An unpredicted jet engine design flaw means that all commercial airliners in service today – except one – technically fail to meet the regulatory standards for cabin air quality, according to a new study carried out at Cranfield University, UK.
The Boeing 787 is the exception because – uniquely at present – it doesn’t use engine bleed air for cabin pressurisation and air conditioning. In other types, air for the cabin is bled directly from the compressor of the aircraft’s engines, which makes them vulnerable to an overlooked secondary effect of jet engine lubrication system design.
The design flaw relates to so-called labyrinth and mechanical oil seals that act to contain the lubricant supply to the engine-shaft bearings. Effective lubrication depends on a low level of oil flow through them. In terms of engine oil consumption this leakage is negligible, and it was assumed by engineers that high air pressure would prevent oil leakage into the compressor chamber.
Arguably the seals do exactly what they were designed to do, but the assumption about the effect of high air pressure preventing leakage into the compressor turned out to have been over-optimistic. This matters, because aero engine lubricating oil – an entirely synthetic fluid, not a mineral oil – contains organophosphate additives (tricresyl phosphate) that are highly effective anti-wear agents, but are also particularly toxic to humans.
A 2014 study by Robert Flitney, a sealing technology consultant, established that oil from the bearings does indeed leak into the compressor chamber despite the high air pressure in it. As Flitney explains: “Simply put, the labyrinth seal is essentially a controlled leakage device relying on pressurisation to minimise oil leaking along the compressor shaft.” It may indeed minimise it, Flitney found, but it does not prevent it. As a result, the lubricant that escapes from the seals into the hot environment of the engine compressor chamber are continuously – and inevitably – delivered as pyrolised fumes via the engine bleed air system into the cockpit and cabin. Mechanical oil seals similarly leak a small amount. Meanwhile the bleed air flow to the cabin is not filtered, and there are no detection systems anywhere on the aircraft to measure contamination levels or to alert crews to contamination risk – nor is a detection system mandated.
The latest empirical examination of the cabin air issue was carried out at the UK’s premier aeronautical university, Cranfield. The same establishment in 2011 produced a report into cabin air quality commissioned by the UK Civil Aviation Authority on behalf of the Department for Transport (DfT). At the time, controversially, the study confirmed that engine oil fumes were indeed carried into the cabin, but the first Cranfield study proposed the contaminants were not a hazard to human health at the levels measured.
The report admitted, however, that during the period in which the study team was taking cabin air samples for analysis, there was no occurrence of a “fume event” – an incident in which higher concentrations of oil fumes enter the cabin. Sometimes this is because of the failure or partial failure of an engine oil seal, but it can result from a simple variation of engine power, which varies the internal gas pressure and temperature distribution and affects the seal effectiveness. As the DfT says: “The science is difficult because fume events are unpredictable and can last just a couple of minutes.” It also states that its research into cabin air quality “has been completed and the department’s programme in this area has now stopped”.
Fume events are not everyday occurrences, but neither are they very rare. Their exact frequency is undocumented, partly because the industry and government agencies play down their significance, and the reporting rate per occurrence is unknown. The issue that is particularly carefully ignored, however, is the continuous presence of low level cabin air contamination resulting from the fact that engine oil-seal leakage, it has now been established, is effectively a designed-in phenomenon.
This exposes those who fly for a living – and also frequent fliers – to the risk of the cumulative effects of neurotoxins that can build-up in their systems even if they don’t experience a fume event. The DfT itself admits that the chemical constituents of aero-engine oil are potentially neurotoxic, but maintains that the levels of exposure are so low as to be harmless. The DfT has not, however, carried out any research into the cumulative medical effects of low level exposure despite hundreds of pilots and cabin crew having had to retire because of ill-health, some following fume events, but rather more suffering long-term health degradation from continuous exposure. As the DfT admits, however, its studies into this phenomenon have now stopped.
But the latest study related to cabin air quality carried out at Cranfield is an independent one, and it examined the issues relating to engine design. It also highlighted the failure of regulatory organisations like the DfT or EASA to enforce laid-down standards for bleed air system certification. The study, for which Cranfield holds the copyright, concludes: “Low-level oil leakage in normal flight operations is a function of the design of the pressurised oil and bleed-air systems. The use of the bleed-air system to supply the regulatory required air quality standards is not being met or being enforced as required.”
This study was carried out at Cranfield by Dr Susan Michaelis, a former airline pilot who, in 2010, had been awarded a PhD by the University of New South Wales, Australia for her paper entitled “Health and flight safety implications from exposure to contaminated air in aircraft”. In 2016 Cranfield added an MSc to her academic achievements. The result of the MSc research is her new paper “Implementation of the requirements for the provision of clean air in crew and passenger compartments using the aircraft bleed air system “, which also won Dr Michaelis the accolade “best overall student on the [Cranfield] MSc Air Safety and Accident Investigation” course .
Meanwhile the European Aviation Safety Agency has produced an industry-led study that has more or less re-hashed all the old industry arguments, the main tenet again being that although potentially harmful organophosphate-based fumes are present in bleed air, the concentration is so low as to be harmless. EASA doesn’t address the issue of repeated crew exposure to low levels of harmful toxins and occasional “fume events”, and where it has been established that specific crews have suffered medically identified symptoms, including incapacitation in flight. EASA’s report has dismissed them as psychosomatic.
Now the University of Stirling has just had a paper published (June 2017) in the World Health Organisation’s journal Public Health Panorama. It examines “the health of aircrew who are suspected to have been exposed to contaminated air during their careers,” and says the study shows “a clear link between being exposed to air supplies contaminated by engine oil and other aircraft fluids, and a variety of health problems. Adverse effects in flight are shown to degrade flight safety, with the impact on health ranging from short to long-term”.
The report confirms that more than 300 aircrew, whose cases were examined, “had been exposed to a number of substances through aircraft’s contaminated air and reveal a clear pattern of acute and chronic symptoms, ranging from headaches and dizziness to breathing and vision problems”. One of the report’s authors, Professor Vyvyan Howard, professor of pathology and toxicology, Centre for Molecular Biosciences at the University of Ulster, added: “What we are seeing here is aircraft crew being repeatedly exposed to low levels of hazardous contaminants from the engine oils in bleed air, and to a lesser extent this also applies to frequent fliers. We know from a large body of toxicological scientific evidence that such an exposure pattern can cause harm and, in my opinion, explains why aircrew are more susceptible than average to associated illness.”
Recorded fume events causing sensory impairment and incapacitation of pilots and cabin crew are numerous, but listing them all is of limited use because the stories are remarkably similar. In terms of scale, an event over Canada on 24 October last year is notable because it involved an Airbus A380, but similar events have been recorded on all types large and small. In the A380 case British Airways flight 286 en route San Francisco-London was over Saskatchewan when it was forced to divert to Vancouver with a major fume event that incapacitated at least eight crew members, forcing them to go onto oxygen. When it landed all three pilots and 22 cabin crew were taken to hospital, and many of them were unfit for work months later, according to their union, Unite. The condition of the passengers is unknown. There has been no formal inquiry by British authorities into the event, and BA was left alone to deal with it. BA says the aircraft’s flight back to London was uneventful.
Some individual aircraft become notorious for fume events but remain in service with no follow-up by the authorities. An example is N251AY, a US Airways Boeing 767-200. On 16 January 2010 it operated a flight from St Thomas, US Virgin Islands, to Charlotte, North Carolina with 174 passengers and seven crew on board. During the flight the cabin crew noticed an unpleasant smell in the cabin, and the pilots suffered the onset of headaches, sore throat and eye irritation. By the time they were managing the approach to Charlotte they began to feel groggy and had difficulty in concentrating, but they landed the aircraft safely. During the en-route phase the pilots had messaged base to request medical attendance on arrival.
The event has been confirmed by US Airways but is not recorded by the FAA or the National Transportation Safety Board. Crew blood tests on arrival confirmed high levels of carboxyhaemoglobin, all the symptoms persisted for days, and the feeling of fatigue never left the pilots. They had their aircrew medical clearance rescinded and lost their pilot licences.
In March the same year the US Association of Flight Attendants reported that eight pilots and cabin crew members, including all but one of the crew on the St Thomas-Charlotte flight on 16 January 2010, did not return to work, and that there had been at least three known fume events on N251AY in December and January. The only fault the airline said it found was leaky rear door seals which, arguably, could have allowed engine fumes into the cabin on the ground, but the AFA says it doubts that explains what actually happened.
US Airways had carried out a borescope check on N251AY’s engines but initially found no engine fault. Dr Michaelis points out, however, that there did not have to be a fault for oil seal leakage into the compressor to take place. Her Cranfield work explains that oil seal leakage is lowest during stable flight phases like cruise, but in transition phases like start, spool-up, throttle-back, or whenever the power is varied, the pressure and thermal equilibrium is disturbed, and a fume event can occur even when there is no bearing fault. Hence the frequency of “no fault found” reports from the engineers after post-fume-event inspections.
Meanwhile internal reports and messages by official agencies about cabin air contamination also abound, but again they all say much the same thing. Here is one example of a US FAA report in 2009 recorded, along with many others, in one of Dr Michaelis’ research papers. The FAA said: “Lubricants: Many incidents of smoke/fumes in aircraft cabins have been linked to contamination of cabin air with pyrolytic products of jet engine oils, hydraulic fluids, and/or lubricants by leaking into ventilation air. These leaks can be subjected to 500°C or higher temperatures. If the origin of the smoke/fumes is of organic petroleum derivatives, then the smoke/fumes may cause a multitude of symptoms, including central nervous system dysfunction and mucous membrane irritation.”
Ever since the US Watergate political scandal and cover-up, when news media are following such a story they tend to tag it as a cover-up by suffixing the key word with “gate”. In what is perhaps the most notorious aviation industry alleged cover-up – the Westgate affair – the suffix was already in place. Richard Westgate was a British Airways A320 pilot when he died at age 43 in December 2012.
Westgate had been treated by a specialist clinic in Brussels for a painful neurological disorder for more than a year before his death, and extensive neurological damage was confirmed by his post-mortem. But when the coroner, Dr Simon Fox, QC, ruled on the cause of death, he stated it was the result of a self-administered, non-intentional overdose of pentobarbital, a sedative taken to aid sleep. Westgate died alone in a hotel room in Brussels.
Fox explained in his judgement that, although Westgate may have been exposed to organophosphate neurotoxins as a result of his job, and although that may have caused his poor health, it was not the cause of his death. He also ruled that there had been no causative negligence by British Airways, the Civil Aviation Authority or the Health and Safety Executive, basically because there are no prescriptive rules or guidelines relating to cabin air quality. Effectively, there are no applicable laws, so nobody broke the law.
Fox stated: “My provisional view subject to representations is that, whether or not in life in the period of months or years before his death the deceased was suffering from an illness caused by exposure to organophosphates in the course of his employment as a commercial pilot, is not a proper issue to be the subject of the Inquest.” In a statement that the dead pilot’s mother, Judy Westgate, read out after the judgement, she concluded with the words: “One day the truth will out.”
The subject of contaminated cabin air is to be reviewed by scientists, medical experts and engineers at the International Aircraft Cabin Air Conference at Imperial College, London on 19-20 September 2017 https://www.aircraftcabinair.com. Potential solutions to the problem will be aired as well as research and reports.
Meanwhile the industry and its regulators repeat the mantra that contaminants in the bleed air are at a harmless level of concentration. Dr Michaelis, in her studies, cites numerous, detailed, publicly recorded scientific data sources that all indicate there is no such thing as a safe level of exposure to the chemicals in aero-engine oil, especially when they are released in the form of pyrolised fumes.
But the industry can claim what it likes because it does not have to prove its case. In courts, the legal burden of proof rests entirely on those who claim to be victims of cabin air toxins, and it seems not to be sufficient to demonstrate – as in the Westgate case – that leakage of neurotoxic organophosphates into the cabin air is continuous and inevitable, but that the observable neurological harm to crew was not a coincidence nor psychosomatic.