The black boxes from an Air Algerie flight that crashed in Mali last week, killing all 118 people aboard, arrived in Paris on Monday as France takes the lead in the investigation.
France's transport minister said reviewing the data from the jet could take "weeks."
Flags flew at half-mast in France on Monday as the country began three days of mourning for the victims, which include 54 French nationals.
The last contact made with the MD-83 was the pilots asking to "turn back" en route from Burkina Faso to Algeria. A sandstorm in the area may have played a role in the crash, but no official cause has been determined.
France sent crash experts and 20 police officers to site in the Mali desert to identify the victims and determine the cause of the disaster.
The accident is the worst air tragedy to hit France since the crash of the Air France A330 from Rio de Janeiro to Paris in June 2009.
It was also the third crash worldwide in the space of just eight days, capping a disastrous week for the aviation industry.
On July 17, a Malaysia Airlines plane was shot down in restive eastern Ukraine, killing all 298 people on board.
And a Taiwanese aircraft crashed in torrential rain in Taiwan on last week, killing 48.
