France has named two examining magistrates to investigate charges of manslaughter relating to the Air Algérie flight AH5017 crash in Mali last Thursday. Radar images show the plane turning back when it ran into bad weather.
France has taken the lead in the investigation, both in the Malian desert, where the plane went down - killing 118 people, 54 of them French - and in France, where the remains of the passengers will be brought.
Two French judges are investigating charges of involuntary manslaughter, caused by error or negligence.
Their investigation will be done in parallel with that of the French civil aviation safety bureau (BEA), the public body that is charged with technical investigations of air accidents.
Radar images recorded in Burkina Faso's capital, Ouagadougou, after the plane took off for Algiers, show the plane turning back shortly after take-off and losing 2,500 metres in a matter of seconds.
But the manoeuvre appears to have made matters worse, taking it deeper into the storm it was apparently trying to avoid, according to Burkinabé officials.
"Perhaps the pilot thought he had completely avoided it and wanted to return on the right so as to start again on its initial itinerary," said General Gilbert Diendéré, who coordinates the Burkina Faso crisis cell. "It was there when this manoeuvre was made that the accident took place."
The plane appears to have plummeted 10,000 metres in three minutes, Diendéré says.
French President François Hollande met families of the victims on Tuesday to give them information about where the plane went down and about the investigation on the ground.
The plane crashed in the Malian desert, near the Burkina Faso border and appears to have disintegrated on impact.
French, Malian and UN troops are on site to secure the area for investigators on the ground, looking for clues and recovering the remains of the dead.