By Adrian Goldberg
BBC Five Live Report
Some crew at a leading budget airline are refusing to fly part of the company's fleet saying poor air quality is putting them and passengers at risk.
Flybe says it is confident that its planes are properly maintained
Crew from Exeter-based Flybe say they are scared to work on the company's British Aerospace 146 fleet.
BBC Radio Five Live Report found there had been 10 leaks of contaminated air into cabins in the last 15 months.
Flybe says it is completely confident that its planes are maintained to the highest industry standards.
The 146 is generally used on domestic flights.
During a trip from Birmingham to Belfast in July, two stewardesses collapsed after being overcome by fumes and all seven crew members had to be taken to hospital on landing.
One was subsequently off work for more than a month.
In a similar incident on the same route in February, the flight crew had to don oxygen masks and abort the flight after just 15 minutes.
Some cabin crew are so alarmed that they are boycotting the 146.
One flight attendant said: "I will not get back on the 146 again. I'm angry that my health has been put at risk."
The view is echoed by one of the company's pilots who said that if he was asked to fly the 146 he would say "go take a walk".
The quality of aircraft air has long been the subject of controversy.
Air is bled off from the engines and cooled before being piped inside the plane, but campaigners say fumes from engine oil can sometimes leak into the air system causing them to be inhaled by crew and passengers.
There are also fears that airline employees could be suffering damage to their health because of long-term exposure to these toxins.
Former Flybe pilot John Hoyte has created the Aerotoxic Alliance to campaign on the issue, after claiming that his own health was worn down by the air he breathed at work.
"Passengers' lives are definitely at risk because they are depending on us to be 100% efficient and we're no way near 100%," he said.
Yet there is no proven link between aircraft air and ill-health, and a recent report by the Committee on Toxicity (CoT) for the government was inconclusive.
One of the contributors to the study was Dr Sarah McKenzie Ross of University College London, an expert in the effect on farmers of organophosphates used in sheep dip.
She notes that similar chemicals are present in aircraft engine oil, and after examining 18 pilots from across the airline industry, she concluded that they showed many of the same symptoms as the affected farm workers.
"We found that they showed evidence of cognitive impairment which was obviously quite alarming," said Dr McKenzie Ross.
"I consider the idea of pilots with cognitive deficits of this nature flying aircraft extremely alarming. I would have serious concerns whether they would be able to cope with an emergency situation."
'Better than standard'
Given the small sample size, these findings can not be taken as proof of a long-term risk to the health of pilots and other crew from aircraft air, so Dr McKenzie Ross is now extending her research to canvas more pilots.
British Aerospace says there has never been a single fatality caused by technical failure on the 146 making it "one of the safest commercial aircraft in operation today".
The company also says that design enhancements since its introduction to service mean "cabin air quality on the BAe 146 continues to be better than the industry standard".
"Issues relating to cabin air quality affect the whole of the aviation industry and have been the subject of a number of independent inquiries both in this country and abroad over the last decade," it says.
And it points out that neither the CoT study nor other investigations have ever found a causal link "between the presence of cabin air contamination and the symptoms complained of by a very small minority of cabin and flight deck crew".
But the CoT study did call for further investigation and the Department for Transport (DfT) is now embarking on more tests due to start by the end of the year.
A DfT spokesman said: "The Committee on Toxicity made a thorough examination of this issue and said that it wasn't possible to conclude whether substances in cabin air (either general or following incidents) cause ill-health in commercial aircraft crews.
"The department takes this issue very seriously and accepted the CoT's recommendation that further work be undertaken as a priority to detect any potentially harmful substances in cabin air."
Flybe, which operates over 100 routes in the UK and Europe, told 5live Report: "Flybe is completely confident that its aircraft are operated and maintained to the highest industry standards.
"In line with many previous public announcements, Flybe took a commercial decision several years ago to reduce the number of aircraft types operated from three to two.
"As a result the BAe 146 fleet will have been withdrawn by February 2008."
5live Report: Cabin Fever is broadcast BBC Radio Five Live on Sunday 21 October at 1130 BST