FERNANDO DE NORONHA, Brazil - Search crews flying over the Atlantic found debris from a crashed Air France jet spread over more than 90 km (55 miles) of ocean on Wednesday, reinforcing the possibility it broke up in the air.

The first Brazilian navy ship was nearing the crash area, about 1,100 km (685 miles) northeast of Brazil's coast, to begin the difficult task of retrieving the remains of the Airbus A330 that mysteriously fell out of the sky two days ago on its way from Rio de Janeiro to Paris.

Air force pilots searching the area have reported no signs of survivors or even bodies of any of the 228 people on board flight AF 447. French officials said they may never discover why the plane went down as the flight data and voice recorders may be lost at the bottom of the ocean.

The newly spotted debris included various objects spread across a 5-km (3-mile) area, one metallic object seven meters (23 feet) in diameter and a 20-km (12-mile) oil slick.

The plane sent no mayday signals before crashing, only automatic messages indicating electrical faults and a loss of pressure.

If the decompression reading was correct, it caused a structural problem ... it is a very violent event that causes pieces to come apart and that explains why the wreckage is spread out so much, said Kirk Koenig, a commercial pilot and president of Indianapolis-based Expert Aviation Consulting.

It's like when you see an Indy 500 race car being hit and pieces start to come off, Koenig said.

With officials struggling to explain how a modern aircraft could have crashed in stormy weather that is routine on the transatlantic route, speculation grew that a bomb could have caused the worst crash in Air France's 75-year history.

The airline said on Wednesday it had received an anonymous telephone warning that a bomb was on a flight leaving Buenos Aires on May 27, four days before the crash. A spokesman said the plane was checked, no bomb was found and the aircraft left an hour and a half late. He added that such alerts were relatively common.

Air France, government officials and aviation specialists have said bad weather or a faulty flight control system could be behind the disaster, but have refused to rule out other causes, including terrorism.

Given the challenging location of the crash, its cause may never be known.

I am not totally optimistic. We cannot rule out that we will not find the flight recorders, said Paul Louis Arslanian, the head of France's air accident investigation agency.

MINI-SUB ON ITS WAY

France is dispatching a mini submarine that can explore to a depth of 6,000 meters (19,680 feet) and will try to locate the Airbus's flight data and voice recorders, which should shed light on a crash that has puzzled aviation experts.

The recorders are designed to send homing signals for up to 30 days when they hit water, but there is no guarantee they even survived the impact with the sea, Arslanian said.

Brazil is leading its search effort from Fernando de Noronha, a sparsely populated volcanic archipelago and nature reserve with white sand beaches off its northeastern coast. It has mobilized 11 air force planes, four navy vessels with divers and a tanker for the retrieval operation.

Jorge Amaral, a Brazilian air force colonel, said the long strip of metal found on Wednesday was the biggest piece that search crews have seen so far.

We are considering this 7-meter piece to be part of the plane, possibly part of the side, a piece of steel. It could be part of the fuselage or the tail, he told journalists in Brasilia.

The French investigation will have its first report ready by the end of the month, and will be led by Alain Bouillard, who took charge of the investigation into the crash of an Air France Concorde in 2000.

France held an ecumenical religious ceremony for relatives and friends of those on the plane at Notre Dame Cathedral in Paris on Wednesday, attended by President Nicolas Sarkozy.

(Additional reporting by Alonso Soto and Rodrigo Viga Gaier in Rio, Laure Bretton and Clement Guillou in Paris; writing by Stuart Grudgings; editing by Todd Benson and Anthony Boadle.)