The co-pilot of a Germanwings flight deliberately drove the plane into the French Alps after "rehearsing" the descent on an earlier flight, French civil aviation investigators said on Wednesday.

The BEA crash investigations office said the co-pilot, 27-year-old Andreas Lubitz, had practiced the manouevre on a flight from Duesseldorf to Barcelona without "noticeable effect" before crashing the plane into the mountains on his return, killing all 150 people on board.