In January 2020, a British Airways flight from Athens to London issued a "Mayday" emergency call when the pilot flying the plane became incapacitated during a "fume event". The airline industry does not reveal how often fume events happen, but according to some estimates they occur every day on airlines worldwide.. They are thought to be caused by air containing chemicals from engine oil passing into the cabin.

Pilots and cabin crew say that sudden fume events and long term low level exposure to toxic cabin air can make them seriously ill. In some cases they claim exposure to affected air has caused premature death.

The industry insists that serious leaks of toxic gas into cockpits and cabins are relatively very rare, given the number of flights each day. And that no causal link between toxic cabin air and health problems has yet been proven.

But the industry faces multiple court cases this year. On File on 4 one representative of the airline industry agrees to face questions on fume events, claims of a lack of transparency and claims that the health of hundreds of pilots, cabin crew and frequent fliers is being affected.

We reveal confidential airline and Coroners' reports in connection with fume events and so called "aerotoxicity". We hear about pilots and crew who say they've been poisoned by toxic cabin air. And from scientists about research being done on potential links between airline cabin contamination and neurological health.

Presenter: Mike Powell