What happened
During a flight originating from Chengdu, the crew was executing a descent toward Wenzhou Airport. While the aircraft was at an altitude of approximately 9,000 meters, the flight crew reported mechanical issues involving the control column being positioned too far forward.
At 16:29 local time, while the aircraft was cleared to descend from 1,200 meters to 700 meters, it transitioned into a nose-down attitude. During this period, the crew attempted to deploy the first stage of flaps, at which point the Angle of Attack (AOA) alarm activated in the cockpit. The aircraft subsequently entered an uncontrolled descent and struck an open field. The impact caused the aircraft to disintegrate. There were 61 fatalities among the occupants, though some local farmers sustained injuries from falling debris.
Findings
Investigations into the accident revealed that a non-standard self-locking nut had been used on the bolt connecting the bellcrank to the pull rod within the elevator control system. This component was not the required castle nut equipped with a cotter pin. The improper nut unscrewed from the assembly, causing the loss of the bolt and the subsequent failure of pitch control capabilities.