Three flights experience fumes in the cabin

Is the bleed air system safe for crew and passengers?

Cabin crew felt unwell

Several flight attendants complained of headaches during a flight aboard an Airbus A330 last week. This was the third instance on an American Airlines plane in the past three months.

In another incident, in October 2016, flight attendants on board a British Airways Airbus A380 had to use emergency oxygen after suspected “toxic fumes” were detected in the cabin.

It is believed by some that the method of introducing air into the cabin adds toxic fumes into the confined space.

The bleed air system

To have a sufficient air pressure to breathe at the altitudes at which jet airliners fly, a supply of warm compressed air is required.

Possible health implications for crew and travellers


Frank Brehany, consumer director, Holiday Travel Watch, began to look into the possible health implications of cabin air in 2006. He said:

“The majority of aircraft that are flying today are powered by engines with a bleed air system.

“When you are sitting in your seat on the aircraft, the air that you are breathing as you look out the window is coming through the engine that is keeping the aircraft aloft.”

This air supply is bled from the compressor sections of the engines, there is no contact with combustion gasses.

There are moving parts which can fail

However, the compressor section has moving parts that need to be lubricated. Most jet engines have “wet seals” to keep the oil and air apart. These are not 100% effective, and can fail over time. If they fail, then oil gets added to the bleed air.

The extremely high temperatures of the engine compartment can cause this oil to break down. The broken-down chemicals are generally hydrocarbon organophosphate in nature.

It was believed by medical experts that sustained exposure to organophosphates contributed to the death of a 43-year-old ­British Airways pilot.

Air cabin air is no more germ-laden than an office

Despite claims of illness while flying, studies have shown that a crowded airplane is no more germ-laden than other enclosed spaces. Researchers at Cranfield University of the UK, found that levels of pollutants were comparable to those typically experienced in domestic settings.

The report noted:

“in over 95% of the cabin air samples, no detectable amounts of TOCP [Tri-ortho-cresyl Phosphate]or other TCPs [Tricresyl phosphates] were found. TBP [Tributyl phosphate] was detected more routinely, but not in the majority of samples. The highest level of TBP recorded was 21.8 µg m-3 (overall mean 1.07 µg m-3) which exceeds any reported domestic indoor air level. TBP levels were highest during first engine start.”

As TBP is in aircraft hydraulic fluid  it is not surprising that the levels found in domestic air was lower than in the sampled cabin air.

The Cranfield University findings are “not a good study”

Brehany said of the report by the university:

“The Cranfield study now not considered to be a good study. There are plenty in the aviation industry who hold it out still, but there are more far more knowledgeable than I who have demonstrated why the Cranfield study can’t be relied on.”

The aviation industry does claim that the air in aircraft cabins matches or is cleaner than the air circulated in public buildings. Indeed, the air is changed more regularly in an aircraft than in a building.  In an Airbus A340-300, the cabin air is completely replaced once every two minutes.

Brehany says that this is not a valid comparison. The public building is not pressurised and the occupants are not at altitude. There are many other reasons why the cabin environment cannot be compared to a building.

“For example, the crew will use chemical toilet cleaners, there will be chemicals emitted off perhaps microwavable products or the holders that they are in, the seats are covered in fire-retardants, the plastic surrounds are full of plasticisers which over time erode and give off organophosphates.

“And that’s aside of anything else you would receive from the air in an aircraft cabin.”

These types of chemicals can be found in any industrial building

It can be said that some of the chemical sources listed by Brehany can be found in a building, but the air pressure at 30ft is not the same as that in an aircraft at 30,000ft.

“Any air quality standard created for aircraft has to be done in relation to the unique environment that it sits in.”

Cabin air is not automatically monitored

Even with all the technology on-board an aircraft, sensors are not used to monitor the cabin air. The only detectors are the passengers and the cabin crew.

The smell from an oil leakage has been described as smelling like a wet dog, smelly socks or vomit. Sometimes there is a bluish haze or smoke in the cabin.

It is only when smoke is visible that the event is officially reported in the flight log. Does this mean that the actual frequency of fume events is under-reported?

“This is where aircrew need to up the ante, they have a responsibility on the aircraft, not on the flight itself, but also the flight after it, they should be making the reports, they’re obligated by law.”

Most aircraft use the bleed air system

Airbus aircraft have featured in the above reports, but they are not the only manufacturer to use the bleed air system. A spokesperson said:

“Airbus aircraft are designed in compliance with all Airworthiness Regulations to provide the highest level of cabin air quality.”

New study

The European Aviation Safety Agency commissioned further research into cabin air quality:

  • In-flight cabin/cockpit air measurements (launched in 2014)
  • Aviation turbine engine oil toxicity (launched in 2015)

There has been delays in completing these reports, but they are currently timetabled to be published in March 2017.

Cranfield University has not responded to requests for comment.