Investigation Summary
As Flight 4509 descended toward Wenzhou, the crew began experiencing significant control difficulties. At 9,000 meters, the pilots noted that the steering column was unusually far forward to maintain level flight. By the time they reached 1,200 meters, the column was pushed fully forward, yet the aircraft did not respond with a nose-down attitude, leading the captain to remark that the controls felt disconnected. When the crew extended the first stage of flaps at approximately 1,000 meters, the shift in the center of lift caused the nose to drop abruptly. Because the physical connection between the cockpit and the elevator had been severed by the loss of a critical bolt, the crew could not pull the nose up. The aircraft entered a high-speed dive and stalled. While some witnesses reported the aircraft began to break apart under extreme aerodynamic loads during the dive, the main wreckage impacted a farm field in Rui'an at high speed and exploded.
Final Conclusions
The primary cause was the installation of non-standard self-locking nuts in the elevator control system's pull rod and bellcrank connection. The manufacturer's specifications required castle nuts secured with cotter pins to prevent loosening from vibration. The incorrect nuts eventually vibrated off, leading to the loss of the connecting bolt and total loss of pitch control. This accident, following another Tu-154 crash in 1994, led the Civil Aviation Administration of China to permanently retire the Tu-154 from all Chinese commercial service by late 2002.
Video Analysis
China Southwest Airlines Flight 4509 | The Plane that Disobeyed the Pilots — An analysis of the maintenance failure that led to the loss of pitch control and the subsequent crash of a Tupolev Tu-154 in China.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Systems & Failure Modes
Elevator Control System
The mechanical linkage between the cockpit steering column and the tail elevators, which failed when a connecting bolt fell out.
Angle-of-Attack Warning
A cockpit alert that triggered as the aircraft entered a stall during its final uncommanded descent.
Interesting Facts
- 01The aircraft was a Tupolev Tu-154M built in 1990.
- 02Incorrect self-locking nuts were used in the elevator control system instead of specified castle nuts with cotter pins.
- 03The failure of the elevator linkage rendered the aircraft's pitch channel completely uncontrollable.
- 04Seven people on the ground were injured by flying debris from the crash.
- 05The crash site was located in a farm field in Baishu village, Rui'an.
Safety Actions & Advisories
Tu-154 Fleet Retirement
Following this accident and the 1994 crash of Flight 2303, Chinese authorities decided to phase out all Tupolev Tu-154 aircraft from commercial service, completed by October 30, 2002.