EMMA VANDORE and GREG KELLER LE BOURGET Bodies recovered in the Air France disaster show multiple fractures in the legs, hips and arms, which suggests the plane broke up in the air, experts claimed last night.

A spokesman for Brazilian medical examiners said post- mortems on a number of the 50 bodies recovered so far showed the fractures.

The description of the bodies and large pieces of the plane recovered point to the jet breaking apart in the air, said Frank Ciacco, a former forensic expert at the US National Transportation Safety Board.

"Typically, if you see intact bodies and multiple fractures - arm, leg, hip fractures - it's a good indicator of a midflight break up," Ciacco said. "Especially if you're seeing large pieces of aircraft as well."

Jack Casey, an aviation safety consultant in Washington, DC, who is a former accident investigator, said reports that some of the victims were found with little or no clothing was significant. "In an in-air break-up like we are supposing here, the clothes are just torn away," he said. "Getting ejected into that kind of windstream is like hitting a brick wall - even if they stay in their seats, it is a crushing effect. Most of them were long dead before they hit the water would be my guess."

Search teams have recovered more than 400 pieces of debris from Air France Flight 447 but investigators still do not know why the plane crashed into the Atlantic.

Paul-Louis Arslanian, head of the French air accident investigation agency BEA, yesterday expressed "a little more optimism" about the investigation as the discovery of so much debris has narrowed the vast search zone off the northeast coast of Brazil.

"We are in a situation that is a bit more favourable than the first days," Arslanian said. "We can say there is a little less uncertainty, so there is a little more optimism."

However, he added: "It is premature for the time being to say what happened."

Rescuers and military search equipment from Brazil, France, the US and other countries are methodically scanning the surface and depths of the Atlantic for signs of the Airbus A330 that crashed on May 31 after running into thunderstorms en route from Rio de Janeiro to Paris. All 228 people aboard were killed.

Arslanian said the debris that has been found came from "all zones" of the plane, but did not describe it in detail or say what proportion of the plane had been retrieved. The wreckage, some in sections so large and heavy that cranes are required to move it, is being collected in Brazil.

"It is almost certain today that the whole plane won't be recovered," he said.

Still missing are the plane's two black boxes and its flight data and voice recorders. The black boxes, which provide information about what happened to the plane before and during the crash, will emit signals for at least another two weeks. After that, the signals will fade.