By Stella Qiu and Jamie Freed
BEIJING/SYDNEY -China's aviation authority said on Wednesday the black boxes of a China Eastern Airlines Boeing 737-800 jet that crashed last month were badly damaged and it was still recovering and analysing the data to help determine the cause.
The crash, China's first deadly air accident since 2010, killed 132 people when the flight from Kunming to Guangzhou suddenly plunged from cruising altitude and crashed into the mountains of Guangxi on March 21.
In a statement on its preliminary crash report, the Civil Aviation Administration of China (CAAC) did not make public any information from the flight data recorder and cockpit voice recorder that were sent to Washington for analysis.
CAAC said the flight crew were qualified, the jet was properly maintained, the weather was fine, and no dangerous goods were on the plane before the crash. The impact created a crater nearly 3 metres deep and 45 square metres wide.
Part of one winglet was found 12 km (8 miles)away, which experts say indicates it may have been torn off due to the force of the plane's initial dive.
Chinese aviation expert Li Xiaojin said the preliminary findings showed there was no issue with the flight procedures, which meant data from the black boxes would be key to determning the cause of the crash.
"It would at least take a year for them to conclude the investigation," he said.
The last normal call from air traffic controllers to the plane was at 2:16pm local time while it was cruising at 8,900 metres (29,200 feet), less than five minutes before the plane began to deviate from its normal path as tracked by controllers in Guangzhou, the CAAC statement said.
At 2:21pm, the last information recorded on radar before the signal disappeared had the plane at an altitude of 3,380 metres (11,100 feet) and a ground speed of 1,010 km per hour (627 miles per hour).
Flight tracking website FlightRadar24's last data, recorded nearly a minute later, had the plane at an altitude of 3,225 feet and a ground speed of 376 miles per hour.
CAAC's statement said it had completed the preliminary report, which according to international rules must be filed to United Nations aviation agency ICAO within 30 days, but does not need to be released publicly.
China Eastern, which grounded its entire fleet of 223 737-800 planes after the crash, resumed commercial flights using the aircraft type on Sunday. The CAAC statement did not point to any technical recommendations regarding the model, which has a strong safety record.
The 737-800 is a predecessor to the 737 MAX, which has not resumed commercial service in China more than three years after two deadly crashes.