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[JAKARTA] AirAsia Flight QZ8501 climbed to an unauthorised altitude fast and steep before the aircraft fell into the ocean, Indonesian investigators said in their first description of the last moments of the ill-fated plane.
From a cruising altitude of 32,000 feet, the Airbus Group NV A320 plane ascended to 37,400 feet in 30 seconds as pilots probably tried to avoid bad weather, Ertata Lananggalih, an investigator at the National Transportation Safety Committee, said in Jakarta on Thursday. The aircraft then descended slowly for three minutes before it disappeared, he said.
"The pilots were conscious when the manoeuvre happened," Mr Lananggalih said. "They were trying to control the airplane."
The co-pilot, with 2,247 hours of flying experience, was at the controls and communicating with the ground while the captain, an experienced officer with 20,537 hours of service, was monitoring, said Mardjono Siswosuwarno, the lead investigator of the crash that killed 162 people.
The aircraft, operated by the Indonesian affiliate of Malaysia-based AirAsia, disappeared from radar Dec 28 en route to Singapore from Surabaya.
Indonesia won't release a preliminary report on its investigation into Flight 8501 because fact-findings could change rapidly, Tatang Kurniadi, head of the commission, said on Thursday. Indonesia sent the preliminary findings to all countries involved in the investigation on Jan 28, Mr Kurniadi said.
The pilots had sought permission from the air traffic control to turn left and then to ascend to 38,000 feet from a stable 32,000 feet because of clouds. Four minutes after the request was made, the ground cleared the pilots to let the plane climb to an altitude of 34,000 feet, he said.
Satellite imagines showed storm clouds that reached as high as 44,000 feet, according to investigators.
The aircraft was in "good condition", said Mr Siswosuwarno.
Indonesian authorities have so far recovered only 70 bodies from the search, which still hasn't managed to lift the fuselage of the single-aisle jet. The tail section of the plane has been retrieved. Indonesia's military pulled out of the search this week.
The cockpit-voice recorder played out the pilots' voices and no explosion was heard, Nurcahyo Utomo, an investigator with the committee, said last week. The flight-data recorder captured 1,200 parameters and the voice-recorder captured two hours and four minutes of the aircraft's final journey, the investigators said. The two devices are called the black box. After studying data from the black box, authorities ruled out terrorism as a factor that brought down the plane.
Flight 8501 appeared to have stalled after climbing steeply, Minister of Transportation Ignasius Jonan said earlier this month. A stall is a situation in which the flow of air under the wing is disrupted, causing a loss of lift.
Indonesia has said it intends to shut the agency responsible for coordinating aircraft flight slots in three months. That's after the AirAsia flight took off on a Sunday, without a Ministry of Transportation permit to fly that day.
The government has since suspended the license of AirAsia for that route, found other airlines in breach of permits and removed officials involved from the ministry, AirNav Indonesia and state airport company PT Angkasa Pura 1.
The airline made an administrative error in flying QZ8501 on Sunday, AirAsia Indonesia Chief Executive Officer Sunu Widyatmoko said Jan 13. The carrier didn't inform the Directorate of Air Aviation on the schedule revision, he told parliament in a hearing.