"It is an element but not the cause," Bouillard told a news conference in Le Bourget outside Paris. "Today we are very far from establishing the causes of the accident."
The Airbus A330-200 plane flying from Rio de Janeiro to Paris went down with 228 people on board in a remote area of the Atlantic, 930 miles (1,500 kilometers) off Brazil's mainland and far from radar coverage.
The BEA released its first preliminary findings on the crash Thursday, calling it one of history's most challenging plane crash investigations.
One of the automatic messages emitted by the Air France plane indicates it was receiving incorrect speed information from the external monitoring instruments, which could destabilize the plane's control systems. Experts have suggested those external instruments might have iced over.
Bouillard said the plane "was not destroyed in flight." "The plane seems to have hit the surface of the water on its flight trajectory with a strong vertical acceleration," he said, adding that investigators have found "neither traces of fire nor traces of explosives."
Bouillard said life vests found among the wreckage were not inflated, suggesting the passengers were not prepared for a crash landing in the water. The pilots apparently also did not send any mayday calls.
A burst of automated messages emitted by the plane before it fell gave rescuers only a vague location to begin their search, which has failed to locate the plane's black boxes in the vast ocean expanse. The chances of finding the flight recorders are falling daily as the signals they emit fade. Without them, the full causes of the tragic accident may never be known.
He said the search for the plane's black boxes has been extended by 10 days and will continue through July 10.
The black boxes -- which are in reality bright orange -- are resting somewhere on an underwater mountain range filled with crevasses and rough, uneven terrain.
The remote location, combined with the mystery of what happened to the plane -- the pilots had either no time or no radio frequency to make a mayday call -- makes the inquiry exceptionally challenging.
Bouillard said French investigators have yet to receive any information from Brazilian authorities about the results of the autopsies on the 51 bodies recovered from the site.
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