What happened
On September 24, 2011, a pilot initiated a test flight from the Günzburg-Donauried landing field. While flying at approximately 2,500 feet north of the airfield, the pilot observed a warning light indicating a drop in fuel pressure. The pilot attempted to rectify the issue by activating the aircraft's secondary fuel pump, which temporarily cleared the warning.
After notifying Günzburg-Info of the situation, the pilot proceeded to land on runway 24 with the engine running at idle. During the final approach, the pilot maintained an increased airspeed of approximately 70 to 80 knots. During this phase, the left wing of the Schmid-Breezer struck a bush at an altitude of about 5 meters. This impact caused the aircraft to yaw left, subsequently striking a beet field with a longitudinal pitch. The aircraft came to rest approximately 8.5 meters from the initial impact point. The pilot sustained one minor injury, and the aircraft was heavily damaged.
The investigation
The BFU examined the aircraft and the fuel system components. The investigation focused on the fuel supply, noting that the aircraft had been refueled approximately three and a half hours prior to the accident. The pilot reported that the fuel drain valve had previously exhibited dripping, though it had been temporarily stopped by tightening the valve.
Microscopic analysis of the drain valve revealed that the sealing ring was twisted and improperly sized for the sealing seat. Testing demonstrated that the valve failed to provide a complete seal, allowing a flow of approximately 81.3 ccm over a four-hour period. While the investigation confirmed the valve's inability to seal perfectly, the exact reason why the fuel tank was completely empty at the time of the accident could not be determined.