The French first officer of an AirAsia passenger jet that crashed into the sea last month was at the controls at the time of the accident, Indonesia's National Transportation Safety Committee (NTSC) said.

Mardjono Siswosuwarno, head investigator for the NTSC, told reporters the flight data recorder recovered from the bottom of the Java Sea provided a "pretty clear picture" of what happened in the last moments of AirAsia Flight QZ8501. But he did not give details.

The Airbus A320 vanished from radar screens in bad weather on Dec. 28, less than halfway into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore. All 162 people on board were killed.

"The second-in-command, popularly known as the co-pilot, who usually sits to the right of the cockpit. At the time, he was flying the plane," Mardjono said. "The captain, sitting to the left, was the pilot monitoring."

Mardjono said the cockpit voice and flight data recorders showed that the plane had been cruising at a stable altitude before the crash. The aircraft was in sound condition when it took off, and all crew members were properly certified, he said.

"The plane was flying before the incident within the limits of weight and balance envelope," Mardjono said. "While flight crew had valid licences and medical certificates."

NTSC chief Tatang Kurniadi told the same Jakarta news conference that Indonesia had submitted its preliminary report on the crash to the International Civil Aviation Organisation (ICAO) on Wednesday, as required under global aviation rules.

The report, which has not been made public, was purely factual and contained no analysis, he said, adding that the full, final report would take at least 6-7 months to complete.

Indonesia has previously said the aircraft climbed abruptly from its cruising height and then stalled, or lost lift, before plunging out of control into the Java Sea.

Yesterday, Indonesia said the search for dozens of victims still unaccounted for could end within days if no more bodies were found.

A multinational search and recovery operation has found 70 bodies in the Java Sea and had hoped to find more after finding the fuselage of the plane. But days of rough weather and poor underwater visibility hampered navy divers' efforts.