Sleepy pilots routinely fall asleep on the flight deck, with a survey by pilots' union Balpa suggesting more than 50 per cent do.
And of the 56 per cent who admitted nodding off, as many as 29 per cent said they awoke to find the other pilot asleep.
Of the 500 commercial pilots polled, 43 per cent said they believed their abilities had been compromised at least once a month in the last six months by tiredness, with 84 per cent saying it has been compromised at some stage during the past six months.
Also, 31 per cent did not believe their airline had a culture that lent itself to reporting tiredness concerns, with only half (51 per cent) saying they believed their airline chief executive would back them if they refused to fly because of tiredness.
Unprompted, 49 per cent said pilot tiredness was the biggest threat to flight safety - three times more than any other threat.
The poll results come ahead of a European Parliament vote on new EU rules on pilot flying hours next Monday.
Balpa believes the new regulations will cut UK safety standards. The union wants MEPs voting on Monday in the EU to back a motion that would require the EC to withdraw its proposals and to subject them to proper scientific and medical scrutiny.
Balpa general secretary Jim McAuslan said: 'Making every flight a safe flight is the number one priority for British pilots who have helped establish some of the highest safety standards in Europe.
"Tiredness is already a major challenge for pilots who are deeply concerned that unscientific new EU rules will cut UK standards and lead to increased levels of tiredness, which has been shown to be a major contributory factor in air accidents."
