According to Indonesian investigators, the co-pilot of AirAsia Flight QZ8501, French national Remi Plesel, was controlling the plane before it crashed.
Authorities said this information came from the flight data recorder, which was retrieved along with the cockpit voice recorder earlier this month.
The plane was carrying 162 people from the Indonesian city of Surabaya to Singapore when it crashed into the Java Sea on December 28.
Only 70 bodies have been recovered.
Mardjono Siswosuwarno, head investigator of Indonesia’s National Transportation Safety Committee (NTSB), said the flight data recorder had provided a “pretty clear picture” of what happened in the flight’s last moments.
Investigators said the plane ascended sharply before dropping, rising from 32,000ft to 37,400ft within 30 seconds, then dipping back to 32,000ft. The process took about three minutes.
Mardjono Siswosuwarno said the plane was “flying before the incident within the limits of its weight and balance envelope” and that the flight crew all had correct licenses and medical certificates.
A preliminary report has been submitted to the International Civil Aviation Organization, but has not been made public. The full report is likely to take about seven months, said the committee’s chief Tatang Kurniadi.
Earlier this week, the military announced it was stopping attempts to retrieve the fuselage from the seabed. Authorities had believed earlier that most of the missing bodies were still in the wreckage but now believe it is empty and too fragile to move.
The civilian National Search and Rescue Agency said on January 28 that it would continue search operations but their efforts could also end by next week if no more bodies are found.