A mid-air emergency which left more than a dozen people on board a Qantas jet seriously injured is believed to have been caused by "some sort of systems failure" rather than turbulence.
The plane plummeted hundreds of metres during a flight from Singapore to Perth yesterday afternoon forcing pilots to make an emergency landing at a remote airport near Exmouth.
Qantas says it is too early to speculate on the cause but the West Australian authorities are blaming a systems problem.
Ian Sangston from the Transport Safety Bureau says they want to check the plane's black box recorder as part of their investigations.
"We've already put what's called a protection order on the aircraft and it's flight recorders, in the movies they're called black boxes."
"So we're very interested in taking custody of the flight data recorder and the cockpit voice recorder."
A statement from Qantas said a number of passengers and crew had sustained injuries, including "fractures and lacerations".
WA police said at least 20 passengers and crew aboard QF72 were seriously injured - some with spinal injuries and others with broken bones and lacerations.
They were flown to Perth on five Royal Flying Doctor Service aircraft last night and transferred by ambulance to city hospitals.
Up to 20 other passengers were treated for minor injuries.
Passenger Andrea Hutchins, 39, of Singapore, said some people appeared to be pinned to the ceiling of the plane or suspended in mid-air.
"The plane was dropping quite quickly so they actually stayed in the air and then they came crashing down," she said.
"It was pretty scary.
"The plane was a mess and there was just crap everywhere. A lot of panels in the ceilings had been damaged by the people that hit them.
The Australian Transport Safety Bureau (ATSB) said the aircraft had experienced a "sudden in-flight upset" while cruising in "level flight".
It said most of the injured were travelling in the rear of the aircraft.
"The crew declared a mayday and diverted the aircraft to Learmonth, near Exmouth in WA, where it landed without further incident," the ATSB said in a statement.