What happened
On May 2, 1997, at 14:45, a privately owned Colomban MC 100 was performing a local circuit at La Baule aerodrome. While completing a landing pattern on runway 11, the pilot was transitioning through a tailwind component. During the descent, the pilot reduced engine power to approximately 2,000 RPM.
As the aircraft approached the final segment of the landing, the pilot realized the aircraft was flying too low and attempted to increase power to maintain the necessary glide path. However, the throttle controls became unresponsive, leaving the engine stuck at 2,000 RPM. Unable to reach the runway threshold, the pilot prepared for an off-field landing. During the short final approach, the aircraft struck a low-voltage power line, resulting in damage to both the aircraft and the electrical infrastructure.
The investigation
The investigation focused on the mechanical failure of the engine control system. It was determined that the pilot, who was also the owner of the amateur-built aircraft, had recently modified the throttle control kinematics. Investigators found that the stop mechanism for the throttle control cable sheath had become dislodged. Consequently, the control cable and its outer sheath were moving together as a single unit rather than moving differentially, which prevented the pilot from being able to adjust the engine power.
Findings
- The primary cause of the accident was a malfunctioning throttle control.
- A recent modification to the throttle linkage kinematics led to the failure of the cable sheath stop.
- The movement of the cable and sheath in unison rendered the pilot unable to increase engine RPM during the approach.