Two pilots working for UK airlines have been found to have fallen asleep while in sole charge of passenger planes thousands of feet up in the air.
Both men were left alone in the cockpit when co-pilots left the flight deck, the Civil Aviation Authority has revealed.
The authorities refused to name the airlines, claiming it would breach confidentiality. But the British Airlines Pilots Association said the problem is common.
It revealed 43 per cent of members polled admitted sleeping in the cockpit, and a third woke to find the other pilot asleep.
In one of the incidents uncovered after a Freedom of Information request, the captain left to use the toilet. He then tried to call his first officer on a radio link but got no reply.
The captain used a code to get back in the cockpit and found the pilot ‘slumped over the controls’, The Sun reported.
Another pilot also found himself unable to get back in the cockpit and used the entry code. His first officer had to be shaken awake.
A third pilot also fell asleep, while his plane was on the ground.
Rob Hunter, the union's head of safety, told the Transport Select Committee earlier this year that pilots feared being disciplined if they complained of being tired.
"We commonly receive letters that deal with cases where pilots feel that the process that they then get embroiled in is more fatiguing that the duty itself. It becomes a better option to put up with a bit of fatigue rather then report it," Hunter was quoted by the Daily Telegraph as saying.