French investigators have announced that they had succeeded in extracting “usable data” from the first black box recovered from the Germanwings Airbus A320 that crashed in the French Alps.

Remi Jouty, head of French air crash investigation agency BEA, said on Wednesday that there was still not “the slightest explanation” at this stage on the reasons for the crash that killed all 150 people on board.

“We have just succeeded in extracting usable data from the cockpit voice recorder,” he said, referring to the black box that records sounds and conversations from the cockpit.

But he said the data had only been retrieved in the last few minutes before his press conference, and investigators had not yet analysed the recordings.

Two photos showed the voice recorder badly damaged, but investigators said it could still provide crucial last-minute information on how the plane crashed.

Jouty ruled out the possibility of an explosion, saying “the plane was flying right to the end,” but could not put forward any other theories.

“At this stage, clearly, we are not in a position to have the slightest explanation or interpretation on the reasons that could have led this plane to descend…or the reasons why it did not respond to attempts to contact it by air traffic controllers,” he said.

He said he was optimistic that the second black box, which records technical flight data, will soon be found given that the debris is spread over a relatively limited area.

French President Francois Hollande said earlier that the casing of the second black box had been found, but not the box itself.

‘Catastrophe’

Earlier, Hollande alongside the leaders of Germany and Spain visited the base of the recovery operation in Seyne Les Alpes.

Hollande and German Chancellor Angela Merkel flew over the crash site to see the devastation for themselves before meeting rescue workers outside the crisis centre set up after the worst crash in France in four decades.

“It is unfortunate that we are not able to carry out any rescue operation, because there were no survivors,” Hollande said in a joint press conference with Merkel and Spanish Prime Minister Mariano Rajoy.

He said that French authorities will try to retrieve the remains of the victims, and to carry out a judicial inquiry to “understand what happened in this catastrophe”.

The Airbus A320, operated by Germanwings, a budget subsidiary of Lufthansa, was less than an hour from landing in Dusseldorf on a flight from Barcelona when it unexpectedly went into a rapid descent.

More than 300 policemen and 380 firefighters have been mobilised to recover the wreckage and bodies from the area that can only be reached by helicopter or by foot.

“It’s a very grim task, and the area is very difficult to reach,” Al Jazeera’s Jacky Rowland, reporting from Seyne Les Alpes, said.

It would take “at least a week” to search the remote site, Lieutenant-Colonel Jean-Marc Menichini said, and “at least several days” to repatriate the bodies.

The 144 passengers were mainly German and Spanish. At least three of victims were from the UK, British Foreign Secretary Philip Hammond said.

Iranian news sites also reported that at least two Iranian journalists were also on board the plane.

It was the first fatal accident in the history of Germanwings, and the deadliest on the French mainland since 1974 when a Turkish Airlines jet crashed, killing 346 people.

In a press conference in Barcelona, top officials of Germanwings and its parent company Lufthansa said the aircraft got a “clean maintenance bill” on Monday and was in “perfectly technical shape” to be able to fly. Al Jazeera