Passengers told of terror in the sky when their Qantas Airways plane suddenly plunged nose-first over Australia, tossing travelers around the cabin, causing fractures, concussions and bruises.

Air safety investigators said Wednesday that instruments aboard the A330-300 warned pilots of a glitch in the stabilization system just before the sudden altitude changes on Tuesday's flight from Singapore to the western Australian city of Perth.

"It was horrendous, absolutely gruesome, terrible, the worst experience of my life," passenger Jim Ford, of Perth, told reporters.

He said he thought he was about to die as he watched unbelted passengers being flung around the cabin.

The plane, carrying 303 passengers and 10 crew, was at 37,000 feet and nearing its destination when the incident occurred. It made an emergency landing in Learmonth, Western Australia, about 680 miles northeast of Perth.

More than 40 people were taken to hospitals for treatment, with 14 seriously injured.

Seven Air Transport Safety Bureau investigators were in Learmonth to study the incident and have quarantined the flight data recorder and cockpit voice recorder. They will also interview the crew and passengers.

Qantas, which has been beset by a string of safety problems in recent months, said it was cooperating with the bureau and also conducting its own investigation.

Julian Walsh, director of the ATSB's aviation safety investigation, told a news conference that the pilots received electronic messages "relating to some irregularity with the aircraft's elevator control system," which helps keep the plane level in flight.

The aircraft then climbed approximately 300 feet before it "abruptly pitched noes down," Walsh said. It was unclear how far the aircraft dropped during the incident.

Walsh said environmental factors, such as turbulence, could also have been at play and that it was "too soon to draw any conclusions as to the specific cause of this accident."

Passengers who were not wearing seatbelts flew into the air, some hitting the ceiling of the plane. Loose items scattered throughout the cabin and some overhead luggage compartments flew open.

"It was like a hurricane inside ... like a war zone," Keith Burns, from Lancashire, England, told 2UE radio. "All of a sudden it dropped like a brick, a lead balloon and then it leveled off again and a couple seconds later it fell again.

"There were screams and all the interior was breaking all over the place," he said. "It's an experience I wouldn't like to do again."

Qantas and the ATSB said 14 people had serious, but not life-threatening injuries such as concussions and broken bones. Thirty other passengers were treated in hospitals for concussions, minor lacerations and fractures. Another 30 people with minor bruises and stiff necks did not require hospital treatment.

Walsh said the investigation — also including an Airbus investigator — could take months but a preliminary report would be released within 30 days. Investigators will examine flight data recorders, on-board computer systems, air traffic control and radar warnings and weather conditions, he said.

Qantas said it was assisting the ATSB.

"Our primary concern remains the welfare of our passengers and crew on board the flight, and we are focused on doing everything possible to assist them," Qantas chief Geoff Dixon said in a statement.

It was the latest in a string of safety issues to plague the Australian airline since one of its planes was forced to make an emergency landing in the Philippines in July after an oxygen tank exploded on board, ripping a gaping hole in the fuselage.

Other problems since then included a loss of hydraulic fuel that led to an emergency landing on one flight, a failure of the landing gear on another, and detached panels on various planes, all of which prompted a review by CASA.

The review found "signs of emerging problems" in the airline's maintenance of planes, and CASA ordered Qantas last month to improve.

Qantas had previously been known for its strong safety record, having never lost a jet to an accident. It lost a smaller plane in 1951.