Photo: Wall Street Journal
In December 2025 the Wall Street Journal published an article as part of a major investigation into pilot and cabin crew injury and deaths following exposure to toxic fumes onboard aircraft. The article documents multiple fatal outcomes after documented fume events and repeated low-level exposure, and highlights what affected families, pilots, and scientists have been saying for years: contaminated bleed air is a flight-safety issue and a serious public-health hazard. What follows are extracts from that investigation, followed by the scientific and engineering context the aviation industry continues to ignore.
‘He was poisoned.' Toxic fumes on planes blamed for deaths of pilots and crew
Story by Benjamin Katz - 21 December 2025
‘An American Airlines pilot, Ron Weiland was 54 years old and in good physical shape when he mysteriously lost his ability to play ping pong.
During a game with his wife and two neighbors in October 2016, Weiland swung and missed the ball entirely when trying to serve. He missed easy shots that he would normally smash away.
Weeks later, after a cocktail at a friend’s house in Lake Worth, Fla., he started slurring his words. “You did just have one drink in there, right?” his wife Martha asked him.
Weiland made his last flight in May 2017, after he had trouble making his passenger announcements. In June of that year he was diagnosed with amyotrophic lateral sclerosis, or ALS, a rapid neurodegenerative disease that kills the brain cells needed to control muscles in the body.
Weiland died on Jan. 14, 2019.
Two months before the ping pong match, Weiland had noticed an intense smell of engine oil as he was taxiing his Boeing 767 down the runway at Miami International Airport. He aborted the flight, offloaded the passengers and stayed on board to help the mechanics.
As the engines ran, the smell came back, along with plumes of a fog deep enough that he struggled to see beyond the first 15 rows.
The incident was what is known in the industry as a fume event, when leaks of synthetic oils or other fluids into an aircraft’s engines produce toxic gases that are released into the cabin and cockpit via the air supply.
The effects of fume events are often fleeting, mild or present no symptoms at all. But some passengers and crew members have been diagnosed with long-lasting and severe illnesses.
In the most extreme cases, including Weiland’s, fume events have allegedly been fatal.’
‘On July 17, 2015, James Anderberg had been piloting a Spirit Airlines flight from Chicago to Minneapolis and back, with plans to then go to Boston. On the first two legs, he and first officer Eric Tellman noticed a dirty sock-like smell—an indicator of a fume event—spreading through the Airbus A319 just as they started their descent.
The pilots called for maintenance, who told them there wasn’t an issue to fix. When he objected, Anderberg’s superior told him his protests were delaying the day’s flying schedule. Spirit Airlines didn’t respond to requests for comment.
As they started their third descent, over Boston, the fumes returned.
Starting to feel confused and worried he might pass out, Tellman reached for his oxygen mask. To his left, he saw Anderberg slumped in his seat, his eyes half shut. Tellman forced a mask over his head.
“To be clear: had I not donned my oxygen mask on that July flight, we would have killed every person on that aircraft,” Tellman wrote in a letter to his union detailing the experience.’
‘A year before Anderberg died, Matthew Bass, a 34-year-old British Airways flight attendant was having pizza and drinks with colleagues when he went to lie down and suddenly stopped breathing. In the preceding weeks, he had been inexplicably losing weight, had struggled with coordination, and felt near-constant fatigue.
An autopsy identified inflammation in Bass’s peripheral nervous system and in his heart muscles—similar to Anderberg’s. Both conditions also matched those found in another British Airways crew member, Richard Westgate, a pilot who had died a few years earlier at age 43. Westgate’s family had contended his ill-health was caused by fumes.’
Write to Benjamin Katz at ben.katz@wsj.com
© Wall Street Journal
Professor Dieter Scholz of Aircraft Design and Systems Group (AERO), Hamburg University of Applied Sciences, Hamburg, Germany explains the issue of contaminated air in aircraft in this paper, which he delivered at the Global Cabin Air Quality Executive (GCAQE) Conference in 2021:
Clean Air Campaign -2021 - The Global Cabin Air Quality Executive (GCAQE)
‘The GCAQE is calling on regulators and Governments globally to mandate the introduction of effective 'bleed air' filters and contaminated air warning sensors on passenger aircraft. Exposure to contaminated air can cause a risk to flight safety and to crew and public health.
The aviation industry has known for decades that contaminated air can and has impaired and incapacitated flight and cabin crew. They have also had a good understanding of what chemicals are present during these events for over 20 years.’
Please watch the video in the link below:
https://www.gcaqe.org/cleanair
However, the aviation industry continues to downplay the problem.
They insist that the air in aircraft is safe for everyone to breathe and HEPA filtration is the reason why, as shown here by Airbus in 2021 -page 13:
‘Almost all passenger transport aircraft now use HEPA filters. Airbus and Pall Aerospace have developed a combined HEPA/VOC Filter. VOCs and SVOCs normally come from hydrocarbon based fuels, oils or fluids. They can come from exhaust fumes at the airport, or from aircraft’s own systems in the event of a fault or leakage.’
And
‘HEPA Filters used in Airbus Aircraft remove 99.9% of micro/nano particulates, viruses and bacteria.’
These claims are technically misleading because HEPA and HEPA+carbon filters are not located in the bleed-air supply line and therefore cannot prevent initial inhalation of contaminants.
This article was published by Lufthansa in January 2021:
‘In order to further improve the air quality on board, all A320 aircraft of the Lufthansa Group airlines will be equipped with the best carbon filter technology currently available.
Odors play an important role in the air quality in the cockpit and cabin of an aircraft, also known as "Cabin Air Quality". The perception of an odor says nothing about possible concentrations of hazardous substances, is very subjective and is therefore perceived differently by each person.
The "Advanced Cabin Air Filter" from the manufacturer Pall ensures improved cabin air quality compared to previous filters. In addition to dust, fibers, allergens and viruses, it also filters volatile organic compounds such as exhaust fumes, vapors and odors.
In future, more substances will be filtered out of the cabin air, odor peaks will be eliminated and the duration and intensity of odors will be limited. This ensures greater comfort on board. The roll-out of the new generation of filters is scheduled to be completed by the end of 2024.
https://business.lufthansagroup.com/ge/en/news/carbon-filter-technology
‘The perception of an odor says nothing about possible concentrations of hazardous substances, is very subjective and is therefore perceived differently by each person.’
- Precisely the reason why sensors and monitoring equipment are required onboard aircraft rather than the ongoing reliance of a multi billion £ industry on the efficiency of the human nose.
Many other airlines have installed these ‘Advanced Cabin Air Filters’ from Pall Aerospace, but even with the new HEPA + carbon (A-CAF / HPAC) filters, the inhalation-before-filtration problem still exists — because of how aircraft ventilation systems work and where the filters are located.
On all bleed-air aircraft (Airbus and Boeing):
Bleed air → mixes with recirculated cabin air → THEN passes through the recirculation filter.
This means:
Passengers and crew breathe the contaminated air before it ever reaches the HEPA or HEPA+carbon filter.
Why? Because:
- The filter is not in the bleed-air line
- It is only in the recirculation loop
- There is no filter at all on the engine/APU bleed-air supply
- So even if Pall’s HEPA & Carbon filters captured everything perfectly, you still inhale the contaminants first.
This fundamental design flaw has not changed.
No HEPA or HEPA+carbon upgrade can eliminate this exposure.
This is technically undeniable.
Electrostatic conditioning of aerosols inside aircraft
As aerosols travel from the engine through hot ducts and aircraft ventilation components, they undergo:
- contact charging against positively charged surfaces
- ion attachment from positively charged ions
- retention of charge due to extremely low humidity
Result:
Aerosols that may begin with mixed or neutral charge at the engine become predominantly positively charged by the time they reach the cabin.
This increases biological uptake and cellular penetration of toxic aerosols, making them more bioavailable and therefore more harmful at far lower concentrations than uncharged particles.
This phenomenon is well understood in aerosol physics when applied to dry, high-static environments and explains why the toxicity of fumes in aerosol form has been severely underestimated and the true nature of fume events can rarely be reproduced on the ground.
Which is another reason why sensors and monitoring equipment onboard aircraft is required.
The aviation industry is well aware of this phenomenon as shown in the project on electrostatic precipitation below.
It states explicitly that Electrostatic Precipitation (ESP) based removal of UFP’s in aircraft cabins is:
- Technically feasible
- Energy efficient
- Effective for sub-100nm nanoparticle
- Superior to HEPA for charged particles
‘This project has received funding from the Clean Sky 2 Joint Undertaking (CS2JU REG-IAD) under grant agreement No. 831963.’
Exploring the potential of electrostatic precipitation as an alternative particulate matter filtration system in aircraft cabins
Bastien Pellegrin, Philippe Berne, Hervé Giraud, Arthur Roussey (2022)
https://hal.science/hal-03681328v1/file/Publi%20ESP-EC2S%202021_BP%20-%20Main%20Document%20.pdf
But if it’s not the intention of that project to use electrostatic precipitation also in the bleed air feed, prior to the air entering the cabin, it won’t solve the problem of bleed air contamination in aircraft cockpits and cabins.
The Clean Sky 2 Project is centred around aircraft emissions, fuel efficiency, decarbonisation and sustainability, not bleed-air contamination.
More on electrostatic precipitation here:
https://www.mdpi.com/2674-0516/2/2/17
Aerosol scientists regularly measure particle charge distribution using standard methods (e.g., aerosol neutralizers, electrostatic elutriators), illustrating that real airborne particles frequently carry net charge.
https://stacks.cdc.gov/view/cdc/205677/cdc_205677_DS1.pdf
It seems Rein Andre Roos (may he rest in peace) was right all along:
https://www.academia.edu/32444219/TOXIC_CABIN_AIR_FUME_EVENTS_ELECTROSTATICALLY_REVISITED
Pall A-CAF filters do not stop exposure to toxic fumes even with activated carbon:
- They only filter recirculated air, not the bleed air from the engines
- They cannot stop contaminants entering the cabin in the first place
- They cannot remove ultrafine charged aerosols efficiently
- They cannot prevent inhalation before filtration
- Constant background exposure still happens, as do fume events.
- This architecture guarantees that any contaminants entering the bleed-air stream are inhaled by passengers and crew before any filtration can occur.
‘There was some good news for air passengers. Ultrafine particle pollution in the cabin was very low when aircraft were at cruise altitude in relatively clean air. On the ground, however, it was a different matter. In the new study, the greatest concentrations of ultrafine particles were measured when passengers were boarding and when aircraft were taxiing. On average, the levels were more than twice those that the WHO defines as high. This polluted air was gradually flushed from the cabin once airborne but it increased again on approach to landing, possibly from high concentrations close to flight paths and downwind from airports. This pattern was also found at the destination airports.’
But it’s not good news for pilots and cabin crew who are constantly exposed to both high and low levels in their working environment.
Neither is it good news for engineers, ramp personnel, baggage handlers and ground staff in general.
Why low-level exposure can be medically more harmful than a single event
Decades of toxicology demonstrate that repeated low-dose exposure to organophosphates and VOC’s (and more recently - ultrafine particles) can cause more severe long-term harm than a single high-dose event. This exposure profile precisely matches the bleed-air system environment experienced by flight crew and frequent flyers.
The body never gets time to recover.
This is where cumulative toxicity becomes devastating - because the damage is caused silently - insidiously.
The industry uses high-level fume events as a smokescreen
They say: “There’s no safety risk because fume events are rare.”
But fume events do occur and the health effects, as explained in the Wall Street Journal, are also devastating for the individuals involved as well as their families, friends and colleagues.
But the real exposure profile for thousands of crew is:
Chronic low-dose organophosphate and ultrafine aerosol inhalation on every flight
This is exactly what the bleed-air system produces
And because it’s:
Invisible, often odourless at low concentrations, along with no indication - due to no monitoring onboard…… it’s overlooked.
Furthermore, a fume event is not an isolated spike, but a peak exposure layered onto chronic exposure.
Here are details of some of the fume events which have been published:
https://www.visionsafe.com/recent-smoke-in-the-cockpit-events/
https://avherald.com/h?search_term=Fumes+&opt=0&dosearch=1&search.x=33&search.y=14
A few scientific articles:
Corelease of Genotoxic Polycyclic Aromatic Hydrocarbons and Nanoparticles from a Commercial Aircraft Jet Engine – Dependence on Fuel and Thrust (2024)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10809754/
The Nature of Particulates in Aircraft Bleed Air Resulting from Oil Contamination
The health effects of ultrafine particles
https://www.nature.com/articles/s12276-020-0403-3
Toxicity and health effects of ultrafine particles: Towards an understanding of the relative impacts of different transport modes
https://www.sciencedirect.com/science/article/pii/S0013935123009878
Page 1 - Effects of aviation on climate and local air quality concerns
Page 28 - The Trojan Horse Effect -
https://www.nanoparticles.ch/2024/2024_ETH-NPC-27_book_of_abstracts_presentations.pdf
Aircraft Emissions - The particles that passengers and crew are forced to breathe from the exhaust of other aircraft and ground equipment, drawn into the ventilation system of aircraft through the engines (bleed-air).
This also has very serious implications for engineers, ramp workers, airport ground staff as well as residents living close to, or on flight paths to airports as previously mentioned in the Guardian article:
Emission and Formation of Aircraft Engine Oil Ultrafine Particles
https://pubs.acs.org/doi/10.1021/acsestair.4c00184
Other articles that may be of interest:
https://www.thecanary.co/long-read/2024/10/01/aerotoxic-syndrome-conference/
https://theecologist.org/2024/feb/15/cancer-causing-aircraft
Everything - HEPA, A-CAF(Carbon), ‘Project Fresh’ as well as the word-play used by the aviation industry such as ‘comfort’, ‘perception’ and the increased use of ‘odour’ is built around a major design flaw - rather than fixing it.
However, a ‘proper fix’, which could have brought an end to the bleed-air contamination problem, also developed by PALL Aerospace, was not supported by Airbus because it would have meant re-certification of their aircraft which they were not prepared to do, so this option is not discussed and remains unavailable:
‘Technology of Tomorrow Available Today
The PUREcabin solution. Watch the video to discover more!
Introducing a technology suite that ensures filtration of all air – bleed and recirculated – and offers real-time system contamination analytics for improved operational efficiency, enabling aircraft operators around the globe to offer the cleanest of cabin air environments.
-Improve maintenance efficiency
-Ensure higher cabin air quality
-Mitigate the effect of cabin odors and fumes’
(Unfortunately, the video no longer works)
https://www.pall.com/en/aerospace/landing/purecabinvideo.html
This means a technically viable solution to eliminate bleed-air contamination has existed but was abandoned solely to avoid aircraft re-certification. This is not a technical failure — it is a regulatory and corporate governance failure.
Here’s a 6 minute video on the PUREcabin solution, kindly uploaded to YouTube by Professor Dieter Scholz:
https://m.youtube.com/watch?v=OZC7IFsGG8M
The aviation industry has had the technical means to prevent contaminated air exposure in aircraft for some time. This solution was presented at the GCAQE conferences in 2017 and 2019.
What has been missing is regulatory enforcement and political will.
We are calling on regulators and governments to mandate real-time contamination sensors and filtration of all bleed air before cabin entry, and to formally recognise Aerotoxic Syndrome as an occupational disease.
Thank you for standing with us.
For further information visit: