What happened
On March 5, 2001, a Sukhoi 29 aircraft, registration EC-HPX, was performing flight tests near the Ocaña Aerodrome in Toledo, Spain. The flight was part of an acceptance process to obtain a Spanish Certificate of Airworthiness. During a series of maneuvers, the pilot discovered that the rudder control had become blocked in the right position.
After communicating the emergency via radio, the pilot was advised to bail out via parachute. However, the pilot chose to continue the flight, managing the directional imbalance by using left bank to compensate for the rightward yaw. The pilot successfully reached runway 11 and performed a landing; however, due to the lack of directional control, the aircraft veered off the paved surface and came to rest on the adjacent grass area. The pilot was uninjured.
The investigation
The investigation focused on the mechanical state of the flight controls and the aircraft's structural condition. While no external damage was visible on the airframe, inspectors found fractures and cracks on the engine mount.
Upon examining the flight control linkages, investigators traced the path from the pedals through the control cables to the rudder. They discovered that the protective guard on a pulley located near the pilot's seat had been forced and broken. Furthermore, the investigation found that the end of one of the seat harness straps had been caught between the pulley and the control cable. The excess length of the strap, which was not sufficiently secured by its retaining loop, had interfered with the mechanical movement of the rudder system.
Findings
- The primary cause of the incident was the interference of the pilot's seat harness strap with the rudder control mechanism, which caused the rudder to jam.
- The end of the harness strap entered the space between the pulley and the control cable, creating enough pressure to break the pulley's protective guard.
- The existing method for securing excess strap length was ineffective at preventing the material from entering the control path.
- The aircraft was operating under a restricted flight authorization for testing purposes and had not been required to meet full JAR-23 or FAR-23 certification standards for type certification.
Safety action
- REC 13/2003: It is recommended that the Directorate General of Civil Aviation (DGAC) ensure that the design of flight control systems for the Sukhoi 29 and similar aircraft registered in Spain is reviewed to prevent interference, jamming, or crushing caused by occupants or loose objects within the cockpit.