A French nuclear submarine with advanced sonar equipment began searching on Wednesday for the flight recorders of an Air France airliner that crashed into the Atlantic last week, the French military said, Reuters reported.
The Emeraude was sent to the area to hunt the "black box" recorders, which may help explain the disaster and which are believed to lie on the ocean floor.
Investigators face a long search for clues to what went wrong when the Airbus A330 jet disappeared on a flight from Rio de Janeiro to Paris killing all 228 people on board, French military spokesman Christophe Prazuck said.
"Up to now, the time frame for the search for victims and debris has been of the order of days or a week. Here, at the very least, it's going to be of the order of weeks or months," he told LCI television.
The Air France flight is believed to have run into trouble when it hit a violent storm midway over the Atlantic Ocean and potential problems with speed sensors have become one of the focal points of the inquiry.
Other causes have not been ruled out, but France's interior ministry said on Wednesday that two passengers whose names had been identified as suspicious turned out not to be a concern. The website of the French weekly L'Express had quoted a French military spokesman as saying the names could be linked to Islamic terrorism.
Brazilian military search teams using planes and ships have recovered 41 bodies and moved 16 of them to the archipelago of Fernando de Noronha off Brazil's northeastern coast, which is being used as a base for the search operations.
Planes looking for bodies and debris have expanded their search to air space controlled by Senegal due to ocean currents in that direction, Brazil's air force said on Wednesday.
France has sent about 400 military personnel, three planes, one frigate with a helicopter, and a research vessel with mini-submarines as well as the nuclear submarine.
In the search zone, where scattered pieces of debris including a large section from the aircraft tail have been recovered, vessels are trying to comb a rugged area of the ocean floor, thousands of meters below the surface.
Prazuck said searchers had taken two weeks to locate the black box recorders after the crash of a Boeing 737 at Sharm el Sheikh in Egypt in 2004, despite much easier conditions.
"That aircraft crashed very close to the coast, there was no doubt about where the accident happened and it took 15 days to recover the black box," he said.
"Here the accident happened 1,000 kilometers (620 miles) from the coast. The situation is very complex."
He said the Emeraude was searching an area of 36 square kilometers (14 sq miles) and the search zone would be changed daily. If the recorders are found, miniature submarines from the Pourquoi Pas, the French exploration and survey ship also deployed to the area, could be used to retrieve them.
The doomed plane sent 24 automated messages in its final minutes on June 1, detailing a rapid series of systems failures.
The speed sensors that gauge how fast an aircraft is flying have become the focus of the investigation after some of the messages showed they provided inconsistent data to the pilots.
Air France said on the weekend it had noticed icing problems on the speed sensors known as pitot tubes in May 2008 and had asked Airbus for a solution. Airbus responded by reaffirming existing operating procedures, according to Air France, which decided to go ahead and change the sensors from April 27. The A330 that crashed had not yet been modified.
Brazil's TAM airline said it had changed the pitot tubes on its entire Airbus fleet in September 2007, after Airbus recommended the change for its short/medium range A320 family. The recommendation about the sensors was optional for long-haul jets such as the A330.