Investigators picked through the charred debris of a Boeing 737-400 that burst into flames after careening off a runway, as forensic doctors struggled Thursday to identify the 21 people killed, many burned beyond recognition.

A top investigator said that the plane's front wheels snapped off as it landed, and that the fire spread from punctured fuel tanks in the right wing.

"We are trying to find out why the wheel broke," Marjdono Siswo Suwarno said.

About 117 dazed and bloodied survivors staggered from the jetliner after it broke through a fence and came to rest in a rice paddy on Wednesday. Most escaped without major injuries, although several suffered burns and broken bones.

Those killed were trapped in the wreckage of the Garuda Airlines plane after it caught fire, sending billowing clouds of black smoke and orange flames high into the air. The plane had been carrying 140 passengers and crew, officials said.

The accident at Yogyakarta international airport on Java island was the third plane crash in as many months in Indonesia, raising urgent questions about the safety of the country's booming airline sector.

At least four Australians were among the dead, Indonesian officials said. One other Australian was feared dead, but her body had not been formally identified yet. Two other people remained unaccounted for.

On Thursday, Australian and Indonesian crash investigators examined the blackened fuselage and other parts of the plane scattered over a brilliant green rice paddy at the end of the runway, taking photos and notes as they worked.

Both of the plane's flight data recorders had been found and would be sent to Australia for analysis, investigators said.

"It is clear there are no indications of sabotage or intentional explosions in this crash as yet," said Joseph Tumenggung, the head of the investigation team.

The U.S. National Transportation Safety Board said it was sending a team to help the Indonesian government investigate the crash.

Alessandro Bertellotti, a journalist with Italian broadcaster RAI, said the plane was going at a "crazy speed" as it approached Yogyakarta airport after a 50-minute flight from the capital, Jakarta.

"It was going into a dive and I was certain we would crash on the ground," Bertellotti told the Italian news agency ANSA. "I was sitting behind the wing. I saw that the pilot was trying to stop it, but it was too fast. It literarily bounced on the strip."

Several survivors said pilots and flight attendants opened emergency exits and directed passengers to them. The evacuation was orderly for the most part, with some passengers able to take their hand-luggage with them.

"A stewardess opened the door behind me and I was among the first people to get out," Bertellotti told ANSA.

Australian forensic experts were helping Indonesian doctors working to identify bodies in the morgue of the city's Sarjito Hospital. Some relatives argued with doctors, demanding permission to take bodies home they thought they recognized before dental or DNA checks were performed.

"I definitely recognize the body of my brother," said Salamun, who goes by a single name. "We asked doctors to bring him home because as Muslims we want him buried immediately, but doctors required dental records of my brother. This bureaucracy is making us crazy."

As of Thursday, the bodies of 16 victims had been identified, doctor Col. Slamet Pornomo said.

The Indonesian government ordered an investigation into the crash, the latest in a series of accidents in the country.

On New Year's Day, a jet plummeted into the sea, killing all 102 people aboard. Weeks later, a plane broke apart on landing, though there were no casualties. There have also been several ferry sinkings, one of which killed 400.

In response, the government has said it would ban commercial airlines from operating planes more than 10 years old, but most experts say maintenance must be improved and the number of flights per day limited.

Some also have called for Transportation Minister Hatta Radjasa to resign.

"He should not be allowed to wash his hands of this," Burhanuddin Napitulu, senior lawmaker from Indonesia's ruling party. "The public has lost all trust. They are too scared to take planes, trains or ferries any more because the disasters are never-ending."

Dozens of airlines have emerged since Indonesia started deregulating the industry in the late 1990s, and the rapid expansion has raised concerns that growth has outpaced the supply of trained aviation professionals, regulatory oversight, parts and ground infrastructure.

Although Garuda has had nine plane crashes in the past 30 years, killing 330, the airline has made strides recently on improving its safety regulations and training pilots, experts said.