What happened
On 25 June 1999, an Avid Speed Wing, registration G-BTRC, was conducting a private test flight at Chichester Airfield, Goodwood. The aircraft, a homebuilt two-seat high-wing monoplane, had recently undergone a significant modification involving the installation of a converted 1000cc BMW motorcycle engine to replace the standard Rotax 582 powerplant.
During the takeoff roll on the grass runway, the flight proceeded normally, and the aircraft established a climb at approximately 65 mph. However, roughly 10 seconds into the climb, at an altitude of about 50 feet, the engine suffered an abrupt loss of power. The pilot attempted to lower the nose to maintain airspeed, but the aircraft lacked sufficient height and speed to execute an adequate flare, leading to a heavy landing. The impact caused minor damage to the nose gear and the left main landing gear, though there were no injuries to the pilot.
The investigation
The investigation focused on the performance of the new engine and its modified fuel system. Prior to the accident, the engine had been tested in a nose-up attitude by tilting the aircraft on its main wheels. Following the incident, investigators realized this testing method was inadequate as it did not replicate the actual climb attitude of the aircraft. Subsequent testing, which involved elevating the main wheels on 9-inch pallets to simulate a steeper climb, revealed that the engine lost power and ran roughly after 10 seconds at full throttle.
During these follow-up tests, investigators measured the fuel pressure at the carburetor inlet, which was found to be only approximately 0.3 psi. The investigation also considered whether the centrifugal clutch in the reduction gearbox might have prevented the propeller from windmilling to assist in an engine restart, but evidence suggested the engine conditions did not meet the criteria for the clutch to disengage.
Findings
- The primary cause of the engine failure was fuel starvation.
- The gravity-fed fuel supply was insufficient to maintain adequate pressure at the carburetor inlet during the aircraft's climb attitude.
- Pre-flight testing failed to identify the issue because the aircraft was not tilted at a steep enough angle to replicate the climb conditions.