China Southwest Airlines Flight 4509Wednesday February 24, 1999
The aircraft was on a flight from Chengdu to Wenzhou when it crashed into a field while on approach to Wenzhou Airport. Witnesses saw the plane nose-dive into the ground from an altitude of 2,300 feet and explode. A self-locking nut, other than a castle nut with cotter pin as specified, had been installed at the bolt for connection between the pull rod and bellcranck in the elevator control system. The nut screwed off, resulting in bolt loss, which led to the loss of pitch control.