One Dutch plane was left with no one at the controls as its pilot accidentally fell asleep while the co-pilot went to the bathroom.
Transavia, a low-cost Dutch airline, did not release information about the incident until yesterday, but it occurred in September of 2012.
The pilot was left in charge of the Boeing 737 in a flight to Crete while his co-pilot left to use the toilet. When the co-pilot attempted to re-enter the flight deck by alerting the pilot on the intercom, he did not get a reply.
After he managed to get back into the cockpit, he discovered that the pilot had fallen asleep.
The Dutch safety board (OVV) has called the incident "serious" and is currently investigating it.
"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."
This incident comes after pilots' groups raised concerns over new flying hours by the EU that leave some pilots awake for up to 22 hours, including 11 hours of flying and stand-by time.
Pilots in the UK can go up to 18 hours without sleep, but four in ten pilots have already said they fall asleep during flight, a third of which wake up to find their co-pilot also asleep.