France sent a boat to help with the hunt for the flight recorders and a navy officer told AFP that it will probably take several days to locate and recover the black boxes.

The Yemenia Airways Airbus A310 went down Tuesday in the Indian Ocean as it was approaching for landing on the Comoros Islands. A 12-year-old girl was the only survivor of the crash.

"Investigators from the BEA have detected a signal from the flight recorders" of Flight IY 626, said Comoran lead investigator Ali Abdou Mohamed in a statement.

In Paris, the French accident investigation agency BEA confirmed that a signal had been picked up Sunday morning, providing a major breakthrough in the probe to determine the cause of the disaster.

"We expect to pinpoint the location of the black boxes in the coming days," French Lieutenant Commander Christophe Levivier told AFP. "So the recovery of the black boxes will only be possible after several days."

The signal was picked up about 10 to 12 kilometres from Mitsamiouli beach, north of the capital Moroni, said Abdou Said Madi, director of the national civil aviation agency for the Comoros.

"After that we will ask foreign countries to come help us pull the wreckage from the ocean," he told AFP in Moroni, adding that he believed the plane could be lying some 500 to 600 metres deep in the Indian Ocean.

France sent the Beautemps-Beaupres cruiser currently deployed off the Horn of Africa to help with the search before dispatching submarines to recover the black boxes, said Levivier.

The flight recorders are designed to emit a locator beacon for around 30 days. At 37.5 kilohertz, the signal can be picked up by specialized listening devices.

Former pilot Robert Galan said finding the black boxes would help investigators zero in on the cause of the crash. In 90 percent of cases, he said, the data retrieved explains clearly what happened.

Yemenia Airways, the official carrier of Yemen, has suspended some flights to the Comoros following the crash and has come under strong criticism over its safety standards, which it has rejected.

Yemen's civil aviation chief said Sunday that an audiotape of contact between the Airbus and Moroni airport's control tower did not indicate that the pilots did ran into technical problems.

"Nothing in it indicated problems or technical faults being encountered by the plane," the official Saba news agency quoted Hamed Faraj as telling reporters. "This information will be analysed by an investigations team."

Passengers of the ill-fated Yemenia flight took off from Paris and stopped over in Marseille on June 29 aboard a modern Airbus A330 but they switched in Sanaa to the older A310 jet to continue to Djibouti and Moroni.

Protests over 'flying coffins'

France has said a maintenance check in 2007 had revealed several problems on the A310 and that the plane had not flown in French airspace since, but Yemen has rejected claims that the aircraft was unsafe.

France's large Comoran community has held large protests over the crash, drawing 10 000 people onto the streets of the French Mediterranean city of Marseille on Saturday to demand an end to "flying coffins".

Thousands of Comorans marched in central Paris on Sunday behind a large banner that read "Never Again" and demanded that the government in Moroni bar Yemenia Airways from the country.

French President Nicolas Sarkozy has named a former ambassador to Sudan to personally handle requests from grieving families while Comoros President Ahmed Abdallah Sambi has appealed for calm from members of the diaspora in France.

Comorans are observing a 30-day period of national mourning, while 12-year-old Bahia Bakari, whose mother died in the crash, was recovering in a Paris hospital after she was flown back home by a government plane.

Bahia clung to a piece of plane debris for 10 hours before being pulled from the water.

AFP