The Airbus A350 that flies itself in case of depressurisation

The Airbus A350-1000 comes with an automatic feature to help if oxygen is cut. Photo / Supplied

The new Airbus A350-1000 has an inbuilt safety feature - it can automatically descend to a safe altitude if the flight crew are incapacitated because of depressurisation.

The loss of oxygen through rapid depressurisation has been responsible for several crashes and is one theory behind the disappearance of Malaysian Airlines' MH370 in 2014.

New A350-1000s are fitted with automated emergency descent, or AED, a system that engages the aircraft's autopilot function to automatically and quickly bring the aircraft to a lower, safer altitude in the event of in-flight cabin depressurisation.

The AED mode is triggered when the cabin pressure falls below a predetermined limit. After alerting the flight crew, the system engages the autopilot to bring the aircraft to a safe altitude if there is no crew reaction within 15 seconds.

The AED's use on the A350-1000 is the first application of its kind in a large commercial aircraft. Work is being done to fit the system to the earlier model A350-900.

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An autopilot laboratory test team engineer for Airbus, Yann Besse, said depressurisation events were extremely rare.

"Our goal was a simple system that provides significant workload alleviation when a rapid descent is required."

In 2005, a ''ghost flight'' crashed outside Athens, killing all 121 people on board, after the Boeing 737's pressurisation system was not switched back to automatic following a check for a reported leak.

Pressure started dropping early into the Cyprus-to-Prague Helios Airways flight. An investigation found that alarms sounded onboard but the pilots, beginning to feel the effects of hypoxia, misinterpreted them.

Greek fighters were scrambled and saw the 737's pilots slumped over their controls and passengers wearing oxygen masks. They saw a flight attendant take the controls but the plane had run out of fuel and slammed into a mountain.

In 1999 a Learjet carrying golfer Payne Stewart and five others crashed in South Dakota after it lost cabin pressure on a flight from Florida to Texas.

The time of ''useful consciousness'' at 35,000 feet is only 30 to 60 seconds without oxygen.