A busy plane was left flying on autopilot last month, when both pilots fell asleep at the controls in the cockpit.
Officials are refusing to name the airline, only revealing that the Airbus A330 was operated by a British-based airline and the incident took place on August 13.
The pilots were reportedly taking it in turn to take naps, having only had 5 hours sleep over two nights, when one of them woke up to discover that they had both been asleep at the same time, and did not know how long the plane had been unsupervised.
The unnamed pilots voluntarily reported the incident to authorities, who have kept the name of the airline anonymous in a bid to encourage other whistle blowers to come forward.
It is not thought that the pilots will be disciplined, with the problem being blamed on increasingly demanding schedules.
A spokesman for the regulator said:
‘I would be very surprised if any disciplinary action had been taken against these pilots.
‘Perhaps the airline in question may have looked at their rosta or shift system as a result.
‘I would be very surprised if any disciplinary action had been taken against these pilots'
‘In potentially critical safety situations like this, we aim to learn from what happened and ensure it will not happen again.’
He added: 'We don't know why the pilots had 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.'
Whilst most cases of fatigue amongst pilots have been resolved without incident, a 2009 Air France crash which killed all 228 people on board, was partly blamed on the pilot having had only 1 hours sleep the previous night.