FERNANDO DE NORONHA, Brazil — An airplane seat, a fuel slick and pieces of white debris scattered over three miles of open ocean marked the site in the mid-Atlantic Tuesday where Air France Flight 447 plunged to its doom, Brazil’s defense minister said.

Brazilian military pilots spotted the wreckage, sad reminders bobbing on waves, in the ocean 400 miles northeast of these islands off Brazil’s coast. The plane carrying 228 people vanished Sunday about four hours into its flight from Rio de Janeiro to Paris.

“I can confirm that the five kilometers of debris are those of the Air France plane,” Defense Minister Nelson Jobim told reporters at a hushed press conference in Rio. He said no bodies had been found and there was no sign of life.

The effort to recover the debris and locate the all-important black box recorders, which emit signals for only 30 days, is expected to be exceedingly challenging.

“We are in a race against the clock in extremely difficult weather conditions and in a zone where depths reach up to 7,000 meters (22,966 feet),” French Prime Minister Francois Fillon told lawmakers in parliament Tuesday .

Brazilian military pilots first spotted the floating debris early Tuesday in two areas about 35 miles (60 kilometers) apart, said Air Force spokesman Jorge Amaral. The area is not far off the flight path of Flight 447.

Jobim said the main debris field was found near where the initial signs were spotted.

The cause of the crash will not be known until the black boxes are recovered — which could take days or weeks. But weather and aviation experts are focusing on the possibility of a collision with a brutal storm that sent winds of 100 mph straight into the airliner’s path.

“The airplane was flying at 500 mph northeast and the air is coming at them at 100 mph,” said AccuWeather.com expert senior meteorologist Henry Margusity. “That probably started the process that ended up in some catastrophic failure of the airplane.”

Towering Atlantic storms are common this time of year near the equator — an area known as the intertropical convergence zone. “That’s where the northeast trade winds meet the southeast trade winds — its the meeting place of the southern hemisphere and the northern hemisphere’s weather,” said Margusity.

But several veteran pilots of big airliners said it was extremely unlikely that Flight 447’s crew intended to punch through a killer storm.

“Nobody in their right mind would ever go through a thunderstorm,” said Tim Meldahl, a captain for a major U.S. airline who has flown internationally for 26 years, including more than 3,000 hours on the same A330 jetliner.

Pilots often work their way through bands of storms, watching for lightning flashing through clouds ahead and maneuvering around them, he said.

“They may have been sitting there thinking we can weave our way through this stuff,” Meldahl said. “If they were trying to lace their way in and out of these things, they could have been caught by an updraft.”

The same violent weather that might have led to the crash also could impede recovery efforts.

“Anyone who is going there to try to salvage this airplane within the next couple of months will have to deal with these big thunderstorms coming through on an almost daily basis,” Margusity said. “You’re talking about a monumental salvage effort.”

Remotely controlled submersible crafts will have to be used to recover wreckage settling so far beneath the ocean’s surface. France dispatched a research ship equipped with unmanned submarines that can explore as deeply as 19,600 feet (6,000 meters).

A U.S. Navy P-3C Orion surveillance plane — which can fly low over the ocean for 12 hours at a time and has radar and sonar designed to track submarines underwater — and a French AWACS radar plane are joining the operation.

France also has three military patrol aircraft flying over the central Atlantic, two commercial ships reached the floating debris, and Brazilian navy ships were en route.

Even at great underwater pressure, the black boxes “can survive indefinitely almost. They’re very rugged and sophisticated, virtually indestructible,” said Bill Voss, president and CEO of the Flight Safety Foundation in Alexandria, Va.

“I would expect they’ll dedicate the rather substantial resources of the French navy to this,” Voss added. “I’ve got to figure this will go quickly. I’m hoping they’ll have stuff up in a month, if not just a few weeks.”

Rescuers were still scanning a vast sweep of ocean. If no survivors are found, it would be the world’s worst civil aviation disaster since the November 2001 crash of an American Airlines jetliner in the New York City borough of Queens that killed 265 people.

Investigators have few clues to help explain what brought the Airbus A330 down. The crew made no distress call before the crash, but the plane’s system sent an automatic message just before it disappeared, reporting lost cabin pressure and electrical failure.

Brazilian officials described a three-mile strip of wreckage, and have refused to draw any conclusions about what that pattern means. But Jack Casey, an aviation safety consultant in Washington, D.C., and former accident investigator for airlines and aircraft manufacturers, said it could indicate the Air France jetliner came apart before it hit the water.

A debris field of that length that is strung out in a rough line rather than in a circle, especially when an airplane comes down from a high altitude, “typically indicates it didn’t come down in one piece,” Casey said. “But it doesn’t have to be a jillion little pieces. It can come down in three or four main pieces, and then the ocean drift takes care of the rest.”

Casey cautioned it’s possible, although less likely, that the plane did not break apart and spread of the debris field is due entirely to ocean drift. Since the disaster happened in violent weather, thunderstorms and deep ocean swells could have scattered the debris during the 32 hours that passed before it was spotted on Tuesday.

“The big thing to understand right now is we don’t know,” said Casey, chief operation officer of Safety Operating Systems LLB. “These are tough airplanes. They don’t just come apart.”