Indonesian investigators say the co-pilot of the crashed AirAsia jet was in controls when he struggled to recover the aircraft as stall warnings sounded.

The Airbus A320-200 crashed into the Java Sea Dec. 28, halfway from Indonesia's city of Surabaya to Singapore. All 162 people on board were killed.

Chief investigator of the National Transportation Safety Commission Marjono Siswosuwarno said Thursday that the cockpit voice recording indicated that the co-pilot, French national Remi Emmanuel Plesel, was flying the plane while Indonesia Capt. Iriyanto was monitoring.

Iryanto, who uses one name, was a former fighter pilot with more than 20,500 flying hours, while less experienced Plesel had about 6,000 hours.

Siswosuwarno said the plane was struggling to recover as stall warnings sounded until the end of the recording.