Select Committee on Science and Technology First Report

CHAPTER 3: research since 2000

The scope of research

3.1.  Our original report recommended that the Government commission research into a number of priority matters. In their response the Government announced that they had commissioned the Institute for Environment and Health (IEH) to conduct a consultation exercise to confirm independently the concerns identified by our inquiry and to investigate any other potential issues and gaps in knowledge with a view to promoting or facilitating further research. Stage 1 of the study into Possible Effects on Health of Aircraft Cabin Environments[15] was published in January 2001. It identified five main areas where more research was needed: DVT, air quality (physical and chemical aspects), transmission of infection, cosmic radiation and jet lag.

3.2.  Stage 2 of this study was published in June 2001 and the AHWG considered the report at its meeting on 27 July of that year[16]. The Stage 2 report investigated the current stage of knowledge on each of the five issues identified in Stage 1 and pointed out shortfalls. The results are summarised in Box 2. We welcome this clear and helpful statement of the main research priorities, against which subsequent research activity must be considered. Below we summarise the main research projects that have since taken place.


Summary of prioritised research needs

High Priority


  • Improved case-control studies (with particular attention to the selection of controls).
  • Prospective studies, based on measurements prior to symptoms becoming apparent.
  • Interaction of DVT risk with hypoxia and exercise.


  • Investigate the key CAQ parameters in flight: the blood oxygen saturation of crew members and passengers, pressures and rates of change, temperature, air movement, humidity, ventilation rate and concentrations of common pollutants and organophosphates, self-reported health and comfort.


  • Inclusion of jet lag as a confounding effect in studies of DVT, CAQ and infection risk.

Medium Priority


  • Experimental biomedical research, on the possible effects of decreased cabin pressure, low partial pressure of oxygen, stress.


  • As for high priority recommendation, but for occupied aircraft on the ground.
  • Laboratory/simulation studies of the CAQ parameters, the effects of interactions.
  • Intervention trials on the impact of altering parameters that correlate with health outcomes (e.g. humidification, gas phase air filters, reduced temperature).
  • Measurement of exposure to insecticides and organophosphates.


  • The incidence of the infectious agents of TB should be determined in the air, and on furnishings and filters on flights from countries where TB is endemic.


  • Exposure monitoring of cabin and flight crews.
  • Further development of biological markers for cancer risk.

Low Priority


  • Co-ordinated case studies to clarify estimates of the incidence of recent travel in DVT patients (if possible, in association with case-control studies).


  • A survey of air filter condition and maintenance (this would also be relevant to transmission of infection).


  • The effect on the movement of pathogens of adjustable air supply nozzles.
  • Cosmic radiation
  • A large epidemiological study on the magnitude of risk, including discrimination of skin cancers risks from CR and UV exposure.


  • Desk study of the short-term and long-term health and safety implications of jet lag, and the economic implications.

Anthropometric Study to Update Minimum Aircraft Seating Standards

3.3.  This study was commissioned by the CAA on behalf of the JAA and published in September 2001[17]. At the time of our original report this study was under way and we recommended that "it be completed urgently"[18]. The study reviewed the UK CAA Airworthiness Notice 64 (AN64), published in 1989, which regulates the minimum seat space dimensions for all UK-registered aircraft over 5,700 kg which carry 20 passengers or more. The United Kingdom is the only country in the world to have regulations on seat spacing.

3.4.  The study also took account of the increase in size of people over time. It stated that AN64 "is based on data for 5th percentile to 95th percentile range of passenger sizes, which means that at least 10 percent of passengers will not be accounted for". It went on to say that "it is widely recognised that where safety is concerned the range should be increased to cover the 1st percentile to 99th percentile range."

3.5.  The study also stated that, as a result of the continuing increase in the average size of the European population since AN64 was published in 1989 (an increase that may accelerate with the projected rise in obesity described in the recent Foresight report[19]), it would, by 2001, only have accommodated up to 77th percentile of the population. It recommended that the regulatory minimum distance between seats[20] be increased to a minimum of 28.2 inches or ideally to at least 29.4 inches to include the 1st percentile to 99th percentile range of the population. It also found that "the current requirement does not provide enough space for taller passengers to adopt the 'brace' position" calling for the ability of passengers to adopt the brace position to be considered as one of the criteria for determining acceptable seat space. We return to the issue of seat spacing in Chapter 4 below.

Cabin Air Quality

3.6.  We have already drawn attention to Stage 2 of the study into Possible Effects on Health of Aircraft Cabin Environments of 2001, which identified cabin air quality as a high priority area for research. In 2001, following a small number of reported contaminated air events when flight crew were partially incapacitated, the CAA commissioned a research project into Cabin Air Quality[21]. The study comprised two phases. Phase 1 was a toxicological review of pyrolysed oil by-products[22]; this concluded that "no single component or set of components can be identified which at conceivable concentrations would definitely cause the symptoms reported in cabin air quality incidents". However, short chain organic acids, such as pentanoic and valeric acid, were found. Although these acids can act as irritants, there is no information available on the concentrations needed to cause irritancy.

3.7.  Phase 2 of the study was an analysis of contaminated cabin air supply ducts removed from two BAe 146 aircraft. The ducts were found to be "contaminated with carbonaceous material containing chemicals entirely consistent with the pyrolysis products of aircraft engine oil." Again, short chain organic acids were also found together with some additional compounds such as the ortho isomer of tricresyl phosphate (TOCP). However, "toxicological review of these previously unrecorded chemicals [TOCP] indicates that they are most unlikely to be present in sufficient concentration to have a physiological effect and, in any case, the specified symptoms were not the same as those associated with exposure to TOCP".

3.8.  As a result of this study, published in 2004, the CAA required operators and manufacturers of particular aircraft types to make a number of changes to minimise oil leaks into the bleed air. According to the report, service records show that "these actions have controlled any airworthiness risk by reducing both the number and severity of reported events". We return to the issue of "contaminated air" in Chapter 4 below.

Study of Air Quality in the Aircraft Cabin

3.9.  The Study of Air Quality in the Aircraft Cabin[23] was published in October 2003. It was commissioned by the AHWG and conducted by the Building Research Establishment (BRE) as an extension of the CabinAir project (detailed below), to include measurements on older aircraft types, the BAe 146 and the Boeing 737-300. Fourteen flights were monitored measuring air quality parameters with the aim of determining whether the cabin air quality in these older aircraft was in any way an issue, and whether they differed significantly from newer types of aircraft. The study found that all measured air pollutants on board the flights were always below recommended health limits, when these applied. Comparisons with the CabinAir study have not taken place yet but early results suggest that there are no obvious differences in the cabin environment between older and new aircraft.

Extent of Aspirin Use for the Prophylaxis of DVT on Long Haul Flights

3.10.  In 2004 Synovate Healthcare were commissioned by the AHWG to carry out a study aimed at quantifying the extent of aspirin usage amongst UK long-haul aircraft passengers, in order to assist discussions in the AHWG and to facilitate the development of public health policy regarding DVT. A total of 1,672 face-to-face interviews were conducted between 8 September and 29 November 2004. These showed that of the total sample analysed, 20 percent had taken or planned to take aspirin before, during or after their long haul flight[24]. We return to this issue in paragraphs 4.15-4.17 below.

WRIGHT Project

3.11.  At the time of our original inquiry DVT was the one health issue above all others that seemed to concern the flying public. It was also identified as a priority research area in Stage 2 of the Possible Effects on Health of Aircraft Cabin Environments. The AHWG decided soon after its creation, at the end of 2001, that supporting and funding the World Health Organization (WHO) Research Into Global Hazards of Travel (WRIGHT) project, would be the best way to fill the research gap on DVT[25]. Dr Bill Maton-Howarth of the DH said at the AHWG meeting on 11 January 2001 that "the WHO study remained the best match for the objectives of the UK AHWG"[26].

3.12.  The aim of the WRIGHT project was "to confirm that the risk of venous thromboembolism (VTE) is increased by air travel and to determine the magnitude of risk, the effect of other factors on the risk and to study the effect of preventive measures on risk"[27]. In the event, the study on preventive measures was deferred to Phase II.

3.13.  The project consisted of three epidemiological studies and two physiological studies. Some 1,800 patients referred to six anticoagulation clinics following a first VTE were evaluated in the Netherlands; a study was carried out among frequent flyers employed at major international companies; and questionnaires were sent to all members of the Dutch Airline Pilots Association. The physiological studies included a study on the effects of a hypobaric (low pressure) chamber on 73 healthy volunteers with no risk factors. A further study assessed 71 healthy volunteers with risk factors before, during and after an eight-hour commercial flight.

3.14.  The final report of Phase I was published on 28 June 2007. The main findings were:

  • Travelling for more than four hours in any form of transport approximately doubled the risk of VTE;
  • The absolute risk of VTE for a flight of more than four hours was 1 in 6,000 passengers, rising to about 1 in 1,000 passengers for longer journeys and multiple flights;
  • The longer the flight, including multiple trips, the greater the risk of developing VTE;
  • There was no difference in the relative risk of VTE if the cabin pressure was reduced;
  • Those who were very short, very tall or overweight were at slightly greater risk;
  • Travelling by air accentuated other pre-existing VTE risk factors, for example use of oral contraceptives and the presence of prothrombotic blood abnormalities; and
  • "Hyper-responders" seemed to react to unspecified flight-related factors: if an individual had a risk factor the likelihood of him developing VTE increased dramatically after an eight hour flight.


3.15.  This EU-led project is being carried out by the Building Research Establishment (BRE). CabinAir "is one of the largest and most important studies to be carried out on the environment in aircraft cabins"[28]. It has looked into health and comfort issues involved in cabin air quality in commercial aircraft. The results of the study are likely to be published within the next few months.

Health Effects of Aircraft Cabin Environment (HEACE)

3.16.  This study is EU-led, with BRE as the United Kingdom partner. It aims to understand the impact of the aircraft environment on health and comfort of flight and cabin crew and comprises ground testing in cabin simulators and in-flight monitoring. Although HEACE was scheduled to run for three years, from November 2001 to October 2004, it was prolonged until April 2005. The report has not yet been published.

Ideal Cabin Environment (ICE)

3.17.  The Ideal Cabin Environment (ICE) project is an EU-led study aiming to address concerns about the combined effects of cabin environmental parameters on the health and well-being of passengers in commercial aircraft. Dr Ray Johnston, head of the AHU, is the Medical Chair of the Project; he told us that the study "is unique in its approach, looking at health and well-being" (Q 270). Some 1,500 people took part, 50 percent male and 50 percent female, encompassing three age groups (18-34, 35-50 and 50 years plus), and some individuals with cardiac and respiratory diseases. Environmental conditions were examined, including a range of cabin altitudes, as well as psychological well-being. The ultimate aim of the project is "to set a new European standard once the data are analysed" (Q 270). The study will report in the autumn of 2008.

Friendly Aircraft Cabin Environment (FACE)

3.18.  The aim of FACE is to improve cabin and cockpit comfort in the next generation of civil transport aircraft. FACE will address the environmental comfort parameters that depend on noise, vibration and air quality technology. The project is EU-led with a budget of approximately 35 million Euros and has 30 European partners. The results have not yet been published.

Mortality and Cancer Rates

3.19.  The CAA together with the London School of Hygiene and Tropical Medicine are undertaking a study comparing mortality and cancer rates of pilots, air transport control officers and the general population. The project began in 1997 and preliminary results are being compiled for publication.

United Kingdom research capacity

3.20.  It is clear that our original report stimulated considerable research into aviation health. Many, though not all, of the priority areas, have been or are being addressed. However, the projects we have described are all international, and we remain concerned at the amount and quality of research being undertaken in the United Kingdom.

3.21.  Professor Michael Bagshaw, Aviation Medicine Director at King's College London, told us that "there is insufficient research" into aviation health in the United Kingdom. He added that "the only substantive research we have had has been from the WRIGHT study from the WHO and the research that has been done on cabin air quality … is pan-European, as opposed to UK-led" and in practice very little of the research is being done in the United Kingdom. He went on to say "there is very little input from Her Majesty's Government into research in the United Kingdom and I believe that this is a pity". Although, as far as we are aware, Professor Bagshaw is the only academic in this country at professorial level wholly specialising in aviation medicine, he commented that he was unable himself to conduct any research: "My university does not fund research in civil aviation medicine and there is no source of funding." (Q 113)

3.22.  More generally, we note that many of the international research projects described above, some of which were set up as much as ten years ago, have yet to report. In some cases these are long-term studies, so delays in publication are to a degree excusable. In other cases, however, the complications inherent in pulling together research teams across international boundaries may also have played a part in creating delays. This is frustrating—there can be little doubt that a more intense, UK-based research effort, with Research Council support, would have produced results more quickly as well as building up expertise across the country.

Gaps in research

3.23.  There remain gaps in research. In 2000 we recommended an "exploration of the ways different aspects of the aircraft cabin environment may interact, particularly on those in less than average health"[29]. This recommendation is even more relevant today. Phase I of the WRIGHT Project found that "the more pronounced risk increase observed after air travel compared to ground travel for some of these risk factors may suggest an effect of flight-related factors, which are absent during travel by other modes of transport"[30]. We expect that the ICE Project may address some of the issues, but it is imperative that we find what these "flight-related factors" are and what effects they have on passengers and in particular on those with existing medical conditions. For instance, the Anthropometric Study to Update Minimum Aircraft Seating Standards recommended that "studies investigate any specific relationships between seating parameters and thromboembolic disease"[31]. No such studies have taken place. It is essential that the WRIGHT Project addresses this issue.

3.24.  We also recommended in 2000 that researchers should be enabled to extract "maximum value from available and improved medical records of aircrew concerning any long-term effects from exposure to the aircraft cabin environment"[32]. The CAA's study into mortality and cancer rates is a good start and we will follow with interest the publication of the preliminary results. However, we heard at our seminar of the difficulties that the CAA encountered in carrying out this study. Section 23 of the Civil Aviation Act 1982 restricts the CAA on how they can use information from pilots' medical examinations for research purposes. When we put this issue to Jim Fitzpatrick MP he told us that the Government "have not made judgment on it yet" but that it is "something that we are prepared to consider in due course".

3.25.  Stage 2 of the Study of possible effects on health of aircraft cabin environments highlighted jet lag as a high priority area in need of research, and in particular the inclusion of jet lag as a confounding effect in the study of DVT, cabin air quality and infection risk. Also highlighted was the need to study the long-term effects of jet lag—the physiological condition resulting from alterations to the circadian rhythm (the body's internal clock) due to transmeridian travel—and shift working patterns on air crew. Such issues are increasingly relevant today given the expansion of long haul flights. But to our knowledge little has been done in this area.

3.26.  At its meeting on 6 October 2006 the AHWG decided not to support a research proposal from Dr Jane Zuckerman from the Royal Free Hospital to carry out research into the transmission of respiratory infections by or in air travel. However the Group agreed that "there were potential issues, which good quality research could tease out"[33]. It is interesting to note how the travelling public have come to accept that at times they may contract a cold after a flight and this is assumed to be a "side effect" of air travel. Written evidence submitted to the original inquiry included personal accounts from passengers complaining of contracting respiratory infections following a flight. We concluded in 2000 that the re-circulation of air in aircraft does not in fact aid infection transmission. However, given the public's perception on this issue it is worth investigating specifically whether any aspect of the flying experience, such as jet lag or psychological factors, makes us more susceptible to contracting respiratory diseases.


3.27.  We recommend that the Government fully support Phase II of the WRIGHT Project including investigations on flight-related factors which may increase the risk of VTE, the relationship between seating and VTE, and effective preventive measures.

3.28.  We recommend that the Government bring forward an amendment to Section 23 of the Civil Aviation Act 1982 which regulates the use of information from air crew medical records, so that anonymised data can be extracted and used to carry out epidemiological research projects.

3.29.  We recommend that jet lag should be studied as a confounding effect of DVT as part of Phase II of the WRIGHT Project. Other research projects, such as FACE should include jet lag in their studies. We also recommend that the CAA, as the body responsible for the health and safety of air crew while on board an aircraft, commission a study into the possible long-term health effects that jet lag may have on air crew.

3.30.  We recommend that in addition to contributing to international research projects, the Government and the Research Councils explore ways to increase the research capacity in aviation health that exists within the United Kingdom. A strong research base in this country is essential if awareness and understanding of aviation health are to be increased across the wider medical profession.

3.31.  We find surprising and frustrating the number of EU-led research projects that have not published their reports. We recommend the Government should take an interest in these projects and if possible expedite the publication of their results.

15   See Back

16   Minutes of AHWG 27 July 2001 Back

17   See Back

18   op. cit. Science and Technology Committee Air Travel and Health 2000, paragraph 3.51. Back

19   See Back

20   The distance between the seat back cushion to the back of the seat in front Back

21   See Back

22   Oil heated to very high temperatures similar to those in an aircraft engine. Back

23   See Back

24   See Back

25   We remind readers that we use the term DVT in this report as it is the initial deep vein thrombosis that may be related to the aircraft cabin environment. Venous thromboembolism (VTE) is a complication which occasionally arises from DVT and this term is used both in the WRIGHT project and in some of our evidence. Back

26   AHWG Minutes 11 January 2002 Back

27   See Back

28   See Back

29   op. cit. Science and Technology Committee Air Travel and Health 2000, paragraph 9.3. Back

30   See Back

31   See Back

32   op. cit. Science and Technology Committee Air Travel and Health 2000, paragraph 9.3.  Back

33   AHWG Minutes 6 October 2006. Back

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