The Unique Challenges of Aircraft Cabin Air Quality and Fume Events
A 70 year old phenomena that has yet to be resolved!
We all like to think that the flight that we take is one of the safest and most efficient ways to move around the world.
Yet, for over 70 years there is a hidden issue which affects the health and comfort of passengers and crew: contaminated cabin air quality, often referred to as “fume events” or “aerotoxic syndrome”.
Despite industry assurances and regulatory frameworks, the argument exists that the standards governing cabin air quality are non-binding and not legally enforceable. Regulators in Europe would counter that by stating that an airline or manufacturer has to demonstrate compliance with regulation otherwise there can be no certification of product nor indeed operations.
But this evident gap not only leaves many questions about how passengers and crew are truly protected, but it also cuts to the heart of how these standards are created, perhaps suggesting a ‘Patriarchal’ or ‘Doctor know best’ methodology in their creation.
A good example of that is found through the work that I and colleagues from across Europe took part in, to challenge an existing European Standard on Cabin Air Quality, created by Aviation professionals, with no aircrew, their representatives nor consumers in the room during its creation. The Standard in question was overturned and new work was created to develop a new Standard for Cabin Air Quality. But for Standards that form part of the regulatory environment, there is no such diverse engagement apart from the apparent ability to comment via the Regulator’s commenting tool. It is an important and revealing gap which I shall talk about more in the future.
This article explores why the unique environment inside an aircraft cabin demands a different approach to air quality standards than those used for ground-based indoor environments. It also highlights the challenges in regulation and offers insight into why this system of ‘regulation’ falls short of addressing the real risks.
What Are Fume Events and Why Do They Matter?
The air that you breathe on your flight is extracted from the air within the aircraft engine. Fume events occur when contaminated air enters the aircraft cabin, often due to leaks in the bleed air system that draws air from the engines. Those leaks usually occur during the transient stages of the flight, where the aircraft engine experiences different power ranges, along with the effects of changing pressure as the flight ascends or descends. As a result of those transient changes, the seals within the engine can suffer a less than optimal operation and synthetic oils used within the engine can leak into the air that is extracted through the bleed-air system. Another engine on the aircraft can also present similar leakages, this being the Auxiliary Power Unit or the APU, which is the small engine found in the tail of civil aircraft, which generally helps to power the aircraft whilst it is on the ground. Extracted air can carry synthetic oil, hydraulic fluids, or other re-combined chemicals, which may cause symptoms ranging from mild irritation to serious health problems for those exposed.
Passengers and aircrew have reported:
Headaches;
Dizziness,
Respiratory issues;
Skin Rashes;
Sight problems, and
Neuro-degenerative and Cognitive difficulties after experiencing fume events;
This list of adverse health effects is not intended to be exhaustive.
The difficulties that arise from the extraction of bleed-air can not only affect passengers and cabin crew, but importantly, pilots; this issue cuts into the very heart of the safe operation of your flight.
A common question asked is how many events arise. That is a difficult question to answer because of the difficulty in establishing verifiable data. With that caveat, I cautiously present a recent survey I carried out, where I examined flight reports over 4 years. I concluded that some 1.29 flights were globally affected each week by fume events. Now that may not seem like a lot of flights, but I also estimated that my sample survey very likely only represents some 5% of verifiable fume event reports (there is a distinct possibility that this percentage figure may be lower, but I prefer to take a conservative approach where data is not widely available). If therefore my assumptions are correct, then this would suggest that some 25.8 flights are globally affected by fume events each week. By any measure, this strongly suggests that this is a flight safety issue of concern.
Why Current Aviation Standards Fall Short
The aviation industry and regulators will often rely on the mantra that the air onboard your flight is better than that found within your home or office. Industry will often speak to how the aircraft environment is created to mimic or represent the environment that you are used to experiencing in your home or at work. The problem however is that the solutions provided for the aircraft environment, is based on standards developed for indoor air quality in homes and offices to assess cabin air safety. These ground-based standards set thresholds for pollutants and contaminants based on environments at sea level and normal atmospheric pressure.
By implication, the narrative avoids the very obvious point, that being that the aircraft environment is a unique environment and is quite distinct to that which you experience at ground level.
For example, the aircraft environment operates under very different conditions:
It is a closed and sealed environment (there are some within the industry that claim that it is a semi-closed environment because it extracts breathable air from the aircraft engine);
The aircraft operates at high altitude;
That closed and sealed environment is subjected to altitude and pressure changes: Cabin pressure at cruise height is maintained at levels of between 6,000 to a maximum of 8,000 feet above sea level. But remember, that pressurisation begins at ground level and through the changes during the ascent and descent of the aircraft, these temperature & pressure changes can affect how chemicals behave and how the human body reacts;
The aircraft environment, because it is a closed and sealed environment, undergoes an air recirculation process, exchanging 50% of breathable air every 3-5 minutes with the new air being introduced from the bleed-air system. The old air is jettisoned from the aircraft;
Pressurisation is necessary to prevent the aircraft occupants from suffering with Hypoxia, Altitude Sickness, Decompression Sickness and Barotrauma – a factor that most of us do not have to contend with during our day-to-day lives on the ground.
It therefore is clear, the aircraft environment is unique and considering ground-based environments against it is in my opinion, incorrect.
Because of these factors, applying ground-based indoor air quality standards to aircraft cabins, ignores the unique risks and conditions within an aircraft and the recognition that despite the presence of HEPA filters on many aircraft, fume events and the various chemical compounds are still experienced during flights.
Implications for Regulation and Safety
Regulators, manufacturers, airline and engineers, must codesign regulations and a standard that are distinct and reflect these conditions rather than adapting ground-based models. This means:
Accepting the unique nature of the aircraft;
Working in partnership with Aviation Users;
Presenting openness on the question of the constituents of synthetic oils, hydraulic fluids and other fluids or chemicals used on aircraft;
Understanding the nature of these constituents and how they operate within a high temperature, variable pressured environments;
Understanding the potential effect of such constituents on human health;
Design testing models that are appropriate and produce better outcomes to assess the said effects on human health;
Establish the correct comparator(s) for the aircraft environment, for example, other vehicles that operate within high pressurised environments (space vehicles, submarines etc);
Embracing the Precautionary Principle;
Reconsider the use of probability, a traffic light warning system, language surrounding the potential on failures and to create a new language that is not reliant on subjectivity but on data;
In Europe, work to create a better and more appropriate Common European Risk Classification Scheme based on data and cooperation;
Work in partnership and codesign on the question of Artificial Intelligence and the use of AI Systems which have the potential to be deployed within cabin air quality issues;
Setting exposure limits based on the previous factors and the cabin pressure and altitude.
Codesigning real-time air quality monitoring onboard;
By codesign to adopt or create a comprehensive hierarchy of controls;
By codesign creating filtration and ventilation systems specifically for aircraft environments;
Mandating transparent reporting and investigation of fume events;
Creating solidity in that reporting by protecting aircrew under current EU whistleblowing provisions;
Outlawing penalties or other sanctions from being applied against aircrew where they become ill as a result of fume event;
Both of the aforementioned issues relating to aircrew support the ‘Just Culture’ provision found within EU Regulation;
To adopt or create a medical protocol for aircrew and passengers, for use by aviation medical professionals and state-based medical personnel;
Accepting the principle of a passengers right to know and to receive assistance;
By codesign to create and develop a distinct European Aviation Safety Programme/European Aviation Safety Plan specifically for Cabin Air Quality;
By codesign to recognise the disparate nature of current EU Aviation ‘Regulation’ on Cabin Air Quality and to create unifying or harmonised ‘regulation’ that recognises all the factors contained within the points above.
Moving Forward: What Needs to Change?
A couple of days ago, I attended the inaugural meeting of a newly formed APPG (All-Party Parliamentary Group) on Cabin Air Quality. It was almost 20 years since I first attended the UKs Parliament, meeting as I did with some very brave pilots and cabin crew. It introduced me to a new world, working as I did, and still do, with some remarkable activists.
As I listened to the presentations made by my colleagues, I marvelled at how far we had come, both in understanding and knowledge.
But it was the testimony of aircrew that was shocking. It would not be correct for me to share the detail of what they shared with me privately after the event concluded. The people I spoke with are highly professional; sad that their exposures to toxic fumes has prevented them from continuing to work in the industry that they love. The stories they shared with me about their treatment, was, despite the fact that I have heard similar tales, still shocking; the airlines of Europe should hang their heads in shame for what is done to what are clearly decent and honourable people. Their only crime, if it is indeed a commercial crime, was to raise concerns and unfortunately, suffer the health deficits arising from the problem stemming from the air supply into their working environment.
I have a demonstrable record on working with all sides of this debate and helping to achieve a consensus. But, apart from other issues I have highlighted in this article, the one thing that needs to change is the culture found within airlines, manufacturers and indeed, insofar as Europe is concerned, within parts of the Regulator and the European Commission. It is all very well to speak about ‘Just Culture’ or a ‘Safety Culture’, but, if one of the distinct problems we all face attaches to a ‘Collective Culture’ or a ‘Commercial Culture’, then progress will never be satisfied. My door has always been open; the same cannot always be said for some of the industrial or political actors in this debate.
However critical I am about an industrial or political culture; I am also critical of Consumers. For some 30 years I have been at the heart of Consumer Rights and arguing for improvements in policy and legislation. But I have a sense that there is only one thing that is important for Consumers when they take a flight and that is the cost of that flight; anything else appears to be almost irrelevant.
I have spoken with many consumers who have experienced aircraft fume events; some have been rendered unemployable. Those consumers have become vocal following their experiences but face difficulties with commercial entities, medical professionals and in some cases, legal representation. I have observed in recent years, the consumer of today is not the consumer of the 1990s. Consumers of today appear to not want to be inconvenienced, to pay the lowest possible price for their product and to want any solution to their problems to be swift (often through poor advices on social media), if indeed they seek a solution at all. If this is the ‘Consumer Culture’ of 2026, then it too needs to change, because the issue of cabin air quality is a real issue and could affect their next flight. The question is simply this: ‘Would you as a consumer accept a product that that presents a deficit?’ We can accept I hope that consumers would not; they would enquire and challenge and seek a solution. So if that is the case, do consumers not realise that they have immense power when it comes to aviation?
Imagine if consumers started to contact the airlines they intend to travel with and asked two simple questions (they could even ask the same questions of the regulator):
‘How many fume events have you experienced on your flights and how many have you reported to the regulator this year?’
‘How do you deal with fume events when they occur on your flights?’
Two simple questions that could lead you to making different financial choices; two questions that would make Regulators and the Industry sit up and listen.
That is how change begins!
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