What happened
On Friday, March 21, 2003, a SOCATA TB 10, registered F-GEVI, was conducting a functional check flight following a scheduled 100-hour maintenance inspection. The flight, operated by S.E.F.A., was intended to verify the aircraft's systems after maintenance work had been completed.
During the initial phases of the flight, including engine start, taxi, and takeoff, the pilot reported no abnormalities. However, once the aircraft reached level flight, the pilot attempted to reduce engine power by adjusting the throttle. The engine speed failed to respond to any movements of the throttle lever, remaining stuck at maximum RPM. Faced with the inability to control engine thrust, the pilot decided to return to the aerodrome at Biscarrosse. To mitigate the risk, the pilot shut down the engine by adjusting the mixture control and performed a U-turn approach. The aircraft landed safely without any damage to the airframe or injuries to the two occupants.
The investigation
The investigation focused on the mechanical state of the engine controls following the recent maintenance visit. Upon inspection of the engine, investigators discovered that the throttle control had become disconnected from the carburetor throttle valve. Specifically, the eyelet end, its locknut, the castell nut, and the cotter pin were all missing from the linkage.
It was established that the throttle control had been disconnected from the carburetor during the maintenance visit to facilitate a part replacement. Due to a long lead time for the necessary replacement part, the aircraft was returned to service without the new component being installed. The existing control was reconnected, but the assembly was not secured with the required castell nut and cotter pin.
Findings
- The primary cause of the incident was insufficient verification of maintenance actions following the reinstallation of the throttle control.
- The throttle linkage was left unsecured, lacking the essential locking nut and cotter pin.
- The aircraft was returned to service with a pending part replacement, which led to the improper reassembly of the control mechanism.
- The operator's maintenance program did not require a systematic check of engine controls specifically following this type of maintenance task.