The French air accident investigation agency says the co-pilot of the doomed Germanwings flight repeatedly accelerated the plane as he used the automatic pilot to descend the A320 into the Alps.

The BEA agency said in a statement Friday that investigators have begun studying the black box data recorder from the plane, found at the crash site Thursday.

It says an initial reading of the recorder shows that the pilot used the automatic pilot to put the plane into a descent and then repeatedly during the descent adjusted the automatic pilot to speed up the plane.

Based on recordings from the black box voice recorder, investigators say co-pilot Andreas Lubitz locked the pilot out of the cockpit and intentionally crashed the plane. All 150 people aboard were killed.