Both pilots on a Airbus passenger plane were asleep at the same time with the UK-operated aircraft flying on autopilot.
One of the pilots indicated in a report to the UK’s Civil Aviation Authority (CAA) that the pair nodded off after both had only five hours sleep in the previous two nights.
Details of last month’s incident, on August 13, come at a time when UK pilots’ organisation Balpa is unhappy at proposed European changes to flight-time regulations.
A CAA spokesman said: “This was a serious incident but an isolated one. I think lessons will be learnt from this.
“We don’t know why the pilots had so little sleep before this flight. They were taking it in turn to have rest periods, with the one always checking the autopilot and it looks as if both fell asleep at the same time.”
Details of the incident, logged by the CAA as a mandatory occurrence report, were obtained by a news agency which had asked about pilot fatigue.
The CAA did not say which airline was involved nor where the aircraft, an Airbus A330, was travelling.
The report was headed: “Crew suffering from sym-ptoms of severe fatigue.”
It went on: “Reporter (almost certainly the captain) suggests both members of flight crew had only five hours sleep in two nights due to longer duty periods with insufficient opportunity to sleep. Both rested for 20-minute rotations and fell asleep.”
Balpa said: “The EU is proposing more permissive flight safety rules which would allow pilots to be flying aircraft while dangerously fatigued.”
Balpa general secretary Jim McAuslan said: “The CAA has been far too complacent about the levels of tiredness among British pilots and failing to acknowledge the scale of the under-reported problem.”