FERNANDO DE NORONHA, Brazil (AP) ó Military planes and ships struggled through high seas and heavy winds Wednesday toward the bobbing wreckage of an Air France jet, while an investigator said the black boxes may never be found in the depths of the Atlantic.

Rescue boats from several nations were sailing toward the site to start the recovery as aviation experts tried to determine why the plane carrying 228 people from Rio de Janeiro to Paris on Sunday night ended up in the sea.

An airplane seat, a fuel slick, an orange lifevest and pieces of white debris were spotted Tuesday in the ocean about 400 miles (640 kilometers) northeast of the Fernando de Noronha islands off Brazil’s northern coast.

The floating debris was spread out in two areas about 35 miles (60 kilometers) apart, not far from the path of Flight 447. Brazilian Defense Minister Nelson Jobim said no bodies had been found and there were no signs of life.

The recovery effort is expected to be exceedingly challenging. Storm season is starting in the are and water depths sink down to 22,950 feet (7,000 meters).

Four boats and a tanker ship were en route to the scene but Brazil lacks equipment to scour the ocean floora Brazilian navy spokeswoman said Wednesday. Brazil was leading the search for wreckage, while France took charge of the crash investigation.

“The seas in the area are high, and that is slowing the arrival of our ships,” she said, speaking on condition of anonymity. “We have four divers on the way, but the first of them will not get to the scene until midday Thursday.”

The official said if the black boxes are at the bottom of the sea ó three miles (five kilometers) deep in some nearby areas ó there was nothing the Brazil navy could do as they do not have the special remotely controlled subs needed to withstand the pressure at the ocean’s bottom.

If the black boxes have sunk, she said, “We don’t have the equipment to look for them.”

The sturdy black boxes ó voice and data recorders ó are built to give off signals for at least 30 days, even underwater, and could keep their contents indefinitely.

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), but that ship and another French military ship were not expected to reach the area until the end of the week, French military spokesman Christophe Prazuck said.

In Paris, the head of France’s accident investigation agency, Paul-Louis Arslanian, said he was “not optimistic” that rescuers could even recover the black boxes and investigators should be prepared to continue the probe without them.

“It is not only deep, it is also mountainous,” he said. “We might find ourselves blocked at some point by the lack of material elements.”

The reason for the crash remains unclear, with fierce thunderstorms, lightning or a catastrophic combination of causes as possible theories. France’s defense minister and the Pentagon have said there were no signs that terrorism was involved.

French investigators flew to Rio to work with Air France, Airbus and meteorologists to determine what happened ó and in particular to study a flurry of messages sent in the last few minutes before the plane lost contact.

The crew made no distress call before the crash, but the plane’s system sent automatic messages just before it disappeared, reporting lost cabin pressure and electrical failure.

A French AWACS radar plane and two other French military planes flew Wednesday over the area where debris was found to better narrow down the search zone. A U.S. Navy P-3C Orion surveillance plane ó which can fly low over the ocean for 12 hours at a time and has radar and sonar designed to track submarines ó was also joining the operation.

Arslanian told reporters at Le Bourget airport north of Paris that the investigation was only beginning and was likely to last long. He said investigators didn’t have enough information to determine whether the plane broke up in the air or upon impact with the sea.

In the absence of black box data, investigators were studying the plane’s maintenance and other records.

“For the moment, there is no sign that would lead us to believe that the aircraft had a problem before it took off,” Arslanian said.

He said investigators did not know the exact time of the accident or whether the chief pilot was at the controls when the plane went down. Pilots on long-haul flights often take turns at the controls to remain alert.

A key possibility is some sort of collision with a brutal tropical storm in the area that sent winds of 100 mph (160 kph) straight into the jet’s path.

The man in charge of the investigation, Alain Bouillard, said the French accident agency BEA would submit its first preliminary report by the end of June.

While some experts questioned whether a bolt of lightning was enough to bring down the Airbus A330, Mary Schiavo, former inspector general for the U.S. National Transportation Safety Board, said it was plausible.

“For this plane, the difference could have been if the lightning hit a fuel tank or got inside and took out the electrical system,” Schiavo said on CBS’ “The Early Show. “It’s like an atom bomb.”

Towering Atlantic storms are common this time of year near the equator ó an area known as the intertropical convergence zone. But veteran pilots said it was extremely unlikely that Flight 447’s crew planed to fly right through a killer storm.

“Nobody in their right mind would ever go through a thunderstorm,” said Tim Meldahl, a pilot who has flown internationally for 26 years. “If they were trying to lace their way in and out of these things, they could have been caught by an updraft.”

If no survivors are found, it would be the deadliest crash in Air France’s history, and 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.

On land, hundreds of relatives grieved deeply for those who were lost, a roster that included vacationers, business people, even an 11-year-old boy traveling alone back to England.

Brazil began three days of national mourning Tuesday and French President Nicolas Sarkozy and relatives of the victims were attending an ecumenical service at Notre Dame later Wednesday for the crash victims.

“We will miss your dancing feet,” read a tribute from the Northern Ireland family of Eithne Walls, 29, a dancer-turned-doctor. “We will miss your silliness, your wit and your hugs. We will always hold you in our hearts and you are never truly gone.”

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Emma Vandore reported from Le Bourget, France. Associated Press writers Alan Clendenning and Bradley Brooks in Sao Paulo, Marco Sibaja in Brasilia, Slobodan Lekic in Brussels, Belgium, Shawn Pogatchnik in Dublin and Angela Charlton in Paris also contributed to this report.