What happened
On 13 June 2004, a private flight involving a Stampe SV4C, registration G-AYZI, was conducting a local flight from Sheffield City Airport. Approximately 20 minutes into the mission, while the aircraft was in a 45 to 60 degree right-hand banked turn, the engine began running roughly following an application of full power. The pilot managed to restore normal engine running by reducing the throttle and initiating a return to the airport.
During the subsequent approach to Runway 2le, the aircraft was at roughly 2,000 feet when fuel pressure began to fluctuate alongside changes in engine noise. As the aircraft approached within 3 miles of the runway, the fuel pressure dropped to zero, necessitating a forced landing. The pilot identified a field beyond the initial intended landing site, which featured a standing crop, as a suitable alternative. Upon touchdown, the aircraft struck a surface irregularity, causing the nose to pitch down and resulting in the aircraft coming to rest inverted. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the fuel and ignition systems of the aircraft. They found fuel present in the fuel lines, carburettor bowl, and engine-driven pumps, with approximately 20 litres eventually drained from the tank. No fuel leaks were identified, and the magnetos, spark plugs, and leads were all found to be in good working order. The engine itself showed no evidence of mechanical failure.
Analysis of the fuel state revealed a discrepancy between the pilot's pre-flight visual check of 50 litres and the actual amount present. While the 50-litre estimate would have provided roughly 85 minutes of flight time, the actual amount was lower. The investigation also looked at the aircraft's fuel pick-up system, which utilizes a weighted flexible hose designed to maintain fuel flow during inverted flight.
Findings
- The amount of fuel drained from the tank suggests the pilot's pre-flight estimate of 50 litres was inaccurate, and the actual volume was lower.
- The fuel pick-up hose likely became uncovered due to the combination of a low fuel state and the aircraft's manoeuvring.
- Baffles within the tank may have prevented the flexible hose from accessing the remaining fuel during the banked turn.
- The loss of fuel pressure and subsequent engine failure was likely caused by this intermittent fuel starvation.