There have been regular crew reports of airborne incidents in which cockpit and cabin air has been contaminated with engine oil fumes. This is particularly true in Germany, which has a respected system of compulsory safety reporting, but it is a universal issue with reports being filed by pilots in UK and US airlines, among others.

Because jet engine oil contains organophosphates that can be harmful to human health, the German government is pressing the European Commission to set common standards for dealing with the risk heated oil fumes pose by entering the cabin when engine oil seals leak. The fumes are introduced to the cockpit and cabin because air is continually drawn from the engine compressors for air-conditioning and pressurisation.

A higher level of sustained interest in cabin "fume events" by German news media compared with press elsewhere in Europe has contributed to a higher incidence of crew awareness there, hence increased levels of reporting. Nevertheless, Germany's aviation authority has voiced concerns that incidents of this type are still under-reported. Consistent German media interest is also likely to be a factor in the relatively high level of political involvement in the subject, up to German transport minister Peter Ramsauer, who has called for combined European action to eliminate or reduce the risk.


No section of the industry or the authorities deny "fume events" occur, nor do they deny they involve organophosphate neurotoxins. Although the issue's existence is recognised, it has such serious implications for the air transport and aerospace industries that when the subject arises, there is a great deal of uncomfortable shuffling of feet by government ministers and civil service bureaucrats, not to mention the airframe and engine manufacturers.

Government or agency statements issued on the subject of oil fumes in aircraft cabins generally avoid addressing it directly, using a package of dissembling techniques, the main one of which is to allege insufficient knowledge of the problem and to claim that more time is needed to study it. Although the chemicals involved are known neurotoxins and carcinogens, the UK Department for Transport (DfT) - to take just one regulator into account - sidesteps this charge by claiming, without pretending to provide any evidence, that all fume events are "occasional" and "brief" and, crucially, by claiming the concentrations are so low as to be harmless.

In the same breath, however, the DfT admits there is no established level for what concentration of these chemicals - or how much exposure to them - is medically acceptable, or beyond which they become harmful. This lack of existing standards allows the DfT to invoke the argument that there is a need for more study before conclusions can be drawn.

Meanwhile, when fume events are reported, the authorities keep the issue at bay by using the legal principle known as "burden of proof", which requires the party who alleges that there is a case to answer to prove it in law, while the party who denies there is a case to answer does not have to prove anything. So if there is a fume event following which crew and/or passengers report damage to their health, the burden of proof as to the cause of the medical symptoms lies with the victims.

The DfT explains its argument on its website: "Some pilots who have experienced these events report a variety of short or long-term symptoms or ill health. But it is not certain that these symptoms are work-related."

The DfT can allege that pilot neurological problems following a fume event might have been caused by some other circumstance in the pilot's life, not the fume event itself and, unless the pilot can disprove the DfT's proposition, the department's argument stands by default. For the crew and passengers, proving this negative fact - that their symptoms were not caused by something else - is notoriously difficult.

It is not only the authorities who dissemble. Here is an extract from Airbus's in-house technical journal, talking about a specific airborne incident involving a Germanwings A319 fume event in December 2010, quoting its own expert Dr Andreas Bezold: "It was very serious. For obviously the pilots were, on their own statements, almost unable to act, as this interim report by the Federal Accident Investigation [BFU] shows.

"This so-called 'incapacitation' is of greatest concern in terms of flight safety. That some passengers, flight attendants and pilots are now feeling potentially insecure is understandable. The fact is, currently, no-one knows the exact causes that led to this situation." In the Germanwings incident, both pilots suffered incapacitation and had trouble landing the aircraft safely.

A group of medical scientists led by Professor Clement Furlong at the University of Washington, Seattle, is not inclined to dissemble. This is an extract from a recent research paper they published describing the search for the biomarkers that will prove the connection between aircraft fume events and human health: "On most jet turbine aircraft, unfiltered engine bleed air is fed into the cabin, providing oxygen for those aboard. Exposure of passengers and crew to some level of triaryl phosphates [TAPs] occurs in approximately 23% of monitored flights, whereas higher levels of exposure can occur when engine oil seals wear or fail.

"Symptoms of aerotoxic syndrome resulting from such exposures can include extreme mental impairment, an acute flight safety issue when crew exposure to contaminated air is significant. Material safety data sheets for synthetic jet lubricants list TAP contents of 1-10%."

Just one example of these fume events concerned a Germania Boeing 737-700 flight from Milan Malpensa to Dusseldorf on 18 November 2011. German accident investigator BFU investigated it and reported that the co-pilot became physically sick and had to leave the flightdeck, then had to go on oxygen when he returned. After the flight, the co-pilot's blood tested positive for tri-ortho-cresyl phosphate, a known neurotoxin and a constituent of aeroengine oil. It is universally harmful to health, but individual reactions to single events can vary markedly, as in this case.

The same year, Air Berlin's Airbus A330 fleet suffered three harmful fume incidents which made the crew sick and, following one of the incidents, the airline made an unusually complete statement containing its version of what happened: "An odour was briefly generated both in the cockpit and the cabin of the Airbus A330-200 during the ascent and descent. The odour was also perceived by the cockpit and cabin crews before it rapidly dispersed. A report was submitted to the BFU.

"In this particular case, however," added Air Berlin, "there was no 'serious incident' within the meaning of EU regulation 996/10, so Air Berlin, by sending this supplementary report to the BFU, is primarily signalling that the final assessment of the incident should rest with a government authority."

The latter sentence is an appeal for the authorities to provide clarity on this issue, because the airframe and engine suppliers are not denying fume events happen, they just deny they have any harmful results to passenger and crew health, so it is the airlines which are left facing the consequences.

The consequences include many pilots and cabin crew who are no longer fit to fly, and although, of course, they could not prove their illness was not caused by some aspect of their off-duty life, airlines have made settlements with pilots and cabin crew whose flying careers have ended because of "aerotoxic syndrome" - not a piece of terminology the airlines accept, but which Professor Furlong's team has validated.

Speaking for the German pilots' union Vereinigung Cockpit, Jörg Handwerg says the problem is much more common than anyone admits, estimating that on average there are about 10 fume events each week across the entire German airline fleet. Getting down to where the problem originates - jet engines and their oil - the UK Air Accident Investigation Branch (AAIB) had this to say about a fume event in 2006 on a Boeing 757 with Rolls-Royce RB211-535E4-37 engines: "The engine lubrication system supplies pressurised oil to the main shaft bearings. Various methods are used to ensure that the air pressure external to the bearing chambers exceeds the local oil pressure, to prevent the oil escaping and contaminating the compressor air flow.

"If this should occur, oil mist can enter the bleed air system causing odour, fumes or smoke to enter the cabin by the air-conditioning system." That is what happened in this case, according to the AAIB bulletin describing the event, and the crew elected to carry out a diversion and emergency evacuation.


French aeroengine oil company Nyco has been working for some time to develop an oil with the same anti-wear properties as the one currently available, but containing chemicals that are less toxic when they do enter the air-conditioning system. Nyco chief executive Eric Piveteau says an oil under development at his company will be less volatile than existing products, reducing the risk of harm to passenger and crew health when fume events occur. He also hopes for improved "elastomer compatibility" in the oil, which would make engine oil seals last longer than they do at present, lowering oil consumption and cutting the risk of fume events.


The UK DfT claims on its website it has been actively monitoring the consequences of fume events: "To fill the knowledge gap, the DfT put four research studies in hand. All have been completed and the department's programme in this area has now stopped." The argument would appear to be that the DfT's studies have assembled the knowledge necessary to allow it to dismiss its concerns. Actually, this is not so, according to the same DfT website: "Both the Committee on Toxicity (CoT) and the House of Lords Committee on Science & Technology identified a gap in the world's knowledge. The independent [CoT] completed a substantial review of evidence in September 2007 and concluded that the evidence available did not establish a link between cabin air and pilot ill health, but nor did it rule one out."

So there is still a knowledge gap, the DfT admits but, despite this, it has stated its intention not to examine the subject further. In fact, the only DfT attempt to investigate the issue directly came when it commissioned Cranfield University to carry out a total of 100 flights with two different jets carrying equipment to capture any fumes. Cranfield reported that during the trial there were no fume events, yet the DfT has included the results of the trial in its claimed "four research studies" as if it had actually proven something.

Meanwhile, the UK Health Protection Agency's comment on the situation also invokes the argument that there is insufficient information: "The currently available information suggests that aircrew and passengers are not at additional risk due to chemical exposures in aircraft cabin air, at least for the compounds for which data are available. The CoT will reconsider this issue when a full set of measurement data are available and the Health Protection Agency will also provide advice as appropriate." However, the DfT says it is not going to do any more work on the issue. To quote an old English proverb: "Where ignorance is bliss, it is folly to be wise."

Dr Susan Michaelis, a former airline pilot who lost her aircrew medical category following fume events flying BAe 146-series aircraft in Australia, has carried out a study to PhD level at the University of New South Wales, dedicating more than 10 years to the assembly of established scientific data on the subject of cabin air contamination and its relationship to health - with her data going back to the 1950s. She said the CoT has consistently refused to accept her research for consideration, and it did the same for case studies submitted by the Global Cabin Air Quality Executive, a body set up in 2006. The CoT also did not accept data from the Aerotoxic Association, which assembles data on individual human health issues following exposure.

Meanwhile, there is no admission by the UK government of its obligation to ensure a safe working environment for the aircrew, or a safe cabin environment for the passengers, which it is required to do at ground-based workplaces and in other forms of public transport. The UK civil aviation authority distances itself from the politics of the situation by arguing that health and safety is not its remit, only flight safety is, and its argument is that flight safety in a fume incident is assured provided that the pilots get their oxygen masks on quickly enough.

The German government takes a different attitude and Ramsauer has written to the European Commission demanding action at EU level. Germany wants action but it does not want to act alone, because if German airlines were required to tackle the problem and their European competitors were not, the costs of German carriers would go up compared with those of its competitors.


The US authorities are clearly concerned, hence it issued this 17 July 2012 Request for Information: "The Federal Aviation Administration [FAA] seeks information from industry developers, manufacturers, and the public related to effective air cleaning technology and sensor technology for the engine and auxiliary power unit bleed air supplied to the passenger cabin and flightdeck of a pressurised aircraft.

The information obtained will inform the agency of potential research and development plans. Specifically, the FAA seeks information about bleed air cleaning, and contaminant detection and cleaning technologies, which are capable of removing oil-based contaminants from the bleed air supplied to the passenger cabin and flightdeck, and detecting and recording oil-based contaminants in the total air supplied to the cabin and flightdeck from bleed air."

Michaelis draws attention to the FAA's departure from its own precepts in this area, which the FAA is clearly aware of and is looking for a fix. The FAA's rules require a warning to pilots of any unsafe condition, but there is no requirement for a device to detect and warn the crew of the presence of pyrolysed oil fumes in the cockpit or cabin of any aircraft. In 2002, an FAA report acknowledged this: "No present airplane design fulfils the intent of FAR 25.831 because no airplane design incorporates an air contaminant monitoring system to ensure that the air provided to the occupants is free of hazardous contaminants."

So, like the Europeans and the rest of the world, the USA acknowledges the problem but appears to be in no hurry to do anything about it. Meanwhile, airline crew and passengers continue to be regularly exposed to pyrolysed oil fumes in flight, and some of them, according to the experience of documented cases being examined by Professor Furlong's team, will suffer harm. Only Boeing 787 passengers do not have to worry, because it does not use engine bleed air for its pressurisation and air-conditioning.

Source: Flight International