The China Eastern Airlines Corp. jet was flying a normal route to Guangzhou when it suddenly nosed over at cruise altitude and dove.
That's about all that is known for certain about the unusual crash that feared killed all 132 people aboard the aircraft on Monday in China's worst commercial aviation accident in more than a decade.
While there have been a handful of crashes in which an airliner plunged from cruising altitude, few, if any, fit the extreme profile of the Boeing Co. 737-800 as it pointed steeply toward the ground, according to veteran crash investigators and previous accident reports.
"It's an odd profile," said John Cox, an aviation safety consultant and former 737 pilot. "It's hard to get the airplane to do this."
As investigators search for the plane's two crash-proof recorders and begin poring over clues, they will be trying to determine why the jet made such an abrupt and severe dive, which sets it apart from earlier accidents.
They will be looking at the weather the plane encountered, whether the pilots made any distress calls, any hints in the wreckage of possible malfunctions and detailed profiles of the crew.