A subject that needs airing. Again.

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.

This is a schematic diagram, used to train engineers, of a gas turbine engine labyrinth oil seal.

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.










Shoreham and the future of air shows

No person or organisation associated with the 2015 Shoreham flying display accident escaped criticism – implied or actual – in the Air Accident Investigation Branch’s final report.

When the aircraft that later crashed, the Hawker Hunter T7, took off from its North Weald, Essex base heading for Shoreham to fly the display, it had several time-expired or unserviceable components in it. In retrospect the AAIB report says it was not in compliance with its permit to fly, yet none of these faulty components caused the accident.

The Flying Display Director hired to manage show safety was fully qualified in terms of knowledge, experience and expertise to oversee all aspects of the flying display, but the report implies there were some things – like the exact display routine the Hunter was to fly – he should have risk-assessed manoeuvre by manoeuvre. Yet even if he had, the crash might still have happened.

The Hunter’s pilot was fully qualified in terms of experience, training, flying recency and medical fitness to carry out the display he had planned, but on the day he got one of the aerobatic manoeuvres badly wrong, making mistakes that are difficult to understand in somebody so experienced.

The mistakes meant that he himself was seriously injured when thrown clear of the aircraft on impact with the A27 highway next to the airfield, but 11 people on the road were killed.

By flying a similar Hunter through the same manoeuvres, the AAIB has determined that the pilot could not have pulled the aircraft out of his “bent loop” without hitting the ground once he had passed the apex too low and failed, at that point, to carry out an “escape manoeuvre” by rolling the aircraft upright.

If he had used his ejection seat during the high speed descent from the loop it would not have saved him, and the pilotless aircraft would have continued to impact with the ground, possibly in much the same place. The only way the pilot could have prevented killing the people on the A27, says the report, was to crash the aircraft into nearby fields, but during the last second or so he probably still hoped he could avoid harm to road-users by pulling up in time.

Why was he too low at the loop’s apex?

He should have entered the loop from a 500ft base, but he started at about 185ft. The height of the top of a loop compared with the entry height is a product of speed and engine power at entry. The aircraft should have entered at a minimum 350kt with full power selected, but the Hunter entered at 310kt with less than full power until well into the pull-up. The pilot should have aimed for a 4,000ft apex with 150kt indicated airspeed over the top, but in fact it got to less than 3,000ft with 105kt.

Unless the pilot recognised the lack of energy at that point and carried out the rolling escape manoeuvre, he and the aircraft were doomed.

Why a pilot with so much experience of teaching, let alone flying, aerobatic manoeuvres failed to heed these indicators that the loop was going wrong may never be known, because trauma has obliterated the details of the fatal flight from the pilot’s memory, according to the report.

Air shows involve risk. A study by the AAIB has recently quantified that risk, and my blog a year ago describes the findings in detail.

The final Shoreham report confirms the impressions given by the earlier AAIB bulletins on the subject. Because no-one in an on-site air display audience in UK has been killed since the early 1950s, such success appears to have led to complacency.

Not rampant complacency, but a relaxed belief that all the people involved are experts who know what they are doing, so they don’t need to be given the third degree before a show.

The sign that not all was well was the number of serious air display accidents, mostly fatal, that occurred just outside the area controlled by the display organisers – just like the Shoreham Hunter crash.

The AAIB found that 65% of all air show accidents came into that category, but almost always the only person harmed was the pilot. So nobody, including the CAA, raised the alarm, until now.

Meanwhile aerodromes used for decades as air show venues have suffered encroachment at their boundaries by expanding residential and industrial development. This affects the profiles aircraft are allowed to fly during a display, and flight display directors are bound to take this into account.

No longer are display lines, and entry and exit profiles dependent purely on where the display audience “crowd line” is, they have to take into account what each aircraft would have to do in the event of a technical or operational mishap during the display to avoid crashing into a nearby populated zone.

These are considerations that will affect air shows in the future. If a flying display stops being exciting, it might as well give up. Or go somewhere else more rural.

Coastal air displays will survive, because the escape route for aircraft in trouble is obvious.

The best example of the conundrum air show organisers face is what has happened to the traditional Red Arrows display at the biennial Farnborough International Air Show. When the Reds reviewed their Farnborough routine in detail following the tightened guidelines published in the early Shoreham bulletins, they found they had to curtail their display considerably.

In a statement following the release of the Shoreham final report, the CAA says: “We are fully committed to ensuring that all air shows take place safely, for the six million people who attend them each year in the UK and for the communities in which they take place.”

Let’s hope the CAA means what it says.

Fear of drones

It looks as if the 17 April “drone strike” on a British Airways aircraft on approach to Heathrow airport may not have been a collision with a drone after all. Maybe just a wind-tossed plastic bag – the investigation is still in progress.

In an aircraft travelling at about 150kt (170mph/275km/h) on final approach, small objects can suddenly appear and flash past. At that point the pilots are concentrating on monitoring the aircraft’s performance and aiming it at the runway. So it’s easy for a pilot to misidentify whatever the object is.

But does that mean we don’t need to worry about drones?

There some very simple rules about how you may operate a drone, so the relevant question is whether people will obey the rules – or even read them in the first place.

Drones are getting popular among ordinary people, mainly for airborne video recording or still photography. First the selfie, then the selfie-stick, now the airborne selfie?

Lads mags are full of enthusiastic advice for gadget-crazy young men. Some lads will be given a drone as a birthday present. If they are given one, will they read the operating instructions when they’ve opened the pack, let alone the legal restrictions on their use?

Some won’t, but does that mean they will inevitably operate their drone in such a way as to endanger aircraft? The law of averages says that one day someone will – possibly unintentionally – fly a drone in an airport approach or departure path.

But given another contemporary public threat to aircraft – commercially available hand-held laser pointers being shone into pilots’ eyes during take-off or final approach to land – an unsettling mentality exists out there. Use of lasers in this way is against the law, but incidents are on the increase.

So when a drone hits an aircraft, what will the result be?

Most are small and light – between one and 5kg. If one of these hits the aircraft wings, tail or forward fuselage it will cause damage but not make it impossible for the pilots to fly safely.

But if it hits the flightdeck windscreen or the engines the results could be serious. Exactly how serious we are not sure, because tests have not been carried out.

A drone-strike on an engine will probably cause its failure, and if it’s a heavier device it might smash the windscreen and injure or kill a pilot. Either of these events is very unlikely to be terminal for the aircraft, but they both could be. This would depend on the degree of direct damage and whether or not it has secondary effects.

Large-scale public drone use is still not with us, but it’s on the way. With greater use will come greater awareness among users as well as the public. That’s what the Civil Aviation Authority and Department for Transport are banking on – the public’s basic common sense.

Terrorists are unlikely to use drones against aircraft because there are more effective ways of attempting to disrupt commercial aviation.

But for those on the fringes of society – the kind who use powerful laser-pointers – dicing with risk can be attractive.

What the authorities have to decide is whether this risk is serious enough to require, for example, all drone users to register. Or some form of unique identifier like a transponder or GPS tracker to be fitted to all machines.

They’d rather not have to introduce expensive bureacracy to control the public use of devices that, used sensibly according to existing rules, are pretty much harmless.