Now Dr Peter Julu, a consultant neurophysiologist at the Breakspear Clinic in Hertfordshire and Royal London Hospital, has conducted further tests on 18 pilots suffering from so-called Aerotoxic Syndrome - half from the US study and the others independently.
He said: "The only connection I can derive from there is the organophosphate."
'Healthy and safe'
In 2004, the British Airline Pilots Association highlighted two aircraft the BAE 146 and the Boeing 757 as causing the most problems.
A spokesman for BAE said it has trialled a new air filtration system which is currently being fitted to aircraft.
He said: "BAE systems regards the safety of its fleet of aircraft and those who operate them as of the utmost importance.
"The air quality on the BAE 146 has been shown by independent studies to exceed all existing international standards."
A Boeing spokesman said: " It is our belief that air quality on airplanes is healthy and safe.
"This belief is based on a number of studies that show measured contaminant levels are generally low ad that health and safety standards are met."
Professor Helen Muir, of Cranfield University, who has been researching fume events since 2008, said the link was not yet proven.
She said: "There will be organophosphates on the flight deck, but what matters is, are they there in sufficient concentrations to potentially cause harm to people."
The airline industry is awaiting the findings of Professor Muir's research.
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