Two out of three Air France pilots were sleeping minutes before their plane plunged into the sea with the loss of all 228 people on board.

Details of the last moments of Flight 447, which claimed the lives of three Irish doctors, have emerged in a disturbing new investigation into the 2009 disaster.

Published in the October edition of Vanity Fair magazine, it raises questions about safety aboard civilian passenger jets, and the 'culture' of the Air France pilots on board.

Excerpts from recorded conversations between David Robert (37), Pierre-Cedric Bonin (32) and Marc Dubois (58), the captain of the plane, reveal that two of them were asleep when the plane got into difficulty in a tropical storm.

Referring to Mr Bonin, a 'company baby' on the Rio de Janeiro to Paris flight, the piece reads: "With most of the weather still lying ahead and an anxious junior pilot at the controls, Dubois decided it was time to get some sleep."

Chief investigator Alain Bouillard is quoted as saying: "If the captain had stayed in position through the Inter-tropical Convergence Zone, it would have delayed his sleep by no more than 15 minutes, and because of his experience, maybe the story would have ended differently."

"But I do not believe it was fatigue that caused him to leave. It was more like customary behaviour, part of the piloting culture within Air France."

"And his leaving was not against the rules. Still, it is surprising. If you are responsible for the outcome, you do not go on vacation during the main event."

"F***, we're going to crash"

Up until now it was known that Mr Dubois was sleeping off a night in Rio with his girlfriend, an off-duty hostess and opera singer, who was on the doomed Airbus 330.

"I didn't sleep enough last night. One hour - it's not enough," said Mr Dubois, before he went to sleep.

Referring to "the flight-rest compartment, a small cabin containing two berths just behind the cockpit", the article describes how Mr Robert was also "dozing there".

The article continues: "On the night of May 31st 2009, the pilots of Flight 447 certainly did not serve their passengers well."

The plane was suffering from a loss of lift - or a stall - and its airspeed sensors had malfunctioned.

But instead of lowering the plane's nose to deal with the stall, as they should have done according to normal procedures, they raised it.

Mr Dubois finally entered the cockpit 1 minute and 38 seconds after the pitot tubes malfunctioned, but by that time panic was setting in.

Mr Robert said: "F***, we're going to crash! It's not true! But what's happening?".

Soon after, either Mr Robert or Mr Bonin is heard to say: "F***, we're dead" before - four hours and 15 minutes into the flight - it crashes into the Atlantic.

It took two years to retrieve bodies from the bottom of the sea, along with essential records such as the flight's voice recorder.

Air France has denied that its pilots were incompetent, but has since improved training - concentrating on how to fly a plane manually when there is a stall.

Both Air France and Airbus are facing manslaughter charges, with a judicial investigation led by Paris judges underway.