Sustained exposure to organophosphates (OP) from contaminated cabin air contributed to the death of a 43-year-old ­British Airways pilot, a group of medical experts believe.

The findings are likely to increase pressure on the industry to take the issue of sustained crew exposure to ­engine bleed air more seriously. Airlines and governments have previously dismissed suggestions that bleed air can be a factor behind flightcrew falling ill.

The pilot, senior first officer Richard Westgate, started flying professionally in 1996 and worked for various airlines before joining BA in 2007. He died in December 2012 after years of increasingly serious symptoms of sickness that went undiagnosed in the UK, despite reference to 15 different medical consultants.

The symptoms included headaches, loss of memory and numbness in his limbs. He was grounded on full pay in September 2011, and consultation with a neurologist in Amsterdam followed. As a result, extensive medical details of his symptoms before death are on record.

Although no coroner’s inquest has been held into his death, medical experts led by Prof Mohamed Abou-Donia of Duke University Medical School, North Carolina – the world’s leading authority on organophosphate poisoning – have published a study into two autopsies carried out on Westgate, who until his illness was a slim, fit, non-smoking paragliding champion.

Abou-Donia and his colleagues are also investigating the January 2014 death of an unnamed 34-year-old BA airline steward, whose tissue samples indicate degradation that appears identical to the pilot’s case, and is “consistent with organophosphate-induced neurotoxicity”. Both Westgate and the steward died in their beds.

Abou-Donia says Westgate’s case is “one of the worst cases of organo-phosphate [OP] poisoning I have come across”.

“In all my specialised tests for neuro-specific auto-antibodies he was the worst by far,” he says. “The air transport industry constantly overlooks vital components of OP poisoning: the combined effects of multiple compound exposure – repeated low-dosage exposure is just as dangerous as a single large dose (often more so) – and the genetic predisposition to toxicity of the individual’s genes.”

Abou-Donia's latter point is particularly important, as some of the fume events investigated saw one pilot react badly to the neurotoxins while the other was apparently unaffected, which led to confusion.

The potential risks of air contamination have been a sensitive area for some years. While airlines do not deny organophosphates from engine oil additives can be present in the engine bleed air that supplies the cabin, they – and aircraft manufacturers – maintain that this is at a harmless level.

Abou-Donia argues this was not so in Westgate’s case, despite the fact that the pilot had never logged an actual “fume event” during his career.

Frank Cannon, the lawyer acting for the families of both deceased, says the Westgate case is a watershed in this controversy. “They can try explaining one [case] away, but not another and then another,” he says. Cannon adds he has “about 50” cases on his books.

BA says: “It would be inappropriate to comment… on the cause of death of an individual. The safety and security of our customers and crew are of paramount importance to British Airways and will never be compromised.

“Our crew are encouraged to report any possible fume event so that our engineers can investigate it. We would not operate an aircraft if we believed it posed a health or safety risk to our customers or crew.”