French officials said they might never discover why an Air France aircraft crashed into the Atlantic with 228 people aboard and that they might not even find the plane's black boxes on the ocean floor.

Paul Louis Arslanian, the head of France's air accident investigation agency, said he was not sure that the black boxes would be recovered and said the probe might prove frustrating.

"I am not totally optimistic. We cannot rule out that we will not find the flight recorders," Arslanian told reporters, warning that the inquiry could take a long time to wrap up.

"I cannot rule out the possibility that we might end up with a finding that is relatively unsatisfactory in terms of certainty," he added.

A first report will be ready by the end of the month, with the investigation led by Alain Bouillard, who took charge of the probe into the crash of an Air France Concorde in 2000.

Arslanian revealed few new elements, confirming only that the crew had sent a radio message reporting turbulence as it headed toward the equator and that the plane had later sent a rapid series of automated messages reporting malfunctions.

"For now, there is no indication to suggest that the plane had a problem before its take off," he said.

Meanwhile, Brazilian navy divers rushed today to reach the wreckage of an Air France jet and start pulling debris from the Atlantic Ocean, where the plane with 228 people went down in the airline's worst disaster in its 75-year history.

Four navy ships with recovery equipment and a tanker were headed to a 3-mile strip of water strewn with plane seats, an orange buoy, wiring, hunks of metal and jet fuel stains about 745 miles northeast of the coastal city of Recife.

Rear Admiral Domingos Nogueira said the navy was battling tough weather as officials predicted the hardest task would be finding the flight data and voice recorders that hold clues to why the plane fell out of the sky during a severe storm in the middle of the night.

Distraught relatives who had prayed for a miracle gave up hope as experts were certain that all aboard died on the flight, which left Rio de Janeiro on Sunday night bound for Paris.

"I just want to find my son's body so that he can have a dignified burial," said Aldair Gomes, the father of Marcelo Parente, who was the head of the Rio mayor's cabinet.

So far no bodies have been sighted on flyovers by the air force, which spotted evidence of the catastrophe on Tuesday, allowing the navy to mount a retrieval operation.

"The ships are equipped to arrive and pick up pieces of the Airbus," Nogueira said. "Each ship has two divers on board and smaller ships to throw into the ocean to try and get pieces."

Helicopters would then be used to take wreckage of the Airbus A330 from the ships to a base on the Brazilian archipelago of Fernando de Noronha, 600 kilometres from the crash site.

On Wednesday, armed forces spokesman Christophe Prazuck told Reuters that the French army had no doubt that the debris belonged to the stricken plane.

Officials said the recorders needed to identify the causes of the mysterious crash could be on the ocean floor at a depth of 6,600 to 9,800 feet.

The recorders are designed to send homing signals for up to 30 days when they hit water.

One expert said it could be among the hardest recoveries since the decades-long search to find the Titanic.

Brazilian President Luiz Inacio Lula da Silva said he was confident that the black boxes would be located.

"I think a country that can find oil 6,000 metres under the ocean can find a plane 2,000 meters (6,500 feet) down," he told reporters yesterday in Guatemala, referring to recent oil finds by Brazil's state energy company in ultra-deep waters.

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