Passengers on flight MH370 died of oxygen starvation hours before the pilot performed a controlled ditching in the Indian Ocean, an author has claimed.

Veteran air accident investigator Ewan Wilson believes all 239 people lost consciousness up to four hours before the Boeing 777 disappeared beneath the waves.

Wilson, the founder of Kiwi Airlines and a commercial pilot himself, says he reached this conclusion after considering 'every conceivable alternative scenario'.

Author Claims: Investigators claim Captain Zaharie Ahmad Shah, pilot of the missing Malaysia Airlines plane, deliberately ditched into the sea

He believes 'the most likely scenario' is that pilot Zaharie Ahmad Shah deliberately depressurised the cabin, thereby depriving those on board of air.

Although oxygen masks would have dropped down automatically from above the seats, supplies are limited to just 20 minutes.

Those unable to grab a mask, including sleeping passengers, would have passed out within the space of a few minutes.

Everyone on board would have slipped into a coma and died shortly after from oxygen starvation, Wilson says.

Conspiracy Theories: With the flight still missing, there are plenty of theories about what happened to MH370 (
Image:
Getty)

Ahmad Shah, who locked his co-pilot out of the cockpit, then performed a controlled ditching in the sea, which would explain why no debris has been found because the plane landed and sank in one piece.

An earlier report from the Australian Transport Safety Bureau (ATSB) also concluded that passengers may have died from hypoxia. And Malaysian authorities previously named Ahmad Shah as their prime suspect.

But the ATSB report contained no new evidence from within the Malaysian Airlines aircraft.

The claims are made in the book 'Goodnight Malaysian 370', the culmination of a four-month study into the incident, which Wilson co-wrote with the New Zealand broadsheet journalist, Geoff Taylor.

Wilson, a qualified transport safety investigator, said: "One of our objectives in writing this book was, in some small way, to convey the human stories of the tragedy.

Search Area: Investigators have been searching this area off the coast of Australia but there's still no trace of the plane (
Image:
Alamy)

"Our other, more important task was to pursue the truth about what really happened; that is one small contribution we felt we could make to this whole, terrible affair.

They believe that Ahmad Shah, who they have concluded was suffering from mental illness, tricked his co-pilot Fariq Hamid into taking a break about 40 minutes after take-off.

Book Claims: The theory is detailed in this new book about the missing flight (
Image:
SWNS)

After locking Hamid out of the cockpit, Ahmad Shah made his last broadcast to air traffic control - "Goodnight, Malaysian 370" - before switching off the aircraft's air-to-ground communication links.

Ahmad Shah would have had three hours' worth of oxygen - plenty enough, the authors believe, to carry out the "final act of his performance".

They conclude that he set a course for the southern Indian Ocean and, after the fuel ran dry, glided the aircraft for a further 100 nautical miles before performing a controlled ditching on the surface of the water.

Wilson, a trained commercial pilot, said: "Ahmad Shah was a man known for his methodical, thorough nature, for his love of the technical, and probably for his ego, too.

"This would have been his final sad act to his family and to the world: 'find this one'."

Video Loading