"If we can read the two recorders, we'll manage to understand what happened," Toradec said. That will depend on how much of the data has been corroded.
If data is damaged, that will make its recovery more difficult and slow but not necessarily impossible.
The Airbus A330 plunged into the Atlantic while flying from Rio de Janeiro to Paris on June 1, 2009.
Investigators announced they had found the main wreckage in early April on the fourth and final attempt.
The official cause of the disaster remains uncertain, but the crash has been partly blamed on malfunctioning speed sensors used by Airbus.
Air France has been accused of not responding quickly enough to reports that they might be faulty.
The head of French pilot's union SNPL, Jean-Louis Barber, said that the main priority was to find out why the plane crashed.
Pilots "want these black boxes to be able to speak, for the bereaved families, for Air France and for the entire aeronautical community so that such a tragedy is not repeated," Barber said.