The vast majority of air disasters happen on takeoff and landing, and the crash of an Airbus A320 in mid-flight in the French Alps suggests that something sudden and catastrophic happened, air safety analysts said.
Tom Costello, an NBC News aviation reporter, stressed that it was too early to say for sure. But he said that one possibility was a sudden loss of air pressure, which can be caused in a fracture in the hull.
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Another possibility investigators could consider, he said, is the loss of an engine, although planes like the A320 can fly on a single engine.
A third possibility investigators could consider is that something criminal happened, he said.
Meteorologists said that there were no early signs that weather was a factor in the crash. The skies were relatively clear in the area where the flight, Germanwings Flight 9525, went down on its journey from Barcelona to Dusseldorf, Germany.
The airline said that 150 people were on board.