The debate surrounding the subject of Cabin Air Quality (CAQ) and "Aerotoxic Syndrome" is both fierce and contentious. Broadly speaking, opinion on the matter can be divided into two camps.

On one side of the argument are the large self interest groups - aircraft manufacturers, engine manufacturers and the aircraft operators.

On the other side of the argument are those likely to be affected by Cabin Air Quality events – pilots, crew, and passengers, supported by a growing number of independent experts and documented evidence.

It is evident that the different perspectives on the argument give rise to passionate and heated discussion. Each side is firmly of the belief that their opinion is correct.

The issue is not new. In 1954, the United States Air Force identified the potential for damage to health from heated components of synthetic jet engine oil. The tests conducted on animals produced pneumonitis and degenerative changes in the brain, liver, and kidneys. The higher the temperature at which the oil vapour is formed, the more toxic it becomes.

As far as it affects those on board the aircraft, the issue is fairly straightforward. As long as the synthetic compounds that cause the problem are contained within the areas where they are designed to be – the engines and APU – there is no problem.

The hazard arises when the harmful pyrolised elements migrate. The vapour and aerosols escape into the aircraft cabin through the air conditioning system, either as a result of design flaws, maintenance errors, or the breakdown of the various labyrinth and other seals within the aircraft power plants.

In order to clarify the issue succinctly, there are three questions which need to be asked.

  • Firstly, is there the potential for contaminants to enter the aircraft cabin?
    • Yes. There is sufficient evidence within the industry to confirm that proposition.
  • Secondly, are the fumes encountered in CAQ events hazardous to health?
    • Yes. Historically, medical studies have identified adverse short and long term effects to health.
    • Pilot reports have described symptoms ranging from mild discomfort and nausea, stinging eyes and impaired vision to complete incapacitation.
  • Finally, is there a flight safety implication associated with CAQ events?
    • Yes. Pilots have reported difficulties in concentrating and completing even the most basic tasks.
    • In the most extreme cases, there is evidence of pilots becoming completely incapacitated resulting in the diversion of the aircraft.


CAQ and fume events should not be taken lightly. Should you be unfortunate enough to experience such an episode, your first course of action should be to follow the appropriate smoke and fumes drill in the aircraft QRH, This drill will invariably require the pilots to don oxygen masks at some stage during the procedure; consider oxygen for passengers and a diversion. Sound advice. Always report the event via the appropriate channels. A technical log defect report along with an ASR is required for suspected oil fume events as is an MOR under the EU directive and corresponding National legislation. [1,2,3,4] Always seek medical help or advice following a CAQ event.

Importantly, after 3 minutes of exposure to an odour, the subject’s perceived intensity of the odour is reduced by about 75%. [5] Therefore it is vital that oxygen is used without delay.

There is a guide, which your medical practioner can follow, to assist in an accurate clinical diagnosis.

It is available here:


More background reading on the subject is available via the following links:


The PPU believes that Cabin Air Quality and Aerotoxic events are a serious concern.


They pose an immediate threat to flight safety and are potentially hazardous to health in the both the short and long term.


They should not be taken lightly.


We believe it is essential that pilots report any and all events via the normal channels and also copy in the PPU in order that we can acquire data on the subject and track the number and magnitude of the events.


[1] ECC (2008) European Communities Council Regulation 3922/91 as last amended- Commission Regulation (EC) No 859/2008OPS 20 August 2008. 1.420 b) 4- Occurrence Reporting.

[2] European Parliament and Council (2003) Directive 2003/42 of the European Parliament and of the Council. Occurrence Reporting in Civil Aviation. 13 June 2003.

[3] Civil Aviation Authority (2005) CAP 393 Air Navigation The Order And The Regulations Amendment 1/2005: Article 142 (3&4) .– 21 October 2005

[4] CAA (2005) Civil Aviation Authority, UK. CAP 382. The Mandatory Occurrence Reporting Scheme. July 2005.

[5] AIHA (1995) American Industrial Hygiene Association. Odour Thresholds for Chemicals with Established Occupational Health Standards. ISBN 0-932627-34-X. 1995