It could be months before investigators know whether air turbulence, a computer failure or both caused a Qantas Airbus to drop about 300ft while flying off the coast of Western Australia.
Passengers on the Singapore-to-Perth flight spoke yesterday of their horror as luggage and people were flung against the ceiling during Tuesday's accident, which seriously injured 14 passengers and crew.
Pilots signalled a mayday and turned the plane towards the RAAF base at Learmonth, north of Perth, where it landed 40 minutes later.
One passenger, Jim Ford, said he thought he was about to die.
''It was horrendous, absolutely gruesome, terrible, the worst experience of my life,'' Mr Ford said as he arrived home in Perth.
Those seriously injured had concussion and fractures and 30 more people had possible concussion and cuts requiring hospital treatment.
Another 30 passengers received first aid treatment for minor injuries.
Ben Cave, of Perth, said for a few seconds his life flashed before his eyes.
''We had a major fall and another fall shortly after. I hit the ceiling but I was okay, I only got a few bruises and strains. I just remember seeing that the plane was a mess,'' Mr Cave said.
The Royal Flying Doctor Service and Skywest ferried the injured to hospitals, while the rest of the 303 passengers and 10 crew were flown back to Perth on replacement Qantas aircraft.
The Australian Transport Safety Bureau has sent five investigators to Learmonth where they will be joined by an Airbus flight control specialist and a Civil Aviation Safety Authority officer.
The bureau's director of aviation safety investigation, Julian Walsh, said the plane had been cruising at 37,000ft when the pilots received an electronic alert of an ''irregularity'' with the aircraft's elevator control system which controls its pitch.
Mr Walsh said the pilots reported the aircraft then climbed ''of its own accord'' about 300ft before abruptly pitching nose down and falling, possibly several thousand feet.
Mr Walsh said the crew initially made an emergency ''pan pan'' broadcast to air traffic control advising of flight control computer problems, some injuries among passengers and crew, and requested clearance to land at Learmonth.
''A few minutes later the crew upgraded that broadcast and declared a mayday and advised control of multiple injuries including broken bones and lacerations,'' Mr Walsh said.
He said it was too soon to draw any conclusions as to why it happened but an initial report of the facts would be issued in a month.
''It's important to look at the whole operation of the aircraft, and whilst clearly, the crew referred to some flight control computer issues, it's important to look at the environmental conditions as well because often these things can interact,'' Mr Walsh said.
Qantas chief executive officer Geoff Dixon said the airline would be contacting every passenger and crew member to ensure they continue to be offered assistance.
The incident makes a bad air safety year for Qantas even worse after several incidents forcing emergency landings including an hydraulic fluid leak which forced a 737 to return to Adelaide in August.
Then in July, a Boeing 747 flying from Hong Kong was forced to land in Manila after an oxygen bottle exploded, blasting a suitcase-sized hole in the side of the aircraft.
Bureau investigators will also liaise with their French counterparts BEA, as they examine the five-year-old A330-300's flight data and cockpit recorders, maintenance records and weather conditions.
Captain Ian Woods, of the Australian International Pilots' Association, said air turbulence was not uncommon in the area.
He said most modern aircraft were equipped to handle changes in high-level winds.
More than forty passengers have been hospitalised, fourteen of whom are seriously injured, after an Airbus A330-300 owned and operated by Qantas suddenly departed level flight, hurling people into the airliner's ceiling.

The flight between Singapore and Perth, Australia was cruising at 37,000 feet when a cockpit alert was triggered warning the flight crew of a possible malfunction with the aircraft's elevator, which controls pitch.

The aircraft then performed an uncommanded climb of 300 feet, before nosing down hard and falling an undetermined distance believed to be several thousand feet. During this descent, many of the 303 passengers and 10 crew were thrown against the ceiling, injuring many of them. The flight crew declared 'pan-pan', one level below a full life-threatening emergency, and performed an emergency landing at an air base at Learmonth after informing air traffic control of flight control difficulties and injured passengers.

The injured people were flown to hospital by Royal Flying Doctor Service and Skywest Airlines. The most seriously injured were suffering from broken bones and three people had concussions.

An investigation has been launched. Although such events are often blamed on turbulence, it has been suggested by industry experts that the circumstances of the accident are more in keeping with a computer malfunction. The A330 is a fly-by-wire aircraft.