PARIS (Reuters) - Relatives of some of the 228 people killed in a Rio-Paris jet crash voiced hope on Thursday that their two-year wait for an explanation may soon be over as experts prepared to open the aircraft's "black box" recorders.
Investigators into the crash of Air France flight 447 over the Atlantic in June 2009 said they were optimistic at least some of the data could be retrieved but interpreting it could take months.
Watched by relatives of some of the crash victims as well as French and Brazilian police, investigators displayed the two, bright-orange voice and data black-box recorders in public for the first time at a crowded news conference.
The recorders from the Airbus A330 aircraft were hauled nearly 4 km (2.5 miles) to the sea surface at the start of May after a lengthy search operation costing $50 million (30 million pounds) and shipped subsequently to Paris, where they arrived on Thursday.
"We have been waiting for 23 months, which is a long time," said Robert Soulas, who lost his daughter and son-in-law in the crash. "We were frustrated during these long months and we hope this is a new departure and things will move more rapidly."
Investigators said they expected to know by Monday whether it would be possible to extract information from the recorders, which were displayed inside tanks filled with demineralised water to prevent them being damaged by exposure to the air.
Police also expect to know within days if DNA identification can be carried out on some 50 bodies French public prosecutor Jean Quintard said had been found among the wreckage.
Two bodies were brought to the surface last week, but investigators said that unless they can extract DNA information to identify them, they will abandon plans to bring up the rest.
"If identification is impossible, we believe the respect accorded to the victims and yourselves demands the bodies remain in their last resting place," Quintard told relatives.
About 50 bodies were also recovered from the water in the weeks following the crash, the worst in Air France's history.
Investigators said any information gleaned from the black boxes would take months to process and there was no certainty they would determine what went wrong before the crash, when the fully-laden passenger jet vanished in an equatorial storm.
But chief investigator Alain Bouillard told Reuters he was confident part of the data could be recovered. "The recorders have several components so I am fairly confident we can get something, but until we open them we cannot say for sure."
Investigators said it would take at least three days to extract copies of the data -- one for the investigation team and another for French prosecutors -- from the thin memory boards housed inside the bright orange capsules.
Even then, deciphering the evidence is likely to involve weeks of work to synchronize the data and voice recordings.
Of the two recorders, the one containing read-outs of data from the aircraft systems is the most crucial to unlocking the cause of the crash. "Without these parameters it will be difficult to understand what happened," Bouillard told Reuters.
In the best case scenario, France's BEA crash investigation authority hopes to issue findings at the beginning of 2012.
The BEA said it would never release the cockpit voice recordings in public but may issue transcripts of pilot conversations if they were needed to understand the crash.
The speeding up of the investigation will bring some comfort to some 2,500 family members from 32 nations but could have legal implications for manufacturers or the airline.
A French judge heading a criminal probe into the crash has placed Airbus and Air France under formal investigation, which falls short of charges but can open the way to a trial.
Bouillard said many key cockpit systems had been recovered but the aircraft's speed sensors, initially cited as a possible factor in the crash, had not yet been found.
The data recorder may shed light on why the Thales-built sensors, or pitot tubes, appeared to give inconsistent readings in maintenance records transmitted automatically from the aircraft shortly before it disappeared.
(Additional reporting by Thierry Leveque; editing by Philippa Fletcher)