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Air New Zealand is hopeful data gleaned from the black boxes of its Airbus A320 which crashed off the French coast last year may provide an answer to what caused the accident.

The two black boxes from the Airbus which plunged into the Mediterranean off the southern coast off Perpignan on November 28, had produced "usable data" about the crash, overseas news reports said.

The 150-seat A320, considered one of the most reliable workhorses of the commercial aviation industry, disappeared into the sea as it prepared to land at Perpignan Airport without a mayday call.

All seven people on board - the two German pilots and five New Zealanders - died. Six of the seven bodies have been recovered but have still to be identified.

The two black boxes, a flight data recorder and a cockpit voice recorder, were damaged and initially produced few clues.

However, they were sent to the manufacturers in Canada where experts had obtained some data.

Air New Zealand said it welcomed news that data has been extracted from the two black boxes.

It is understood that neither Air New Zealand nor the Transport Accident Investigation Commission (TAIC) which sent a crash investigator to France, have yet been told what data the black boxes contained.

"This is an important step in the investigation process and will hopefully provide insight into the cause of the accident, as well as helping to provide closure for the families who lost their loved ones," Air New Zealand said in a statement.

It said it had nothing further to say and was waiting for further information from the authorities.

TAIC confirmed it was aware of the development but said it also had not been given details of what data had been recovered.

Witnesses to the crash said the Airbus plunged nose first into the sea.

However, the only hard evidence the authorities had, apart from the data from the two black boxes, was the radar track which gave the position of the Airbus, its height, speed and course.

The radar data was not expected to be of any help in determining the cause of the crash.

The two German pilots from XL Airways were doing final assessment flights before the A320 was to be handed back to Air New Zealand after a two-year charter with the German airline.

Most of the wreckage still lies in about 40 metres of water and New Zealand authorities said earlier this week if enough useful information was retrieved from the black boxes to determine the cause of the crash, French authorities may leave most of the wreckage where it lay.