The Airline Pilots Forum and Resource
The Airline Pilots Forum and Resource

Flight Safety and Contaminated Air

Source: Aviation Contaminated Air Reference Manual

Flight Safety Aspects of Contaminated Air ©
by Susan Michaelis

It is important to note that exposure to contaminated air is exposure to a mixture of chemicals, some of these chemicals have neurotoxic and or immunotoxic properties. Contaminated air has the capability to seriously impair crew performance and has done so on many occasions as we will detail in this chapter. Therefore, the important questions that need to be asked are: How will the pilots know that the air is contaminated and what can they do about it? What can the pilots do to stop all on board the aircraft being exposed to contaminated air? Do pilots rely on their sense of smell or do they have contaminated air detection systems in the cockpit?

As a modern commercial jet airliner is worth tens of millions of dollars and many contaminants within contaminated air, such as carbon monoxide have no smell, it must be safe to assume that all aircraft have some form of contaminated air detection system, especially as the ‘bleed air’ is not filtered. However the answer is no. There are no contaminated air detection systems fitted to any commercial jet or turboprop aircraft except for a crew’s ability to smell. While airline pilots are required to undergo regular medical checks to be able to fly, these checks only look at a select number of areas. These tests do not review a pilot’s sense of smell and, in fact, pilots do not need to have a sense of smell to hold a medical certificate to fly. Some pilots and cabin crew have no sense of smell at all, while others are partially insensitive to smell. Another major concern is that after 3 minutes of exposure to an odorant, the subject’s perceived intensity of the odorant is reduced by about 75%. [1]

The airline industry is facing an ongoing serious health and flight safety problem whereby:

  • Engine oils and hydraulic fluid sometimes contaminate the air supply;

  • These contaminants may contain neurotoxins, sensitizers and various volatile organic compounds, as well as organophosphates such as Tricresyl Phosphate (TCP), Triphenyl Phosphate (TPP) or Tributyl Phosphate (TBP);

  • Contaminated air is known to have impaired crew performance and on occasion incapacitated pilots and flight attendants;

  • The air is not filtered and there are no contaminated air detection systems apart from the pilots, who are not tested or even required to have a sense of smell.

This unacceptable situation has been ongoing for over forty years. This chapter will look at the flight safety debate in great detail, how crews frequently see contaminated air as normal, how the industry has dealt with contaminated air and its impact on flight safety, the aircraft checklists that deal with contaminated air and the impact of contaminated air on a crew’s ability to fly the aircraft.

Contaminated Air Seen as Normal

Despite the fact that pilots would have received years of training before flying commercial jet or turbine aircraft most crews are oblivious to the medical effects of contaminated air exposure. Crews will go to work and may notice the brief or longer contaminated air smell and mostly think nothing of it. If the smell becomes more intense they might start to pay attention, but for most crews to actually take action they would be waiting for some form of visible sign of contaminated air which would be an extremely serious exposure event. Most crews also continue to see contaminated air as a nuisance and are unaware of the serious flight safety issue contaminated air can cause and has caused on many occasions. This point was clearly expressed by British Aerospace in 2001:

" Incidents have been reported involving impaired performance of the flight crew... In the past, oil leaks and cabin/flight deck odours and fumes may have come to be regarded as a nuisance rather than a potential flight safety issue. However, whilst investigations are being carried out, oil leaks and cabin/flight deck odours must be regarded as a potential threat to flight safety, they should not be dismissed as a mere nuisance and should be addressed as soon as possible." [2]

Other references are made to the very important fact that fumes / contaminated air events have been seen as routine or non events. The Canadian Transport Safety Bureau advised, when reporting on the 1998 fatal accident of Swissair 111 that, ‘within the aviation industry there has been belief that smoke or odour situations are often a non event, thus further diminishing concern about minor odour events.’ [3] Many crews have reported contaminated air as a normal part of flying and experience contaminated air more often than not at various stages during most flights. [4] An Australian Transport Safety Bureau (ATSB) occurrence report on a contaminated air event on a BAe 146 in 2002 noted that the difficulty in generally locating the source of the oil leaks that caused the fumes and that, ‘the failure of oil seals has been a common factor in the majority of those incidents.’ [5] The ATSB also advised that, ‘The aircraft type has been the subject of recurring fume incidents throughout its operating life… Because of this history, the fume events may have become `routine’ in the thinking of some operating crew and awareness of the possible risks may have diminished as a result.’ [6] Another example of this routine thinking and acceptance that the oil fumes were routine and acceptable is shown in an Australian BAe 146 incident report in which the outgoing pilots in a crew change advised the oncoming new pilots verbally that the air was contaminated. The oncoming pilots noted the air was contaminated, departed anyway and then experienced adverse effects. [7] In fact, East West (an Australian airline) BAe 146 pilots in the early 1990s were making passenger announcements on all flights apologising for the, ‘sweaty socks’ smell. [8]

Flight Safety or Occupational Health and Safety?

Areas of conflicting information on the safety or health aspects of contaminated air are numerous. A few such examples include the Aerospace Medical Association who recognized as far back as 1983 that, ‘smoke fumes in the cockpit is not a rare event and is a clear threat to flight safety because of acute toxic effects’ and ‘that all of the toxic substances (including engine oil and hydraulic fluids) have acute and long term effects.’ [9] A British Aerospace (BAe) internal complaint report regarding a Dan Air (UK airline) BAe 146 in 1991 reported contaminated air and adverse effects experienced by crews. The report requested a definitive statement on the medical implications of fumes / smells in the cabin, with crews reporting headaches and nausea. The 1993 update to the report notes that despite a two year wait there is, ‘still no statement on health and safety’ with a hastened answer requested. [10] One airline operator advised that while the oil fumes are not medically harmful, they can cause irritation of the nose, throat, eyes and can cause headaches and as such could be very distracting. The airline therefore stated that it can, ‘in some circumstances cause a flight safety hazard.’ [11] The same airline two years later advised that, ‘BAe146 cabin air quality is not a safety of flight matter. The aircraft meets all the regulatory and OH and S standards.’ [12]

It is clear that there are conflicting messages being sent to crews about whether aircraft contaminated air is a health and aviation safety issue. One of the main aviation regulators, CASA, advised that, ‘Oil fumes are more of a health problem than an aircraft technical defect, as not all pilots are affected and there is no mandate to look at health.’ [13] CASA clearly stated that contaminated air was outside its area of responsibility by stating, ‘Toxins in cabin air are an OH and S issue and not responsibility of the Aviation Regulator which is responsible for short and medium term effects on safety.’ [14] CASA incorrectly advised in 2002 that there had been no requirement to report oil fume events to CASA, it then changed its mind and correctly advised in 2004 that all oil fume events were reportable as major aircraft defects. [15][16]

Many in the aviation industry clearly view contaminated air in general as being outside its responsibility and expertise and not an air safety issue. Some additional comments made supporting this view include the following: In 1999 British Aerospace advised that this issue was outside the industry’s expertise by way of a statement, ‘The regulatory bodies as admitted by CASA yesterday, are not competent to rule on such a highly specialised area. Neither are the airlines or the manufacturers.’ [17] BAe also advised, ‘With the weight of human evidence and suffering, which is quite clear, there must be something there. We are comfortable on the one hand that there is no flight safety risk.’ [17] The American FAA advised in 2005 that of 4360 fume/smoke events connected to the engine /APU, all but 3 were viewed as not a serious threat to flight safety or of immediate serious harm to crew or passengers, as the fumes were noticeable with no reported immediate effects or caused minor impairment or injury only to crew and or passengers. [18]

As can be seen in more detail in Chapter 15, ‘Regulations to Protect Us’ there is significant overlap between health and safety responsibility. This overlap was highlighted during the 1999-2000 Australian Senate investigation into the BAe 146 problems. This overlap is allowing aviation regulators and occupational health and safety regulators to debate whose responsibility contaminated air actually is. This results globally in both the flight safety problem and the occupational health issues to remain unresolved and inadequately addressed. Examples of this failure to accept responsibility include the UK CAA advising that it is not responsible for general or long term health apart from effects impacting on a pilot’s fitness to operate that flight and not responsible for cabin crew health or passenger health or comfort at all, as its prime responsibility is for flight safety. [19] The UK HSE, on the other hand, stated it has no active responsibility towards the health of air crew or passengers. [19]

Complacency and Denial

Contaminated air like hypoxia can subtly affect the crew member. Many crews have become impaired, partially incapacitated or incapacitated without knowing it. Pilots are checked once or twice a year depending on age, by specialist aviation doctors to ensure they are medically fit to fly. However, as noted before, a pilot’s ability to detect contaminated air currently depends upon them having a good sense of smell despite this never being checked. With little to no education on what contaminated air is, nor recognition that these fume events are in fact aircraft defects, safety hazards and able to cause serious adverse effects, crews invariably just assume this regular odour is part of the flying environment. This results in passengers usually being told nothing.

Pilots and cabin crew have been taught about hypoxia but they have never been properly told to take contaminated air seriously. In fact, they are actually told from a health viewpoint that there is essentially nothing to worry about in the short term and definitely no long term health effects. This advice and misinformation comes despite the fact it has been acknowledged that nobody actually knows what concentrations and what chemicals are present in a contaminated air event. The UK House of Lords was advised by Lord Davies of Oldham in 2005 that, ‘There is no requirement for air quality monitoring exercises to be carried out during contaminated air events in aircraft, and there is no record of any such measurements in the public domain. Air quality measurements are normally only made as part of the initial certification of each aircraft type.’ [20] The point was even clearer in a statement by the UK Aircraft Health Working Group which stated in 2005 that, ‘air sampling has never been done during a fume event.’ [21]

Over the years, many crews have complained about contaminated air exposures to the airline industry but to no avail. The knock on consequence of this is the fact that most crews would not think about telling passengers that their exposure to contaminated air might be harmful or pose a flight safety risk as most do not realise this themselves. However, passengers and crews are experiencing adverse effects and are being harmed. While there has been information supporting adverse effects from exposure to synthetic jet engine oils dating back to at least 1977 and by committees set up by airlines specifically dealing with the contaminated air issue in the early 1990s, it is only since 1997 that there has been a heightened awareness of the problem. [22][23] It was a serious BAe 146 incident in Australia in mid 1997 that began a period of increased recognition of the problem. [24] There is evidence supporting that crews were voicing their concerns in the 1980s and early 1990s such as Dan Air, East West and Ansett Australia crews. [8][10][25]

Faced with a lack of knowledge, virtually no education of contaminated air effects and an industry saying that their were no harmful or long term health effects of exposure to contaminated air, there was always going to be a health and flight safety issue and there still is. Over the years, some crews have listened and learnt, some are ignorant of the risks or in denial, some blindly continue to trust the industry wrongly telling them it is safe, some do nothing to protect their pay and others have retired on medical grounds from the consequences of the exposures. While many groups within the aviation industry have indicated for years that leaking oil poses no threat, there is even within some of the major pilot unions significant denial or a lack of urgency to act for fear of the impact acting might have on the industry as a whole.

Two initial examples of the consequences of this ongoing flight safety problem are as follows:

  • The pilot in command of a BAe 146 reported that the smell of oil coming through the air supply was far worse than usual with the passengers and flight attendants complaining bitterly of the smell. The First Officer also complained of the smell, experienced worsening red / weeping eyes. On final approach to land the Captain slowly became aware of feeling, ‘as drunk as a skunk’ as if having consumed about 6 scotches. The captain reported having trouble judging the distance to land with everything seeming, ‘wonky’ including the runway. The Captain reported that the symptoms similar to intoxication removed all consideration of handing over control to the First Officer. The pilot grounded the aircraft and stated that further flight would not even be considered until fresh air was obtained to, ‘sober up’. [26]

  • On a Boeing 757 the crew smelt 'fumes' (oil fumes) on start up. Before take off the co-pilot felt 'strange / vague' but then recovered and take off was normal. A few minutes into the flight both flight crew suffered a slight headache and mild nausea. All symptoms cleared by about 20 minutes after take off. Oxygen was not used as it was not considered necessary; however after the flight both pilots reported headaches and nausea persisting. The next day, the Captain felt OK but the co-pilot who had experienced another exposure event 2 days prior felt very fatigued, dizzy, nauseous, vague, with a loss of balance. The Co-pilot rang the airline medical department which stated they had lots of calls on contaminated air and that a lot of this was, 'somosomatic' and would not allow the pilot to speak to a doctor. On investigation, one of the engines forward bearing feed and scavenge tubes were found leaking and the seals were replaced. The leaking oil had contaminated the Auxiliary Power Unit (APU). [27]

  • The US FAA sadly offers one of the most worrying examples of complacency. In 1990, the AFA petitioned the FAA to adopt the statutory protections of the OSH Act for airline crew members. Seven years after the AFA filed their petition, it was denied on the basis that:

    ‘The FAA has determined that the issues addressed in your letter may have merit but do not address an immediate safety concern.’ [28]

    Flight Safety Aspects of Contaminated Air:


    1. AIHA: American Industrial Hygiene Association. Odour Thresholds for Chemicals with Established Occupational Health Standards. 1995. ISBN 0-932627-34-X.

    2. British Aerospace (2001) Service Bulletin SB 21–150: Air conditioning - To inspect engine oil seals, APU and ECS jet pump and air conditioning pack for signs of oil contamination. British Aerospace Systems, Hatfield.

    3. Canadian Transport Bureau Interim report on Swissair 111 Accident. December 2000.

    4. AOPIS (2003) Aircraft Air Contamination: An Ongoing Health And Safety Issue, Documentary. Aviation Organophosphate Information Site. Available At:

    5. Australian Transport Safety Bureau Report (ATSB): Occurrence Brief 200205865. 2 December, 2002. Aircraft Registration: VH-NJX – BAe 146.

    6. ATSB Report: Occurrence Brief 200205307. 11 January, 2002. Aircraft Registration: VH-NJD - BAe 146.

    7. ATSB (2000) Occurrence Brief 200002431, BAe 146, VH NJL, Australian Transport Safety Bureau, Canberra, 2000.

    8. Dan Air. Memo. Capt L. Buist. BAe 146/300 SRS Aircraft. Passenger cabin smells / odours. 11 June 1991.

    9. Rayman R.B., McNaughton G.B. Smoke/fumes in the cockpit. Aviation, Space and Environmental Medicine 1983; 67: 738-740.

    10. BAe (1991) Complaint of difficulty report 27803. British Aerospace Systems, Hatfield.

    11. National Jet System BAe 146 oil fumes in summary, 17 November 1998.

    12. National Jet Systems (2000) Hansard Evidence by National Jet Systems to the Australian Senate inquiry into air safety (1999–2000) BAe 146 cabin air quality. Parliament of Australia, Canberra.

    13. CASA , CCH Australia OH&S magazine, Feb-Mar, 2003, High on the flight deck, Helen Borger.

    14. Civil Aviation Safety Authority (1999-2000) Hansard Evidence by CASA to the Australian Senate inquiry into air safety (1999–2000) BAe 146 cabin air quality. Parliament of Australia, Canberra.

    15. Australian Parliament Hansard, Q 398, BAe 146 aircraft, 2 December, 2002.

    16. Australian Parliament Hansard, Q3011: Air Safety - Cabin air quality, 29 March, 2004.

    17. British Aerospace (2000) Hansard Evidence by British Aerospace to the Australian Senate inquiry into air safety (1999–2000) BAe 146 cabin air quality. Parliament of Australia, Canberra.

    18. FAA: A.Azevedo (2005). Presentation made at BALPA Contaminated Air protection Conference. Data review of instances of in-cabin fumes from propulsion system events.

    19. House of Lords, Select Committee on Science & Technology Report. Air Travel & Health, 1999-2000 – Memorandum by CAA SRG.

    20. UK House of Lords written question. HL 2312, 1 December 2005: Countess of Mar.

    21. AOPIS letter to UK Secretary of State for Transport, D. Alexander MP. 12 May 2006.

    22. Montgomery MR, Wier GT, Zieve FJ, Anders MW (1977) Human intoxication following inhalation exposure to synthetic jet lubricating oil. Clinical Toxicology 11:423–426.

    23. A. Chew V East west Airlines and Ansett Australia. Compensation court of New South Wales. Matter 19652/95. Evidence given by Ansett Australia engineer. Mr. R. Cain 14, December 1998.

    24. ATSB (1999) Occurrence brief 199702276, BAe 146, VH NJF, Fumes in cabin.

    25. Flight Attendant Association of Australia (FAAA) (1999) Submission by FAAA to the Australian Senate Inquiry into air safety (1999–2000) BAe 146 cabin air quality. Parliament of Australia, Canberra.

    26. ATSB Report: Ansett BAe 146. Confidential submission , 1998 & Senate of Australia (2000) Air Safety and Cabin Air Quality in the BAe 146 Aircraft. Senate Rural and Regional Affairs and Transport References Committee, Final report. Parliament of Australia, Canberra. Confidential submission C10 (section 5.31).

    27. UK contaminated air database. B757. 22 September, 2005.

    28. AFA Submission to U.S. Department of Transportation Dockets: Docket No. FAA-1999-6342 - Response to FAA request for comments on occupational safety and health issues for airline employees. March 8, 2000.

    The Airline Pilots