NUCLEAR SUB JOINS AIR FRANCE HUNT
The “black boxes”, which emit a locator signal for about 30 days, could be up to 6,100m (20,000ft) deep, on the bed of the Atlantic.
They could provide vital clues as to why the Airbus A330 crashed on 1 June.
Brazilian air and sea searches have now recovered 41 bodies from the plane, which had 228 people on board.
The submarine, and Brazilian naval and air forces, have a large and remote area of ocean to search.
Debris from the plane, which was flying from Rio de Janeiro to Paris, has been found some 1,000km (600 miles) north-east of the Fernando de Noronha islands. The islands are about 320km off the north-eastern coast of Brazil.
French military spokesman Captain Christophe Prazuck said the submarine – the Emeraude – should be able to cover an area of 26 sq km each day. It has advanced radar equipment on board.
The US is also joining the search, sending two sophisticated listening devices, which will be deployed on two large vessels hired by France. They will be towed in a grid pattern across the search area.
If the aircraft's two black boxes are located, a mini-submarine called the Nautile will be sent down to retrieve them. The vessel, which has a crew of three and is about 8m long, is the same one which explored the wreck of the Titanic.
On Monday, a search team recovered a large tail section. The Brazilian military released photographs of divers securing the tail fin, which was painted in Air France colours.
Officials said the first bodies had been taken by helicopter to the Fernando de Noronha islands.
They will be moved to the Brazilian city of Recife on Wednesday, where a temporary mortuary has been established.
Investigators hope they can use dental records and DNA tests to confirm identities. DNA samples have been taken from relatives of the plane's passengers to help with the process.
Brazilian President Luiz Inacio Lula da Silva says his country will do all it can to retrieve more bodies.
Investigators have so far focused on whether the plane's speed sensors stopped working properly just before it crashed in turbulent weather.
French officials have said the sensors could have iced over, meaning pilots may have flown into a storm without knowing their speed.
The French Transport Minister Dominique Bussereau told French radio that such a situation could have resulted in “two bad consequences for the survival of the plane”.
“Too low a speed, which can cause it to stall, or too high a speed, which can lead to the plane ripping up as it approached the speed of sound, as the outer skin is not designed to resist such speed,” he said.
Air France has said it is stepping up the process of replacing speed monitors on board its Airbus planes.
The company said it first noticed problems with speed monitors a year ago and began replacing them a few weeks before the accident.
But investigators have said it is too early to say what role faulty sensors might have played in the crash.