(Reuters) - The French first officer of an AirAsia (AIRA.KL) passenger jet that crashed into the sea last month was at the controls just prior to the accident, Indonesia's lead investigator said on Thursday.
Data from the black box flight data recorder has provided the accident probe with a "pretty clear picture" of what happened in the last moments of AirAsia Flight QZ8501, but officials offered few details.
The Airbus (AIR.PA) 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," said head National Transport Safety Committee (NTSC) investigator Mardjono Siswosuwarno, referring to first officer Remi Plesel.
"The captain, sitting to the left, was the pilot monitoring."
Captain Iriyanto, 53, was believed to have taken over control of the aircraft from Plesel when it started to ascend and then descend sharply, officials said.
The cause of AirAsia's first fatal crash, which occurred around 40 minutes into the flight, was still unknown.
Investigators said the cockpit voice and flight data recorders showed that the plane had been cruising at a stable altitude before the accident. The aircraft was in sound condition when it took off, and all crew members were properly certified, they said.
"The plane was flying before the incident within the limits of its weight and balance envelope," Mardjono said. "While the flight crew had valid licences and medical certificates."
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 sea.
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 Organization (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.
On Wednesday 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.