Doomed Air France Flight 447 was not destroyed in flight, but fell "almost vertically" and crashed intact in the Ocean, crash investigators said on Thursday.

French investigators presented their initial findings into what caused the plane to drop out of the sky in the middle of the Atlantic on June 1, prompting one of history's most challenging plane crash investigations.

Lead investigator Alain Bouillard said life vests found in the wreckage were not inflated, and that the search for the plane's black boxes will continue through July 10.

The flight hit the Atlantic intact after it 'went straight down, almost vertically,' he said.

The report said speed sensors were a factor but were not the cause of Flight 447's crash.

Bouillard, of the French accident investigation agency BEA, said the sensors, called Pitot tubes, were not the only factor.

"It is an element but not the cause," he said.

One of the automatic messages emitted by the 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.

All 228 people aboard the plane were killed when it plunged into the ocean en route from Rio de Janeiro to Paris.

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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. The chances of finding the flight recorders are falling as the signals they emit fade. Without them, the full causes of the tragic accident may never be known.

Families of the victims met with BEA and Air France officials at the French Transport Ministry just before the findings were reported, according to Christophe Guillot-Noel, head of an association for victims of Air France Flight 447.

"The families are hoping to have all the facts, above all to be able to avoid this eventually happening again," he said.

"We have just one demand: transparency. We have just one expectation: the truth," he said.

Lacking the crucial evidence the black boxes contain, the BEA's initial findings are based on the automated messages sent by the plane minutes before it lost contact, and clues from the wreckage and the remains of 51 people that have been recovered by investigators.

The search for the Flight 447 black boxes is continuing even though the 30-day mark has past and there is no certainty they are still emitting signals. Brazil has ended the search for more bodies.

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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 challenges of 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.

Investigators should have an easier time recovering debris and clues in the crash of a Yemeni Airbus 310 with 153 people on board that went down Tuesday just nine miles north of the Indian Ocean island-nation of Comoros.

The Associated Press contributed to this report.