A Transavia.com passenger jet prepares to take off at Orly Airport near Paris.

London - A pilot fell asleep while in sole charge of a passenger plane thousands of feet up in the air.

The first officer was left in charge after two and a half hours of a Dutch Boeing 737 flight to Crete when the captain went to the toilet.

When he tried to get back in from the flight deck using the intercom, he got no reply.

When he finally managed to get back into the cockpit, he was shocked to discover his colleague was asleep.

A probe has been launched by budget Dutch airline Transavia into what happened.

Although in the incident happened in September, it was only made public on Thursday by the Dutch safety board (OVV) in a report published on its website.

'After two and a half hours in the air the captain of the Dutch-registered plane left the cockpit to go to the toilet,' the OVV said.

'A little later he wanted to return to the cockpit. When he used the intercom to call the first officer to open the door he got no reaction.

'When he managed to get into the cockpit, he found the first officer asleep.'

In September pilots' groups raised concerns that new flying hours imposed by the EU could lead to precisely this problem.

Under the new rules, pilots could be landing commercial jets after 22 hours awake - including 11 hours flying, plus stand-by time and travel to the airport.

MPs had warned in their original report that 22 hours of wakefulness was ‘an extraordinary figure’ - particularly for night flying - that raised levels of fatigue equivalent to being ‘drunk.’

Transport Secretary Patrick McLoughlin was accused of ‘rolling over to Brussels’ after his department approved the rules despite the concerns raised in a report by the respected Commons’ Transport Select committee.

UK pilots can currently go up to 18 hours without sleep - but more than four out of ten pilots already report nodding off in-flight, of whom a third awoke to find their co-pilot also asleep.

The new rules are expected to be adopted into EU law after mid-2013 and fully implemented by the end of 2015. - Daily Maiil