What happened
On 25 July 2001, a Rans S6-ES, registration G-BYMU, was performing a private flight from Barton Airfield in Lancashire. During the initial climb phase, a mechanical failure occurred within the aircraft's engine drive system. One of the two belts in the double belt drive reduction gear failed. The broken belt became entangled with the throttle mechanism, which forced the throttle to the fully open position.
Unable to regulate engine power through the throttle, the pilot was forced to manage power by manually cycling the ignition switch. Following this failure, the pilot decided to return to the airfield to perform an emergency landing. The pilot opted to shut down the engine entirely, executing an engine-off landing. Upon touchdown, the aircraft experienced a bounce. During the subsequent ground contact, the nose landing gear collapsed. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's drive coupling to determine why the belt had failed. The inspection revealed that the belt pulleys were not operating in proper alignment. This misalignment caused uneven tension between the two belts in the system. Further analysis showed that a bolt within the coupling had failed, which permitted unintended movement between adjacent components and subsequently caused wear.
Findings
- The primary cause of the power control issue was the failure of a bolt in the drive coupling, which led to pulley misalignment and uneven belt tension.
- The failure of one belt caused it to entangle with the throttle, rendering the standard throttle control ineffective.
- The nose landing gear collapse occurred following a bounce during the landing phase, potentially exacerbated by the pilot's control inputs during the bounce.