More mysterious was the disappearance of another 727 in Africa. It was being used to transport diesel fuel to diamond mines. The owners had numerous financial problems and one day, just before sunset, the plane took off without clearance and with its transponder turned off. It is believed to have crashed in the Atlantic Ocean. One theory, never proven, is that it was stolen so the owner could collect insurance.
"I can't think of a water crash in the jet age that hasn't been solved ," said Scott Hamilton, managing director of aviation consultancy Leeham Co.
The Malaysia Airlines jet had been headed from Kuala Lumpur to Beijing. The 239 people aboard were mostly from China. In Beijing, passengers' relatives have complained that the airline has not been forthcoming with information, and that they've had to rely on news reports.
Some of those reports, however, have led to dead ends. Those false alarms appeared to leave searchers with little to go on.
The flight "was very high up in the air early in the morning, when it was still dark," Azharuddin said. "We have no witnesses on the ground and nobody on the plane can be contacted. The area is over the sea, so it's not as easy as that. There are a lot of constraints."
Whether the plane broke up in midair or crashed into the water, there would be some debris.
If the plane broke up "for some aerodynamic reason, like the wing fell off or there was a depressurization, there'd be big chunks of wing and fuselage all over the place. So it'd be very unlikely that it would just be destroyed and turned to dust," said Smart, the aerospace engineering professor.
He added that much of the wreckage may be at the bottom of the sea, which is 50 to 60 meters (165 to 195 feet) deep in the area where the plane was last detected.
The size of the debris field will be one of the first indicators of what happened, aviation experts say. A large, widespread field would signal the plane likely broke apart at a high elevation, perhaps because of a bomb or a massive airframe failure. A smaller field would indicate the plane probably fell intact, breaking up upon impact with the water.
Discovering the debris can take days.
A week after an Adam Air flight carrying 102 people vanished over Indonesian waters on Jan. 1, 2007, an Indonesian navy ship detected metal on the ocean floor. But it would take another two weeks for the U.S. Navy to pick up signals from the flight data and cockpit recorders, and seven months for the boxes to be recovered. The fuselage remains on the ocean floor, and Adam Air is now defunct.
The Malaysian Airlines jet could be less of a challenge than the Adam Air crash in one respect: It was last tracked over much shallower water.
But for now, the mystery is overwhelming.
"It's hard to imagine what could have caused it with these modern planes," Smart said.
Gelineau reported from Sydney. Mayerowitz reported from New York. Chris Brummitt in Kuala Lumpur and Niniek Karmini in Jakarta contributed to this report.
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