated measures ANOVA with Bonferroni correction P=0.002),
Combat 1 and Combat 2 (Repeated measures ANOVA with Bonferroni correction
P=0.036) and Combat 2 and Return to base (Repeated measures ANOVA with
Bonferroni correction P<0.001). The difference between Start and Combat 1 did
not quite reach statistical significance when Bonferroni correction was used
(P=0.06).
82
Fig. 20. Mean relative proportion of message types (in percentage) spoken by the pilot
in different flight phases in Study II. N=15.
Comment
During intense air-to-air combat, especially during phase Combat 2, the amount of
messages and syllables on the frequency was high. Over 10 messages per minute
(maximum almost 15 messages per minute) on the frequency represent a challenge
for a pilot’s information-processing capacity – at the same time there is also visual
information present and air combat tasks to be executed. The speech rate exceeded
the ICAO recommendation, which is 100 English words per minute. When the
message types are analysed, fighter team’s radio communication tactics seems to
change during intense flight phases. Because the communication demand in flight
task prioritising (aviate – navigate – communicate – systems management) is only
the third most important issue, it could be expected that during difficult scenarios
the amount of radio communication would decrease. This was not observed; instead,
communication and especially informing and requesting messages increased. The
phenomena probably represent the time pressure in hectic air combat and the need
for information updates, to establish SA.
Similar radio communication tactics change has also been observed in the
FinAF during real air combat training flights (Keränen 2005). Also in these real
flight situations, the relative proportion of acknowledgements decreased. The radio
speech communication profile in real combat flights seems to be similar to the
results in the current simulator study.
83
This study demonstrates that in high mental workload situations, the
communication of a fighter team changes; from the standard radio communication
phraseology to communication in which a lot of information is shared and
requested by the pilots. The decrease in acknowledgements, which confirm that a
message has been received and understood, is remarkable.
In this study, the maximum number of speakers in the radio frequency was
three. In the real flight situations there are often more speakers on the same radio
frequency. A higher number of speakers might exacerbate the situation. On the
other hand, in real-life situations also other forms of communication (such as a data
link connection) exist, and it might ease some issues.
The language used in Study II was Finnish, which is characterized by having
longer words than other languages. This was aimed to be controlled for by
calculating the syllables instead of words to make comparability with other
languages easier, but this approach only gives an estimation when compared to
other languages. The use of the Finnish language (which was the native language
of the speakers) in this study might also result in a smaller number of
communication errors than would occur if English was used. The FinAF has
increasingly used English in military aviation communication since 2004, and it
would be interesting to repeat the study using English. There is evidence from civil
aviation (Prinzo et al. 2008) that problems in ATC communication are more
common and radio frequencies are occupied for longer when the pilots’ primary
language is not English.
The message categorisation system used was the same that was used in the
analysis of real air combat training flights (Keränen 2005). It closely resembles,
but is not completely the same as, that in the study by Svensson & Andersson
(2006). This limits the comparability of the results to other studies. In the literature,
several categorisation systems for analysing radio communication are presented,
thus illustrating the huge variability in communication analysis systems. In the
future, more tools for analysing the content of communication should be studied.
5.2
Study III: Radio speech communication problems survey
5.2.1 Background data
A total of 225 questionnaires were sent to flying squadrons. 169 pilots returned the
questionnaire, of whom 138 were fixed-wing pilots and 31 helicopter pilots. All
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respondents were male. The response rate was 75%, ranging from 61% to 100% in
different squadrons. Of the fixed-wing pilots, 67% (n=93) were fighter pilots with
the current aircraft type being the F/A-18 Hornet fighter or the BAE Hawk fighter
trainer. Of the fixed-wing pilots, 29% (n=40) were other fixed wing pilots with a
current aircraft being Valmet Vinka primary trainer, Valmet L-90 Redigo, Piper
Chieftain, Gates Learjet 35 or Fokker F27. Five of the fixed-wing pilots (4%) did
not report their current aircraft type or reported several types, and their responses
were excluded from analysis when the pilot groups were compared. Results on the
background data are shown in Table 2.
Table 2. Results for background questions in Study III. Statistical significance of the
difference between pilot groups is tested with One-Way ANOVA for questions about age
and total flight hours, and with Chi Square test for other questions.
Variable
Aviation language
Fighter pilots Other fixed wing pilots Helicopter pilots
(n=93)
(n=40)
(n=31)
English 100%
English 79%
English 100%
P
Finnish 21%
29 (22-45)
35 (22-51)
32 (22-44)
*P<0.001
Total flight hours (mean)
Age (years, range)
1063
1582
1550
*P=0.003
Frequent childhood middle ear infections
20%
13%
16%
ns
1%
0
0
ns
ns
(answered yes, %)
Current ear disease/symptoms
(answered yes, %)
Solvent exposure (answered yes, %)
0
0
0
Noise exposure (answered yes, %)
16%
21%
13%
ns
Head injury (answered yes, %)
3%
8%
7%
ns
Pressure equalising problems
13%
11%
3%
ns
19%
20%
20%
ns
16%
36%
37%
*P=0.013
Tinnitus (answered yes, %)
22%
26%
13%
ns
Hyperacusis (answered yes, %)
4%
0
0
ns
(answered yes, %)
Any hearing impairment
(answered yes, %)
Noise exposure during leisure time
(answered yes, %)
5.2.2 Prevalence of radio speech communication problems
The pilots reported radio speech communication problems to occur during 14% of
flight time (mean 14%, median 10%, range 1% - 80%). Nine fixed-wing pilots and
one helicopter pilot reported that problems take place in > 50% of total flight time.
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Fighter pilots reported problems more often (15%) than helicopter pilots (12%) or
other fixed-wing pilots (9%), P<0.01 (Conover’s test). The flight type with most
problems varied depending on pilot group (Fig. 21).
Fig. 21. Flight types with most communication problems for different pilot groups.
Fighter pilots differed statistically significantly from other fixed-wing pilots (Fishers
exact test p<0.001) and from helicopter pilots (p=0.009). Fighter pilots N=87, other fixedwing pilots N=36, helicopter pilots N=28.
The pilots were asked if non-standard phraseology causes communication
problems, if the communication problems are related to certain individual
speaker(s), and whether they had noticed that a strong or unusual dialect or
speaking style causes problems to radio communication. The answers are shown in
Figure 22.
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Fig. 22. Issues related to phraseology and speaking styles. Percentage of respondents
who reported each particular issue as a problem. N=93 for fighter pilots, N=40 for other
fixed-wing pilots and N=31 for helicopter pilots.
5.2.3 Speech rate and speech characteristics
Questions about speech rates (ATC, fighter controller, other aviators) and speech
characteristics were asked on an ordinal scale (with options being
never/rarely/quite often/almost always). The results are shown in Figure 23. The
most significant problem was many speakers on the frequency causing overlapping
speech, especially for fighter pilots.
87
88
many speakers / overlapping messages’, the difference between pilot groups was statistically significant (Kruskal Wallis P <0.001).
Fig. 23. Speech rate and speech communication related issues in different pilot groups. Other FW= other fixed-wing pilots. For ‘Too
The controllers’ gender does not appear to have a major effect on radio speech
intelligibility, since 87% of the pilots reported no difference in male/female speech
intelligibility. Of the remaining 13%, 11.4% considered male controller speech to
be harder to understand, and 1.2% answered that the speech of female controllers
is harder to understand.
Not enough speech?
Pilots seem to judge the amount of radio speech communication as sufficient and
do not appear to perceive situations in which there is not enough communication,
or where there are overly short messages or call signs, as a problem (Fig. 24).
Fig. 24. The occurrence of issues related to inadequate amount of speech. Other FW =
other fixed-wing pilots.
5.2.4 Background noise
Background noise was a relatively common problem (Fig. 25). Helicopter pilots
complained about background noise slightly more often than other pilot groups, but
the difference was not statistically significant.
89
Fig. 25. How often does background noise effect on radio communication according to
different pilot groups in Study III.
Physical issues in flight environment, technical systems, synthetic speech
Questions considering the effect of G-forces and anti-G manoeuvres, positive
pressure breathing and F/A-18C Hornet radio were only relevant to fighter pilots.
These issues are reported in Figure 26.
Technical difficulties in systems used for ground communication (while the
aircraft is on the ground) were very common among fighter pilots: of them, 83%
had experienced problems in them. They detail overall poor audibility, background
noise and problems in situations when many aircraft were simultaneously online.
Also 56% of other fixed-wing pilots had experienced the ground communication
problems.
90
Fig. 26. How often physical issues related to flight environment and technical systems
have an effect on radio speech communication. Responses are only from fighter pilots.
Synthetic speech produced by the aircraft (e.g. voice alarms) appears to be
functional and the pilots are satisfied with the systems, since none of the 96 pilots
(of whom 74 were fighter pilots, 16 other fixed-wing pilots and 6 helicopter pilots)
reported having encountered problems with synthetic speech systems.
Hearing protection and hearing protection attitudes
The willingness to use developed hearing protectors (e.g. custom-made systems or
active noise reduction systems) was high: of all pilots, 93% would use such systems
if they were available. Fighter pilots and helicopter pilots reported willingness to
use enhanced hearing protection slightly more often (96% of fighter pilots and 94%
of helicopter pilots) than other fixed-wing pilots (85%), but the difference was not
statistically significant.
5.2.5 Radio speech communication related incidents and dangerous
situations
Thirty-one pilots (18% of the respondents; 24 fighter pilots, 6 fixed-wing pilots, 1
helicopter pilot) stated that they had encountered a near-miss/dangerous situation,
in which radio speech communication had played a role, during their military flying
career. Altogether 34 incident reports were received. No accidents were reported.
91
In addition to these 31 pilots, 6 pilots reported that such an incident had happened
but did not go into any further detail.
The reports clustered around missing a message during high-workload
situation (8 reports), not hearing the message (6 reports) and problems with read
back/hear back (6 reports). Other types and situations of different seriousness levels
were also reported. Logistic regression analysis did not indicate an association
between any of the background factors (age, total flight hours, flight hours with
F/A-18C Hornet or BAE Hawk, reported hearing impairments) or the number of
reported communication problems and these incidents.
Open questions
Of all the pilots, 85% wrote comments and opinions in the questionnaire. The issues
most commented on were the use of non-standard phraseology (31 comments),
fatigue and its effects on communication (24 comments) and insufficient noise
protection (15 comments).
5.2.6 Comment
The estimated frequency of radio speech communication problems (14% of flight
time) can be considered high, even though it is a subjective estimate. This survey
revealed that the major issues are overlapping speech, especially during air combat
training exercises, non-standard phraseology and background noise, especially
during helicopter operations.
Problems in radio communication appear to have been associated with nearmiss/dangerous situations: 18% of the pilots had experienced such an event they
considered to have affected flight safety during their career. Most of the reports
were from fighter pilots, who have the biggest information load and time pressure
during their missions. In some of the incident reports, a risk of mid-air collision
with friendly aircraft was possible according to the pilots.
These results emphasise the importance of understanding the role of radio
communication as delivering the time-critical information during demanding
situations. Radio communication and auditory channels are the fastest way to
deliver new or changing information, but they are also vulnerable, as the occurrence
of overlapping speech and missing acknowledgements demonstrate. The
importance of planning communications with the recipients’ situation in mind
should be remembered. In addition, communication training should help the
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speakers to understand the differences between everyday communication and radio
communication. The speakers should be aware that the communication strategies
in everyday environments are subconscious. In radio speech they need to be
intentionally replaced by strategies such as signalling the recipient and
acknowledging a message. This is important not only for the current situation at
hand but for longer-term team SA.
Missing acknowledgements were an often-reported problem in this survey.
During field studies (Keränen 2005) and also in a flight simulator (this thesis, Study
II) it has been shown that acknowledgements decrease during the most intense
flight scenarios when the radio band is overloaded by speech. The answers to open
questions in this survey reveal that ignoring acknowledgements can be intentional
during these situations. This issue has received only little attention in the past, and
needs to be taken into account in future communication training. Whole teams
should understand that there are limitations in working memory and informationprocessing capacity. Therefore, teams should focus on transmitting the critical
information if the recipient is already at the limits of his/her capacity - excessive
information further burdens the operator. Moreover, the problems that arise with
this ‘coping strategy’ should be known. Because the capacity of working memory
is limited, postponing a reply may result in forgetting the message completely.
Pilots’ responses to open questions revealed some issues that should be noted
and studied further. They reported that tactical phraseology changes rapidly, and
delays in trainings and implementing new versions has, according to the pilots,
resulted in different phraseology versions being in use. This may lead to
misunderstandings. Non-standard phraseology and plain English are sometimes
used when there is no correct saying in the phraseology, or it is not remembered.
This is inevitable, but it should be understood that when plain English is used, the
interpretation of the message is more diverse and depends largely on the English
skills of both the speaker and the receiver. This should be taken into account in
training: in situations when there is no designated saying in the phraseology, the
risk of misunderstandings is increased. As the use of English (i.e. the non-native
language of Finnish pilots) is nowadays routine, this issue should be emphasised.
According to the results, situations in where there is not enough speech
communication or the messages are too short are not perceived as a problem at all.
However, according to a recent accident analysis (Puolustusvoimat 2014), an
insufficient or inadequate amount of speech communication has been at least a
contributory factor in a recent mid-air collision accident. It is possible that the idea
93
of too little communication has not been understood as a flight safety issue, and it
should be studied further.
5.3
Study IV: moulded communication earplugs survey
5.3.1 Background data
A total of 146 pilots responded to the survey: 127 fixed-wing pilots and 19
helicopter pilots. The response rate was 59%. The mean age of the respondents was
32 (range 23-51). The results for background questions are presented in Table 3 and
Table 4.
Table 3. Background data of pilots who responded to the survey in Study IV.
Variable
Male
response
N
100%
146
Worked in the Finnish Defence Forces
Mean 11 years (1-29)
142
Flight duty percentage of working time
Mean 63% (0-100%)
145
Mean 1254 (180-3600)
143
Finnish
99%
145
Swedish
1%
1
English
96%
140
Finnish
4%
6
Active squadron/battalion pilot
85%
121
Staff/headquarters pilot
11%
16
Other
4%
6
Fighter
78%
108
Transport/primary trainer
9%
12
Helicopter
13%
19
Total flight hours
Native language
Aviation language
Current task
Current aircraft type
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Table 4. Current and previous ear and hearing problems reported by pilots in Study IV.
Variable
Yes
No
Any current hearing problems1)
23%
77%
Current leisure-time noise exposure1)
20%
80%
Current pressure equalising problems1)
11%
89%
Current tinnitus1)
27%
73%
Current hyperacusis2)
8%
92%
Previous recurrent middle ear infections in childhood1)
21%
79%
Previous solvent exposure1)
1%
99%
Previous noise exposure3)
7%
93%
Previous hospital treatment because of any head trauma1)
4%
96%
Any previous hearing deficit1)
10%
90%
Previous noise exposure during leisure time1)
25%
75%
1)
N=146
2)
N=145
3)
N=142
In the background questions, older pilots reported current hearing problems more
than younger pilots. The prevalence of any current hearing problems was 13% with
pilots between 20 and 29, 24% with pilots aged 30-39, and 44% in the 40-49 age
group. The difference between the age groups was statistically significant (Chisquare test P=0.01). There was no difference between the age groups in current
leisure-time noise exposure, pressure equalizing problems, tinnitus or hyperacusis.
Current hearing protection during flight duties
The most commonly used hearing protection was the combination of flight helmet
and m-CEP (49% of the pilots) (Fig. 27). The pilots who had reported ‘several’
usually explained that they use different solutions in different aircraft/mission types
(e.g. helmet only in some aircraft and headset in others).
95
Fig. 27. Currently used hearing protectors during flight duties. N= 146.
5.3.2 m-CEPs: usage rates, positive issues, negative issues
For hearing protection, m-CEPs had been used or tried by 93% (136) of the
respondents. They were currently in use by 62% of the pilots (63% of the fixedwing pilots and 53% of the helicopter pilots). The mean duration of m-CEP use was
2 years 9 months (range 2 months – 4 years 6 months). The pilots who were
currently using m-CEPs used them often; 90% of flights on average (range 5-100%).
Positive aspects of m-CEPs
Of the pilots who had used or tried m-CEPs, 93% would recommend them to their
colleagues. m-CEPs were also usually considered to be better than the hearing
protectors pilots had used previously (Fig. 28).
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Fig. 28. Pilots’ opinion about m-CEPs compared to other hearing protectors. m-CEP vs.
Helmet alone N=132, m-CEP vs. ear plugs N=115, m-CEP vs. headset N=90.
The experienced speech intelligibility was better with m-CEPs: Of the pilots who
had used or tried m-CEPs, 85% reported an improvement in experienced speech
intelligibility under difficult hearing circumstances. Helicopter pilots appear to
experience this improvement slightly more often, since 100% of the helicopter
pilots and 83.5% of the fixed-wing pilots reported an improvement. However, the
difference between the groups did not reach statistical significance (Chi-square test
P=0.08). There was no difference in the reported speech intelligibility improvement
between pilots with and without current hearing problems (Chi-square test P=0.88),
or between pilots in different age groups (Chi-square test P=0.23). m-CEPs may
also have a preventive effect on post-flight tinnitus: 30% of the 115 pilots who
answered the question about change in occurrence of tinnitus after starting use of
m-CEPs reported a decrease in post-flight tinnitus. None of the pilots reported an
increase in post-flight tinnitus, and no change or no tinnitus at all was reported by
70% of the pilots. There was no difference in the effects of m-CEPs on post-flight
tinnitus between pilots who reported current hearing problem and those who did
not (Chi-square test P=0.49), or between the different age groups (Chi-square test
P=0.31).
97
Negative aspects of m-CEPs
Of the pilots who had used or tried m-CEPs, 82% reported that they had
encountered problems with the system, and only 18% reported no problems with
the device. Technical and discomfort issues were the most common problems. Of
the pilots who had used or tried m-CEPs, 58% reported having experienced some
discomfort issues (discomfort in outer ear, ear canal, hot spots or too loose/poor
fitting, or several of them) and 42% had not experienced discomfort issues. A more
detailed division of the problems related to m-CEPs is presented in Figure 29.
Fig. 29. Most common problems associated with m-CEPs, % of pilots who had used or
tried m-CEPs and reported each issue, N=135. One pilot was allowed to select several
options.
Of the pilots who responded, 38% (56 pilots) were currently not using m-CEPs.
These non-users were asked for their reasons for not using the device. The most
common reasons were discomfort issues and devices being faulty or undergoing
maintenance (Fig. 30).
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Fig. 30. Distribution of reasons for not using m-CEPs (responses from pilots who were
currently not using m-CEPs), N=55.
Pilots were also asked to report if they had experienced technical problems in the
wiring of the system, problems with maintenance of the device, blocking of the
pressure equalisation vent or broken ear moulds. Of the pilots who had used or tried
m-CEPs, 46% had experienced technical problems with wirings and 43% with
maintenance of the device. Problems with pressure equalisation vent were rare;
only 5% reported that the vent had been blocked. The number of damaged or broken
ear moulds was zero for 46% of the users, one for 37%, two for 14% and three or
more for 3% of users.
Incidents and dangerous situations related to m-CEP use
The pilots were asked to report any incidents, near-misses and in-flight
physiological incidents associated with m-CEP use. A total of 9 incidents or nearmisses were reported (by 7% of pilots who had used or tried m-CEPs). In seven of
these cases a malfunction or a disturbance with the m-CEP signal had caused radio
communication to be inaudible, at least momentarily. One incident involved an
attempt to adjust the m-CEP fitting, which caused the pilot to use a wrong switch.
Two in-flight physiological incidents were reported: one incidence of ear pain (vent
99
malfunction) and one external ear canal barotrauma associated with a hooded
immersion suit.
5.3.3 Radio communication issues in general
The mean prevalence of perceived in-flight communication problems (as an
estimate of problems as a percentage of flight time) was reported to be 14% (range
0-100%, median 10%). The flight type during which the subjects experienced most
communication problems varied depending on the pilot group. For 53% of the
fixed-wing pilots (57% of fighter pilots and 40% of other fixed-wing pilots) this
was air combat training flights, while 53% of the helicopter pilots encountered most
problems during basic training flights. The responses about the effect of
background noise on radio communication are shown in Figure 31.
Fig. 31. How often background noise affects communication in Study IV (responses of
different pilot groups).
5.3.4 Comment
Study IV shows that m-CEPs offer many benefits in military aviation and the pilots
have noticed these advantages. Almost all of the pilots who have used or tried them
would recommend them to their fellow pilots. Of those pilots who have experience
of the device, 85% reported that it had a positive effect on hearing in difficult
100
listening conditions. m-CEPs were also considered to be more functional than
hearing protectors they had previously used.
Despite the positive aspects, complaints and problems were common. Even
though the m-CEP plug is custom-moulded to fit each user’s ear canal, discomfort
issues were, along with technical problems, the main reason for not using the device.
Technical reliability of the device also caused problems, because the mean use time
was less than three years and already at the time of the survey, several devices were
faulty or in maintenance. One reason behind this could be that pilots themselves
are responsible for everyday maintenance of the device. Even though many pilots
reported treating the device delicately, this may be a factor behind the high failure
rate. In addition, the delivery times of new m-CEPs as replacements for the broken
devices were excessively long.
Previously, pilots suffering hearing loss have reported to benefitting from CEP
use (Ribera et al. 2004) and the use of hearing protection devices that aid hearing
instead of passive headsets (Casto & Casali 2013). In the current study, pilots with
and without current hearing problems and/or tinnitus both reported an improvement
in speech intelligibility equally. Also, 30% of subjects reported a decrease in postflight tinnitus, and this may indicate an improvement in noise protection. Better
radio speech intelligibility is important because it can have a positive effect on an
operations and flight safety.
However, some sounds such as synthetic voice alerts are communicated via
loudspeakers in the cockpit, not via m-CEP. The reduction in these sounds and its
effects on either pilots with normal hearing or those with hearing impairments was
not studied in this survey. Because this may be a flight safety issue, this should be
studied further.
Discomfort issues remain a common complaint about m-CEPs. However, in
the current study it appears that with the custom-moulded plug the discomfort
issues are less common when compared to previous studies conducted with
standard CEPs. In the current study, 58% of the pilots reported having experienced
some discomfort issues, while Koda et al. (2009) reported that 78% of the pilots
have reported discomfort. The results from Koda are, obviously, from a different
study setting and from a different m-CEP and aircraft types, and therefore one has
to be careful with comparisons, but still the smaller amount of discomfort issues in
the current study seems promising.
One issue worth studying further is the plug material: the plug in the current
study is made of silicone, which has been reported to sometimes cause irritation in
the ear canal (Pascoe 2013). Longer flight durations are also likely to increase the
101
number of complaints about discomfort. Nowadays, m-CEPs made of medical
polyurethane (Miliears CEP ®) are also available in the FDF. In the future, it might
be useful to study and test new m-CEP materials in order to reduce irritation.
Because discomfort issues were a common reason for not using m-CEPs, the usage
of the systems would probably increase with improvements in the custom fitting of
the device. Another very important issue in reducing discomfort issues related to
m-CEPs is to readjust flight helmet fitting. This is often overlooked.
In the survey, two in-flight psychophysiological incidents were reported: one
incidence of ear pain due to vent malfunction, and one ear canal barotrauma. These
are rare but still possible complications with m-CEPs, and a possible flight safety
issue because they can cause severe pain which distracts pilots from their flight
duties. One of the cases was caused by a pressure vent malfunction, and the other
case was the result of an immersion suit hood blocking the ear. Even though the
problem is rare, it emphasises the need for a well-functioning vent in the m-CEP,
especially during sorties that include rapid altitude changes.
The reported prevalence of any current hearing problems varied from 13% to
44%, depending on the age group, in this study. In a population- based sample study
conducted in Finland (Uimonen et al. 1999), a better-ear hearing level worse than
20dB was observed in 2% of the 35 year-olds, and in 6.6% of the 45 year-olds. In
United Kingdom, approximately 30% of the adult population have been reported
to have unilateral hearing levels greater than 24dB (average of frequencies 0.5, 1,
2 and 4 kHz), and 26% of adults report hearing problems in noise (Davis &
Moorjani 2003). The self-reported number of hearing problems in the current study
is higher than the prevalence of objectively-measured hearing losses by Uimonen
et al (1999). It is, however, in line with the number of self-reported hearing
problems by Davis & Moorjani (2003). The previous research in the FinAF
(Kuronen et al. 2004a) has shown that Finnish military pilots generally have good
hearing levels in audiometric tests. Nevertheless, in the current study, they report
hearing problems. This emphasises the importance of functioning communication
and hearing protection systems in the working environment.
Hyperacusis was reported to be surprisingly common – by 8% of the pilots
(N=12). Ten of these pilots reported their current aircraft type, and it was either an
F/A-18C Hornet fighter or a BAE Hawk fighter trainer for all but one of them, and
also the pilot currently not flying fighters had previously flown them. Age and total
flight hours were similar among pilots with and without current hyperacusis. Even
though conclusions cannot be drawn from this finding due to the small sample size,
this finding should be studied further: it is possible that high aerodynamic noise
102
exposure in fighter aircraft may be one factor behind hyperacusis. In a study by
Raynal et al. (2006), fighter and helicopter pilots have been reported to be at
increased risk of hearing loss, and the occurrence of hyperacusis may be an
indicator of this risk. More studies on hyperacusis and related risk factors among
pilots should be carried out in the future.
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104
6
General discussion and recommendations
6.1
Flight simulator studies
In the flight simulator (Studies I-II) an increase in HR was observed during a
simulated flight, the highest heart rates being at high intensity combat flight phases.
HR differentiated between flight phases with different mental workload levels. HR
analysis can reflect a fighter pilot’s ability to maintain high performance levels
during periods of elevated task demand. Speaking itself did not cause HR changes,
and physical factors that could cause HR changes, such as G-forces, were not
present in a simulator. Due to individual differences in HRs, the recommendation
to use each subject as his/her own control is repeated also after this study. The daily
flight performance score used in the FinAF by flight instructors for analysing pilot
performance is not the best choice for scientific use, because the instructors tend to
centralise the scores near to an average score. ECG-based HR analysis is a cheap
and highly valid method for mental workload analysis in a flight simulator.
Considerable changes in radio communication were observed when flight
phases with different workload levels were compared in Study II. The amount of
communication increased as the flight phase became more intense, and the speech
rate exceeded the 100 English words per minute level recommended by the ICAO.
The highest message frequencies were above 10 messages per minute and the
maximum was almost 15 messages per minute. This is a challenge for information
processing because the pilots are required to also gather information via visual
channel, and to execute various other tasks. When message types were analysed,
the communication tactics of the team appeared to change. The pilots are trained to
prioritise their actions so that aviation tasks are the first priority, and it could be
expected that during difficult scenarios communication decreases. This did not
happen; instead, the amount of informing and requesting messages increased and
the acknowledgements decreased. This finding is consistent with findings in real
civil aviation high workload situations (Silberstein & Dietrich 2003), where a
substantial decrease in communication coherence was observed during high
workload.
The observed change in fighter team communication, from the standard radio
communication phraseology to communication in which a lot of information is
shared and requested by the pilots, was an interesting finding. Also the decrease in
acknowledgements, which confirm that a message has been received and
105
understood, was remarkable. A decrease in acknowledgements has previously been
noted in real air combat training flights (Keränen 2005). There are two possible
explanations for this change in communication:
1.
2.
It may indicate that the pilots need information delivered at an individual pace
or in different forms, depending on the level of mental workload. The pilot may
ask for information as he/she needs it, and this could explain the increase in
messages that ask for information.
It could be a coping strategy, as declining acknowledgements and read backs
allow more information to be delivered in the same radio frequency band
during time-critical air combat phase.
The responses to survey study (Study III) also support this: some respondents
indicate in the open questions that they use repeat requests and skip
acknowledgements intentionally, as they plan to focus on the situation at hand and
then request a repeat when the workload situation is better. This may indicate that
the standard phraseology is unintuitive in high-workload situations. However, this
approach has some dangers: working memory capacity is limited, and therefore it
is not guaranteed that the pilot will remember to ask for a repetition later. Also, the
lack and/or inconsistent use of acknowledgements multiplies the risk. If
acknowledgements are used inconsistently, the sender of the message (e.g. the
fighter controller) cannot tell whether the missing acknowledgement was due to not
hearing or just that it will be asked again. Therefore, the fighter controllers’ ability
to ‘back up’ this postponement of information decreases. Missing
acknowledgements lead to controllers repeating the unacknowledged information,
further increasing the amount of speech and information load of all the speakers on
the frequency.
The simulator was effective for studying mental workload and the related
communication changes. Simulators are increasingly used in aviation for training
purposes. The current findings about the changes in communication and workload
in the flight simulator and their comparability to observations in real flights support
simulator use in communication research as well as in communication training.
Up until now, the focus of communication training has been in phraseology
training. In the future, the focus of communication training should be expanded
beyond training only phraseology towards training that takes the variation between
different situations and information needs better into account. The team members
should get more training about the communicational demands of the other team
members in situations with different intensity. Communications should be planned
106
‘from receiver’s point of view’, and training communication in teams might be
beneficial to achieve this goal.
The observed change in radio communication during the most intense
situations is probably of interest to Army and Navy, who also use radio
communication during their assignments. Similar changes in radio communication
are likely to also occur in their scenarios with high workload. The Army and Navy
personnel, as well as personnel in several civilian professions might, therefore,
benefit from understanding the changes in radio communication during a high
workload.
6.2
Survey studies
In the survey studies, the total estimated amount of radio speech communication
problems accounted for 14% of the flight time, air combat training exercises being
the flight type with most problems. Major issues are overlapping speech, especially
during air combat training exercises, non-standard phraseology and background
noise, especially during helicopter operations.
The estimated frequency of radio communication problems was 14% of flight
time in both studies, which can be considered quite high, even though it is a
subjective estimate and there was great variability between the respondents. The
survey studies were done with an interval of 5 years between them (2007 and 2012)
and the estimation about radio communication problem frequency remained the
same during this period. The use of the English language in practically all aviation
radio communication was somewhat new in 2007, but at the time of the second
survey in 2012 it was routine. Therefore, the similar figures in the amount of
communication problems can be considered as a positive thing, because it indicates
that communication problems have not increased when the pilots started to use a
non-native language. Military pilots in Finland are required to take the English
language proficiency test of Civil Aviation Authority, and to pass the test and to
achieve categories 4-6 (on a scale of 1-6). Category 4 means an operational level
of English language proficiency, 5 is extended and 6 is expert or nearly native
speaker. Therefore, there is a considerable difference in English language
understanding and comprehension between levels 4 and 6.
The pilots reported a need and motivation to use enhanced hearing protection
in the survey conducted in 2007. Survey studies also revealed that the major radio
communication problems include multiple speakers on the same radio frequency
band causing overlapping speech, missing acknowledgements, high background
107
noise, especially during helicopter operations, and technical problems. The use of
a data link for information transfer could ease this issue, especially with non-urgent
information.
Leisure-time noise exposure was reported by 16% of fighter pilots, 36% of
other fixed-wing pilots and 37% for helicopter pilots (if calculated for all pilot
groups together, the leisure-time noise was reported by 24% of all pilots) in Study
III. Five years later, leisure-time noise exposure was reported to be 20% (study IV).
These figures are in line with a study carried out previously in Finland with
conscripts (Jokitulppo et al. 2008). The significance of recreational noise as a threat
to hearing is increasing (Holma 2015). The current study has focused on radio
communication-related issues in operational environments, but the importance and
knowledge about risks related to any kind of hearing impairment, regardless of the
cause of it, should be emphasised to pilots.
After the first survey 2007, the m-CEP was introduced to daily work. In the
survey conducted in 2012, m-CEPs were shown to be a promising tool for
improving hearing protection and communication in difficult hearing
circumstances in military aviation. However, even with the very high-quality mCEP system, the number of technical issues and discomfort issues were high. These
have later been addressed by improvements in helmet fitting, as well as providing
pilots with another type of m-CEP (Miliears CEP®). Technical reliability and
durability of the m-CEP system is obviously very important. In the demanding
working environment of military aviation, technical problems with the
communication system can have serious consequences. Also, to get the full benefit
of the HPDs, they must be worn continuously when exposed to noise, and this is
not possible if the HPD is faulty. In the future, careful fitting of the m-CEP is critical
for reducing discomfort, and new studies with different m-CEP materials should
carried out in order to evaluate whether discomfort and irritation issues could be
resolved. Experiences from hearing-aid fittings could be utilised with these matters.
6.3
Reliability of the results
6.3.1 Strengths of the study
This study provides comprehensive information about the different aspects of
military aviation radio speech communication collected both experimentally in
flight simulator studies, and from a larger pilot population via survey studies.
108
Information was gathered from all age groups of pilots on active duty. All flying
squadrons of the FinAF and the FDF were represented. This study provided new
information about radio communication and hearing protection especially from
fighter pilots working conditions. A good overall picture about radio
communication-related issues is achieved. The use of a flight simulator in this study
made the exclusion of physical factors in a real flight environment possible and
allowed workload-related issues to be focused on. The use of a simulator was
shown to be appropriate in studying pilot workload and radio communication. In
survey studies, a large proportion of Finnish military pilots was reached. The goal,
which was to enable the pilots to give their responses about radio communicationrelated issues freely in an anonymous study, was achieved.
6.3.2 Limitations of the study
The limitations of the simulator studies (I-II) include the low number of subjects
(15 pilots). In Study II, the fact that there is no universally adapted categorisation
system available for aviation radio communication research is a challenge. The
categorisation used in the current study was selected because it has been used
earlier in FinAF in research during real flights, to enable a comparison of the
communication patterns in real and simulated flight. The language used in the
simulator studies was Finnish, and after this study the use of English in Finnish
military aviation has increased substantially. Because the pilots used their native
language in the current study, Study II may underestimate the communication
problems, compared to today’s circumstances. The low number of subjects may
also have influenced the results, since individual speaking habits could have had an
effect. The cognitive load analysis used in Study II was performed post-trial and no
reliability measurements were conducted for this analysis.
Limitations of the survey studies (III-IV) include the fact that they were
anonymous, and therefore e.g. the audiometric results and other parameters, such
as medical histories or official incident reports, cannot be correlated with the results.
The response rate, even though it can be considered relatively good in both surveys,
represent only a sample of all pilots. The response rate of the m-CEP survey (Study
IV) was 59%, which is lower than in Study III. One possibility for this difference
is that pilots who have no experience of m-CEPs did not reply. The helicopter pilot
subgroup was small in both surveys. Survey studies are subjective in nature, and
this needs to be taken into account when the results are interpreted. A recall bias is
possible with retrospective survey studies. In both surveys, questions about the
109
amount of communication problems and other issues are, due to the nature of
survey studies, estimates of the prevalence of the problem. In the incident reports
in the survey studies, the pilots themselves decided whether some occurrence in
their career was ‘worth reporting’ in their opinion. Because of this, the amount of
incidents is probably an underestimation. If a pilot does not judge an occurrence in
flight as an incident, or more dangerously, does not even realise anything is unusual,
the incident goes unreported. Some of the incidents here have been studied
officially, some have not, but due to anonymity, the official incident reports and the
reports in the surveys could not be compared.
In Study III, the other fixed-wing pilot group was heterogeneous: it included
both beginner pilots in early stages of their careers, and very experienced pilots
flying the same aircraft types. Certain questions, e.g. the effect of pressure
breathing and G-forces, were only relevant to fighter pilots. Two questions were
excluded from the analysis: a question about the use of additional hearing
protection, and a sub-question in which the pilots were asked to divide perceived
problems into predefined categories. These questions were not clear enough and
they had been interpreted differently by different subjects.
In Study IV, only one type of m-CEP was available to the pilots at the time of
the survey, so m-CEPs from different manufacturers could not be compared. Some
other hearing protection solutions (such as certain ANR systems) have been shown
to function in fighter environments, but due to their unavailability in Finland they
could not be compared to m-CEPs. A question considering the use of additional
hearing protection was not clear enough and was understood differently by different
subjects and was therefore excluded.
6.4
Generalizability of the results
The findings of this study about the effect of high cognitive workload on radio
communication can be generalised to Finnish military pilots working in these
aviation environments. They can also be used to estimate the possible cognitive
workload- related issues in other military branches and professions using radio
communication. In civil aviation, instrument approaches are similar to the latter
part of the simulated flight mission in this study, and the results can also be
generalised to these scenarios. In the simulator study, the Finnish language was
used and therefore the findings and the changes in radio communication while
using Finnish may be an underestimation when compared to the current situation
in which English is used for aviation radio communication by non-native English
110
speakers. The communication profiles in the simulator were similar to those of real
flights and they can therefore be generalised to real military aviation scenarios.
In survey studies, large proportion of Finnish military pilots were represented.
The results from the survey study concerning m-CEPs in military aviation
environments are well generalizable to military pilots operating with similar
aircraft generations. Findings related to usability issues, discomfort issues and the
reasons for not using m-CEPs can also be used in personnel in the Army and Navy,
as well as in civilian sector, who need hearing protection during their duties.
6.5
Future research and recommendations
This study raised several questions that could be the subject of further studies in
the future.
In simulator studies, the overall flight performance scaling, even though useful
in daily work, should be fragmented to smaller sub-scalings for scientific use
requiring good sensitivity.
Communication training should be improved in the future, in order to enhance
pilot-fighter controller team SA. Increasing team communication training with the
whole pilot-controller team, e.g. in an air combat simulator, should be considered
and studied. The radio speech communication profile in real combat flights is
similar to the results in the current study, indicating that a flight simulator can be
used for fighter pilot communication research. More research and standardisation
is needed on systems used for communication categorising in scientific use.
In survey studies, it was observed that the situations in which there is not
enough radio communication were reported very rarely. This can be a signal that
these situations have not been understood as a possible safety issue. The issue
deserves to be noticed: an inadequate amount of radio communication has been a
contributory factor in a military aviation accident in Finland. The awareness about
the issue seems to be increasing: for example, the recent version of HFACS takes
it more into consideration (DoD HFACS 2015).
In the future, issues arising from the survey results, such as the benefit of the
m-CEPs both for pilots with and without hearing problems could be analysed with
non-anonymous studies. They should include hearing tests and more in-depth
analysis of current hearing issues, and their relation to m-CEPs and other HPDs.
The reported radio communication problem rates did not change between the
two surveys conducted with five-year intervals (Studies III and IV) even though
the use of English became routine and the new hearing protection systems were
111
adopted. Therefore, from a flight safety perspective this issue should be controlled,
by conducting another survey for example, and analysing incident reports.
In Study IV, it was found that new m-CEP-type hearing protectors were
approved by pilots and they consider them functional in their working environment.
Still, discomfort issues and technical problems remain common. Therefore, m-CEP
development should continue and include new materials in addition to siliconbased material as well as improvements on the endurance of the device. The
insertion techniques of m-CEPs, the effect of individual training in fitting the
system and helmet, and their effect on user satisfaction could be studied. For
analysing the effect of improved hearing protection on the endpoint – hearing
impairments – a long-term follow-up should be continued in the FDF occupational
health units.
In the field of HF, the currently used analysing tools and systems focus on
errors and mistakes at different levels of the organisation (Nodeland 2016). This
also applies to HFACS, which is widely used in military aviation and also in this
study. However, in the field of HF research there may be a change in the climate in
the near future: away from analysing errors towards the positive issues. That is, the
protective factors and resilience mechanisms that increase human performance as
the working environments become more complex and harder to understand. For
example, the creator of the original Swiss Cheese model has recently written a book
titled ‘The human contribution – unsafe acts, accidents and heroic recoveries’
(Reason 2008). Successful situations are expected things which do not catch
attention – in our minds, there is nothing remarkable in a flight that landed safely.
Therefore, it is obviously much easier to study negative events and incidents, than
to discover what went right in a situation that went perfectly.
Some attempts to include this positive perspective already exist: For example,
a ‘New HF tool’ that includes the positive aspects has been used in the Finnish air
traffic management organisation Finavia and described by Teperi et al. (2015). In
the tools used in military aviation, such as the newest HFACS version (DoD
HFACS 2015) this has not yet been utilised. In the future, these positive factors and
resilience mechanisms should be investigated – it is definitely worth knowing why
and how we succeed.
112
Recommendations for future research, development and training
Research tools:
–
–
For analysing pilot performance, scalings which are fragmented into smaller
subscalings should be developed for scientific research.
For analysing the content of radio communication, categorisation systems
should be developed.
Training: the following issues should be introduced into training
–
–
–
The importance of flight helmet re-fitting with the use of m-CEPs
The importance of hearing protection, both in work-related noise and leisuretime noise, should be included in basic flight training
The radio communication training should include issues related to team
communication. Training should be expanded from training phraseology,
towards team communication training and factors associated with functional
radio communication.
Hearing protectors
–
–
New m-CEP materials should be studied, in order to alleviate the discomfort
issues.
The technical development of m-CEPs should be continued, to assure the
technical reliability, as well as the best possible comfort.
Research
–
–
–
–
The equal benefit of the m-CEPs, both for pilots with and without hearing
problems, should be analysed with non-anonymous studies.
The prevalence of radio communication problems and related incidents need
to be controlled
For analysing the effect of improved hearing protection on the endpoint,
hearing impairments, a long-term follow-up should be continued in FDF
occupational health units.
In the field of HF, the positive factors and resilience mechanisms related to
human performance should be investigated.
113
114
7
Conclusions; the findings of this study in the
HFACS framework
The purpose of research in the field of aerospace medicine is to improve human
performance and flight safety at the organisational level. Better radio speech
communication will improve flight safety and operational effectiveness from a
human factors point of view. At the level of an individual pilot, the goal is to
improve work-related health and reduce occupational health risks in a profession
which has several inherent risks. In this thesis, a number of radio communicationrelated issues were studied and addressed.
In Study I, fighter pilot workload and pilot mental workload changes were
studied in a flight simulator. Heart rate was shown to reflect the level of mental
workload. The task load of simulated air combat correlated with HR changes.
In Study II, the effects of different mental workload levels on radio
communication were studied. During intense flight phases, the amount of radio
communication increased remarkably, and changes in the content of
communication emerged, as the amount of informing and requesting messages
increased and the amount of acknowledging messages decreased. The
communication strategy of military pilots changed during hectic air combat.
Communication training that focuses on team communication should be introduced
for pilots and fighter controllers.
In Study III, the type and occurrence of radio communication problems were
studied by means of a survey study. Communication problems were reported to
occur on 14% of flight time, on average. The most prevalent problems included
multiple speakers on the same radio frequency band causing overlapping speech,
missing acknowledgements, high background noise especially during helicopter
operations, and radio technical problems. The pilots reported a high motivation to
use enhanced hearing protection.
In Study IV, advantages, benefits and problems associated with moulded
communication ear plugs were studied with a survey study. m-CEPs offer many
benefits in military aviation, almost all pilots would recommend them to other
pilots and they appear to have a positive effect on hearing in difficult listening
conditions in military aviation. However, discomfort issues and technical problems
remain. Better helmet fitting after the m-CEP update and new m-CEP materials that
are less irritating may improve these issues.
115
The most important findings of this thesis are presented here within the Human
Factors Analysis and Classification System (HFACS) framework, in order to
understand their relevance as flight safety factors. The findings are numbered and
presented in HFACS levels in Figure 32, page 117.
1.
2.
3.
4.
5.
6.
7.
116
Teamwork and violations: Not following the phraseology or postponing a reply
can sometimes be intentional coping strategies, in order to reduce mental
workload (Studies II & III).
Physical environment: background noise was reported to be a common
problem, with the highest figures among helicopter pilots (Study III). Pilots
reported a need and motivation for enhanced hearing protection (Study III).
Technological environment: not hearing the message because of technical
problems with radio systems and hearing protection devices (Studies III & IV).
The major reasons for not using m-CEPs were technical issues and discomfort.
Of the pilots who have used or tried m-CEPs, 56% had experienced problems
with the system’s cable connector and disturbances in the signal, and 58% had
experienced discomfort problems (Study IV).
Mental awareness: mental workload was high in the most intense flight phases
(Studies I-II).
Physical problem: the pilots have hearing problems: the self-reported amount
of current hearing problems varied between 13 and 44% depending on pilot
age group, and 8% reported hyperacusis (Studies III- IV).
Teamwork: the standard radio phraseology pattern tended to change during
high-workload situations (Study II). Speech rates in a simulator were higher
than instructed (Study II). Overlapping speech was reported to occur quite
often by 45% and almost always by 2% of fighter pilots (Study III). Situations
with too little radio communication were reported to be very rare, which could
indicate that the possibility of an inadequate amount of communication may
not be understood as a flight safety factor (Study III).
Resource problems: long delivery times and technical problems in hearing
protection devices. One-third of the pilots who were not using m-CEPs did not
use them because the device was faulty or in maintenance (Studies III & IV).
Fig. 32. Findings of this thesis presented within the Human Factors Analysis and
Classification System (HFACS) framework. The stars represent the position of each
finding of this study at different tiers of the HFACS, in order to understand their
relevance as possible flight safety factors.
117
In the future, in the heavily visual environment of military aviation, hearing and
hearing protection should be remembered. Hearing and efficient radio
communication have substantial effects on mission effectiveness and flight safety,
since time-critical information is verbally communicated via radio. Effective
hearing protection is also an economic issue, since, for example, NIHL remains the
most common occupational disease in Finland (Oksa et al. 2015). Since military
aviation working environments include challenging scenarios for hearing
protection, their details need to be further studied in these environments. Functional
hearing protection and reduced noise levels can also help in keeping the volume of
communications at the lowest practical level, which further reduces the overall
noise exposure. This is important, because communications represent a remarkable
proportion of the overall noise.
Currently, most of the aircraft used in military aviation are 4th generation or
enhanced 4th generation fighters, and the studies in this thesis were conducted in
this environment. In the near future, the 4th generation fighters will give way to the
5th fighter generation, of which the first are currently entering service and most of
them are in the test phases. With these fighters, some new issues related to human
factors need to be taken into consideration. They include a whole new level of
sensory fusion (visual, auditive and tactile cues presented at the same time), 3D
audio, ANR techniques, wearable technology, automated emergency procedures
based on physiological (eg. pilot’s oxygen saturation) or aircraft data (e.g. cabin
pressure) and also new opportunities for information transfer (Newman 2014b,
Rice et al. 2016). Understanding and studying pilot performance within the
changing operative environment remains important. Radio communication and
understanding the different aspects of auditory situation awareness, and the role of
hearing conservation in it, are also important for soldiers in the Army and the Navy
as well as to personnel in the civil sector who also use radio communication in their
operations.
118
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130
Appendix 1: Items in Radio speech
communication in military aviation - survey
(Study III)
Background information questions
Task
Response alternatives
pilot / navigator / air traffic controller /
fighter controller / operator
Gender
male / female
Age
Years
Mother tongue
report, if you are multilingual report also
other languages
How long have you worked in the Finnish Defence Forces
Years
Current squadron
Name
Aviation language
Finnish / English / other
Flight training received in English
report trainings
English phraseology courses attended
list courses
Aircraft types for which you have type training
list aircraft types
Total flight hours and flight hours in different aircraft types
Report
Flight hours during last 12 m / 3 m / 1 m
Report
Flight duty percentage of working time
%
Current aircraft type
Report
Recurrent otitis in childhood
no / yes (if yes, report how many times)
Current ear disease
no / yes (if yes, report what)
Solvent exposure
no / yes (if yes, report what)
Noise exposure
no / yes
Hospital treatment because of any head trauma
no / yes (if yes, report year and diagnosis)
Noise-induced hearing loss
no / yes
Other hearing loss diagnosed by doctor
no / yes
Leisure time noise exposure
no / yes
Problems in pressure equalising
no / yes
Tinnitus
no / yes
Hyperacusis
no / yes
131
Study Questions
response alternatives
Speech communication problems in my work
How often does radio speech communication problems occur in
% of flight time
your opinion
Flight type with most communication problems
Basic training flights / training flights / air
combat exercises / transport flights
Are communication problems related to (a) certain single
no / yes
speaker(s)
Does the dialect of a speaker affect speech communication
no / yes
Does non-standard use of phraseology cause problems in
no /yes
communication
How often is the amount of speech information insufficient
never / rarely / quite often / almost always
How often do G-forces and anti-G straining methods affect
never / rarely / quite often / almost always
speech communication
How often does positive pressure breathing affect speech
never / rarely / quite often / almost always
communication
How often does background noise affect speech communication
never / rarely / quite often / almost always
How often do problems with the F-18 Hornet radio and/or mask
never / rarely / quite often / almost always
microphone occur?
Speech rate and speech characteristics
How often do ATC controller use overly fast speech rate
never / rarely / quite often / almost always
Hof often fighter controller uses overly fast speech rate
never / rarely / quite often / almost always
How often other aviators use overly fast speech rate
never / rarely / quite often / almost always
How often are there too many speakers and overlapping
never / rarely / quite often / almost always
messages on the same radio band?
How often are acknowledgements left out
never / rarely / quite often / almost always
How often are messages and call signs too short
never / rarely / quite often / almost always
How often do mistakes in read back/hear back take place
never / rarely / quite often / almost always
Too-close / dangerous / accident situations, fatigue
How many incidents, hazardous situations and accidents (in
Report number and explain the situations
which radio speech communication failures have had a role)
have you had during your entire military career
How often does fatigue and reduced attention due to fatigue
every day /once a week / once a month /
cause you to miss messages?
once a year / less than once a year / never
Other issues
Have you had problems with the ground communication system
between the cabin and ground personnel
132
no / yes
Other issues
Do you have problems with synthetic speech produced by the
no / yes
aircraft
The effect of the speakers gender on speech intelligibility (is it
male / female / no difference
harder to understand if speaker is…?)
Would you use custom-made ear canal or active hearing
no / yes
protectors if they were available
133
134
Appendix 2: Survey items in Moulded
communication earplugs in military aviation survey (Study IV)
Background information
(1) Gender
(2) Age
(3) Native language and aviation language
(4) How long have you worked in the Finnish Defence Forces
(5) Current squadron/battalion
(6) Current task (active pilot / headquarters / other)
(7) Flight duty percentage of working time
(8) Current aircraft type
(9) Aircraft types for which you have type training
(10) Flight hours (total and on different aircraft types) and during last 12m, 3m, 1m
(11) Current hearing and ear-nose-throat problems: Do you currently have…
(11a) Problems with hearing
(11b) Hearing impairment
(11c) Ear disease
(11d) Noise exposure during leisure time
(11e) Problems in ear pressure equalisation
(11f) Tinnitus
(11g) Hyperacusis
(11h) Leisure-time noise exposure
(11i) Do you use hearing protection during leisure time (how often? percentage of exposure time)
(12) Previous hearing and ear-nose-throat problems: Have you previously had…
(12a) Recurrent otitis in childhood (how many times?)
(12b) Solvent exposure
(12c) Noise exposure
(12d) Hospital treatment because of any head trauma
(12e) Any previous hearing deficit
(12f) Noise exposure during leisure time
(12g) Have you used hearing protection during leisure time noise exposures (how often?
percentages of exposure time)
135
Radio communication issues in general
(13) How often do you experience problems in aviation radio communication (percentage of flight time)
(14) Radio speech communication problems occur most often in which flight types (basic training flights
/ training flights / air combat training flights / transport flights / other)
(15) How often does background noise affect radio communication (never / rarely / quite often / almost
always)
(16) What hearing protection do you usually use when flying (headset only / flight helmet only / flight
helmet + ear plugs / flight helmet + m-CEP / other)
(17) How often do you use hearing protection when working in a noisy environment (never / rarely /
quite often / almost always)
Questions considering m-CEPs
(18) Do you use m-CEPs (if not, why?)
(19) How often do you use m-CEPs (percentage of flights)
(20) How long have you used m-CEPs
(21) Have you had any problems with m-CEPs (Yes/No). If yes, report all problems you have
experienced from the list below:
Poor fitting - helmet causes pressure
Poor fitting - discomfort or pain in outer ear
Poor fitting - discomfort or pain inside ear canal
Poor fitting - the plug feels loose or does not stay in place
Problems with pressure equalisation while using m-CEP
Problems with wiring or connectors
Other (describe)
(22) Have you experienced that m-CEP use has been a factor in incidents or hazardous situations
(Yes/No, if yes, describe the situation)
(23) Have you experienced physiological incidents because of m-CEP (Yes/No, if yes describe the
situation)
(24) Does m-CEP improve speech intelligibility in difficult hearing situations (Yes/No)
(25) Have you noticed any change in the occurrence of tinnitus after you began using m-CEP (tinnitus
has decreased / no change or I don't have tinnitus / increased)
(26) Have you had problems in maintenance of m-CEPs (Yes/No)
(27) Has the pressure equalisation valve in your m-CEPs got blocked in use (Yes/No)
(28) How many ear pieces have sustained damage or failure during your m-CEP use
(29) Have you experienced technical problems in the wiring or cables of m-CEP and helmet (Yes/No)
136
(30) Would you recommend m-CEPs to your fellow airmen or subordinates? (Yes/No)
(31) When comparing m-CEP to other hearing protection devices, do you find m-CEP
Better / equal / worse than flight helmet only
Better / equal / worse than conventional ear plugs only
Better / equal / worse than headset only
137
138
List of original publications
I
Lahtinen TMM, Koskelo JP, Laitinen T, Leino TK: Heart rate and performance during
combat missions in a flight simulator. Aviat Space Environ Med 78: 387–391.
II Lahtinen TMM, Huttunen KH, Keränen HI, Sorri MJ, Leino TK: Radio speech
communication during simulated air combat missions. Manuscript.
III Lahtinen TMM, Huttunen KH, Kuronen PO, Sorri MJ, Leino TK. Radio speech
communication problems reported in a survey of military pilots. Aviat Space Environ
Med 81: 1123–1237.
IV Lahtinen TMM, Leino TK: Molded Communication Earplugs in Military Aviation.
Aerosp Med and Hum Perform 86: 808–814.
Articles reprinted with the permission of the Aviation, Space and Environmental
Medicine and Aerospace Medicine and Human Performance journals.
Original articles are not included in the electronical version of this thesis.
139
140
ACTA UNIVERSITATIS OULUENSIS
SERIES D MEDICA
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Book orders:
Granum: Virtual book store
http://granum.uta.fi/granum/
D 1398
OULU 2016
UNIVERSITY OF OUL U P.O. Box 8000 FI-90014 UNIVERSITY OF OULU FINLA ND
U N I V E R S I TAT I S
O U L U E N S I S
ACTA
A C TA
D 1398
ACTA
U N I V E R S I T AT I S O U L U E N S I S
Taija Lahtinen
University Lecturer Santeri Palviainen
Postdoctoral research fellow Sanna Taskila
Professor Olli Vuolteenaho
Taija Lahtinen
Professor Esa Hohtola
RADIO SPEECH
COMMUNICATION
AND WORKLOAD IN
MILITARY AVIATION
A HUMAN FACTORS PERSPECTIVE
University Lecturer Veli-Matti Ulvinen
Director Sinikka Eskelinen
Professor Jari Juga
University Lecturer Anu Soikkeli
Professor Olli Vuolteenaho
Publications Editor Kirsti Nurkkala
ISBN 978-952-62-1427-6 (Paperback)
ISBN 978-952-62-1428-3 (PDF)
ISSN 0355-3221 (Print)
ISSN 1796-2234 (Online)
UNIVERSITY OF OULU GRADUATE SCHOOL;
UNIVERSITY OF OULU,
FACULTY OF MEDICINE;
FINNISH DEFENCE FORCES,
CENTRE FOR MILITARY MEDICINE
D
MEDICA
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