The French co-pilot was flying the AirAsia flight QZ8501 before it crashed into waters off Indonesia last month, investigators said here Thursday.

Head of the investigators from the National Transport Safety Committee (KNKT) Mardjono Siswosuwarno said: "The second-in-command, known as co-pilot, who usually sits to the right of the cockpit, was flying the plane at the time of crash. The captain, sitting to the left, was the pilot monitoring."

Addressing a press conference at the office of the committee, Mardjono said both the flight data recorder and the voice cockpit recorder indicated that the Airbus A320-200 with 162 passengers and crew on board was flying within the limits of its weight and balance envelope before the crash.

"The plane was on sound condition for flight before the accident, and was flying within the limits of weight and balance envelope. All crew had valid licences and medical certificates," Xinhua news agency quoted Mardjono as saying.