The two black boxes recovered from the wreckage of Flight MU5735 were severely damaged due to the impact of the crash, and the work of data repair and analysis is ongoing, according to a preliminary investigation released by the Civil Aviation Administration of China on Wednesday.

Flight MU5735 was bound from Kunming, Yunnan province to Guangzhou, Guangdong province on March 21 when it crashed in a mountainous region in Wuzhou, Guangxi Zhuang autonomous region, claiming the lives of all 132 people on board.

According to the investigation, the qualifications of the flight crew, cabin crew and maintenance and release personnel all met the requirements. The airworthiness certificate of the aircraft was valid.

There was no fault report before departure of the flight on March 21.

No cargo declared as dangerous goods was on board, and no abnormalities were discovered on devices along the routes, including navigation and surveillance equipment.

No dangerous weather was forecast, and before the jet deviated from its cruise altitude, no abnormalities were discovered in radio communication or command between the crew and air traffic control.

The last normal call between traffic control and the crew was made at 2:16 pm.

The report said the jet departed from Kunming at 1:16 pm and reached its cruising altitude of 8,900 meters at 1:27 pm. It entered the air traffic control zone of Guangzhou at 2:17 pm. Radar in Guangzhou received a flight deviation warning at 2:20 pm.

The controller called the crew but received no response. The last radar information recorded for the jet was at 2:21 pm－with an altitude of 3,380 meters and speed of 1,010 kilometers per hour. The radar signal then disappeared.

The technology team will continue to investigate the cause of the accident, including in-depth wreckage identification, classification, flight data analysis and experimental verification, the report said.

When black boxes are recovered in fairly good condition, investigators can analyze and produce a report on their content within about three months. It requires data retrieval, decoding and analysis before producing a report. But it can take much longer when they are damaged, said Li Xiaojin, a professor from the Civil Aviation University of China in Tianjin.

According to information disclosed by the CAAC, the exterior of the flight recorder was seriously damaged and the storage units also had a certain degree of damage. But the device remained in relatively good shape.

"It takes time to decode the flight recorder. If the storage units were damaged, it may take longer. After decoding the device, it will provide strong evidence as to the cause of the accident," Zhu Tao, head of aviation safety for the CAAC, said at an earlier news conference.