AIRLINE pilots and passengers are at risk from contaminated cabin air which can incapacitate crew mid-flight and lead to chronic health problems, according to a groundbreaking international study.

Researchers said recognition of aerotoxic syndrome as a genuine occupational disorder was "urgently needed" alongside routine collection of blood and urine samples from crew and passengers following so-called "fume events" on planes.

The study, led by Dr Susan Michaelis of Stirling University and published by the World Health Organisation, warned of a "reluctance by airlines to investigate such events" and a "clear disincentive" among commercial pilots to report adverse health effects and risk having their licence revoked. It is the first study to look at in-depth at aerotoxic syndrome, which the airline industry has long denied exists.

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In a sample of 274 UK-based pilots, they found that 36 had died or had experienced chronic ill health leading to a permanent loss of fitness to fly, while a total of 172 who reported some type of health problem. Diagnoses included chronic fatigue, gastrointestinal problems and neurological disorders.

A second survey examined 15 cabin air quality incidents in Australia, Germany, the UK and US. It found that a third of cases resulted in "full of partial incapacitation" of both pilots, while more than half had led to long-term health problems for at least one crew member. Nine pilots either became unfit to fly or died. Passengers also reported adverse effects in 27 per cent of events.

Dr Michaelis said: “This research provides very significant findings relevant to all aircraft workers and passengers globally. There is a clear cause-and-effect relationship linking health effects to a design feature that allows the aircraft air supply to become contaminated by engine oils and other fluids in normal flight. This is a clear occupational and public health issue with direct flight-safety consequences."

Since 1955, civilian aircrafts - with the exception of the new Boeing 'Dreamliner' - have conformed to a "bleed-air" design which allows organophosphates and other chemicals to flow into the cabin and cockpit, usually at low levels. However, there have been growing concerns about the health danger from "fume events" - larger leaks - and long-term exposure to tiny amounts of oil vapour by pilots and cabin crew.

Professor Vyvyan Howard, co-author and professor of pathology and toxicology at Ulster University, added: "What we are seeing here is aircraft crew being repeatedly exposed to low levels of hazardous contaminants from the engine oils in bleed air, and to a lesser extent this also applies to frequent fliers."

The authors called for an internationally accepted protocol for investigating aircraft fume events. The study comes months after an inquest into the death of BA pilot Richard Westgaterefused to consider the potential role of aerotoxic syndrome. Mr Westgate, 43, died in 2012 after seeking medical help in the Netherlands for "excruciating pain" and symptoms including headaches and fatigue which his family said he blamed on exposure to contaminated cabin air. The coroner ruled in April that Mr Westgate had died after accidentally overdosing on sleeping tablets.

In a statement, the International Air Transport Association (IATA), which represents airlines, said: “The safety of passengers and crew is of paramount importance to the air transport industry. We cannot comment on the specifics of the Stirling University report.

"There have been substantial studies on cabin air quality over recent years which have guided regulators in this area. Regulators monitor cabin air quality to ensure safety and airlines comply with their requirements. Manufacturers, regulators and airlines are constantly looking to improve safety based on scientific evidence.

"As a result, for example, the industry’s accident record shows constant improvement. This report adds to the store of literature on this important issue and regulators, operators and manufacturers will read the Report’s conclusions with great care.”

The European Aviation Safety Agency, the safety regulator for Europe, has previously said that a causal link between exposure to cabin air contaminants and reported health symptoms "is unlikely".