The Global Cabin Air Quality Executive heard at its annual conference in London yesterday that at least 3% of airline pilots are flying with degraded physical and mental performance caused by repeated exposure to neurotoxins in the aircraft cabin air, and may actually become incapacitated during flight if their exposure continues.

This assessment was presented to the conference by Dr Michel Mulder, a former KLM airline captain and medical doctor who now specialises in helping pilots whose health has been damaged by their work. He also reported that a KLM internal communication concedes that “incapacitation in the cockpit is a regular occurrence”.

Mulder is the primary expert behind the medical assessment and treatment of British Airways senior first officer Richard Westgate, whose health was seriously impaired and died in December 2012 aged 43. The Westgate case is being examined by a Coroner’s Court in the UK, and the Court has recently demanded that BA and the UK Civil Aviation Authority state what they intend to do to prevent such deaths in future.

Mulder has developed a test programme for pilots that can determine how much their performance has been degraded by organophosphate neurotoxins from engine oil, which are present at low levels in pressurised cabin air, and occasionally at high levels when a “fume event” occurs. He says the test can predict each pilot's risk level, forecasting approximately how long it will be until the affected individual suffers actual incapacitation during a flight.

Mulder has found that the pilots' tested performance corresponds remarkably with the results of blood tests. He has found a correlation between the significant reduction in naturally occurring essential biochemical markers like the enzyme butyrylcholinesterase – which experts relate to the body's immune-system response to organophosphates – and the degree of degradation of physical and mental response.

Annual medical tests that pilots are required to undergo are not designed to detect these defects, says Mulder.