Le Bourget – The Air France jetliner that crashed in the Atlantic between Brazil and West Africa with 228 people on board hit the ocean intact and did not break up in mid-air, the French bureau leading the investigation said Thursday.

A month-long probe into the 1 June disaster also found that defective air speed monitors on the Airbus A330 were "a factor but not the cause" of the crash, the worst in Air France's history.

"The plane was not destroyed while in flight," said Alain Bouillard from the BEA accident investigation agency as it released its first report on the loss of Flight 447 from Rio de Janiero to Paris.

"The plane appears to have hit the surface of the water in flying position with a strong vertical acceleration," he said, adding that the Airbus came down in the water belly-first.

"The plane was intact at the time of impact," Bouillard told a news conference at BEA headquarters in Le Bourget outside Paris.

There had been speculation that problems with the Airbus' airspeed sensors, or pitot tubes, may have caused the plane to stall or fly dangerously fast, causing a high-altitude breakup.

But investigators said that they had ruled out a mid-air breakup after carefully examining the 640 pieces of debris that have been recovered from the crash zone hundreds of kilometres off Brazil's coast.

The airliner's fin was discovered still attached to part of its base structure, further strengthening the view that the plane was all in one piece when it hit the water.

No inflated life jackets were found among the debris, said Bouillard, adding that "the passengers were obviously not prepared for an emergency sea landing."

The lead investigator said the air speed sensors were "one of the factors but it's not the only one" that led to the crash as the plane flew through turbulence.

"It's a factor but not the cause.

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