What happened
On 14 January 2001, a Piper PA-15, registration G-BTOT, was being prepared for taxiing at Fishburn, County Durham, during a private flight. Following refueling, the aircraft had been positioned away from the fuel bowser and turned 90 degrees. To facilitate a single-pilot engine start, the control stick was lashed in the aft position and the main wheels were chocked, allowing the pilot to hand-swing the propeller.
During the starting sequence, the pilot encountered difficulty initiating the engine. After several attempts involving various priming and blowing-out procedures, the engine eventually fired. However, upon starting, the engine accelerated to an abnormally high RPM. As the pilot attempted to move around the right wing to reach the cockpit throttle, the left mainwheel moved over its chock. The aircraft swung right and then accelerated toward a windsock mast.
The left wing struck the mast, causing significant damage to the leading edge. This impact caused the aircraft to pivot, further increasing the engine's RPM. While the pilot managed to avoid being struck by the moving aircraft, the Piper PA-15 eventually collided with a corner of the fuel bowser. The impact involved the right wing, propeller, and landing gear. The propeller blades penetrated the bowser, though no fire occurred, and the impact stopped the engine. The pilot was able to shut off the fuel supply and magnetos.
The investigation
Investigators examined the mechanical state of the aircraft and the circumstances of the ground handling. The investigation established that the engine had accelerated to an unintended high power setting. During a review of aircraft documentation, the pilot discovered a facsimile message sent to insurance syndicate members which noted that the throttle linkage on this model had a tendency to vibrate toward the full power position if the throttle friction nut was not kept tight. This specific warning had not been distributed to all relevant parties.
Findings
- The engine accelerated to an abnormally high speed immediately after starting.
- The throttle linkage had a tendency to move toward a full power position due to vibration.
- The pilot had left the throttle friction at a loose setting.
- The ground conditions were soft, which contributed to the aircraft overcoming the wheel chocks.
- The pilot did not anticipate the high power surge following the successful start.