The flight data recorder from the EgyptAir plane that crashed last month has been fully repaired, raising hopes it will help investigators to determine what caused the passenger jet to go down.

Flight MS804 was en route from Paris to Cairo when it crashed in the Mediterranean Sea on May 19, killing all 66 people on board.

The aircraft's flight data recorder, along with the second component of the black box containing sound recordings from the cockpit, was found two weeks ago - but both had broken into several parts and suffered serious damage, which meant consistent readings could not be taken from them.

READ MORE: Timeline - major air disasters

They were sent to France's BEA air safety agency to be repaired, where they arrived on Monday.

The black box recorder "has been successfully repaired ... by the French accident investigation agency laboratory", Egypt’s investigation commission said in a statement on Tuesday.

"Tests have been carried out ... and we can be sure the flight parameters were properly recorded," the investigators added.

"Work to repair the second black box will commence tomorrow."

Manslaughter probe

The announcement came a day after French authorities said they had opened a manslaughter inquiry into the crash, saying that there was no evidence so far to connect it to "terrorism".

Agnes Thibault-Lecuivre, a spokeswoman for the prosecutor's office, told Associated Press that the inquiry was launched as an accident investigation.

She added that authorities are "not at all" favouring the theory that the plane was downed deliberately - though the status of the inquiry could eventually change if evidence emerges to that effect.

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The Egyptian investigation committee is in charge of issuing a final report, but France can also investigate because the plane was manufactured by France-based Airbus and French citizens were among those killed.

Overall, 40 Egyptians, 15 French, two Iraqis, two Canadians and one person from each of Algeria, Belgium, Britain, Chad, Portugal, Saudi Arabia and Sudan were on board the Airbus A320.

The aircraft had been cruising normally in clear skies on an overnight flight when it crashed.

The radar showed that the plane turned 90 degrees left, then a full 360 degrees to the right, plummeting from 38,000ft to 15,000ft before disappearing at about 10,000ft.