What happened
On July 31, 2011, a Schempp-Hirth Ventus CM motor glider was participating in a gliding competition at the Klippeneck airfield. The flight was part of a triangular course involving Villingen and Horb. During the flight, the pilot experienced deteriorating climb rates, making the competition task difficult.
As the flight progressed, the pilot attempted to deploy the retractable Solo 2350C engine to assist with the flight. However, the engine failed to start. Witnesses observed the aircraft flying over a grain field with the engine extended, while the pilot continued efforts to start the powerplant. During the final approach for an outlanding near Haigerlyoch, the aircraft entered a left-hand turn at an altitude of approximately 20 meters. The aircraft then entered a left-hand spin, striking a meadow. The pilot sustained fatal injuries, and the aircraft was destroyed.
The investigation
The BFU examined several flight data recorders, including a GPS logger and a Flarm device. Analysis of the B-Record showed a loss of approximately 285 meters in altitude during the final 30 seconds of the flight. The investigation also focused on the aircraft's mechanical state and the pilot's actions regarding the engine.
Investigators found that while the fuel tank contained approximately 12 liters of fuel, the fuel lines to the engine were empty. The fuel cock was found in the closed position, suggesting that the engine failed to start due to incorrect or failed operation of the fuel valve. The aircraft's maintenance records were found to be in order, and the weight and balance were within limits.
Findings
- The primary cause of the accident was an aerodynamic stall during a low-altitude turn, which induced a spin that could not be recovered due to the extremely low altitude.
- The deployment of the retractable engine increased drag and degraded the glider's glide performance.
- Turbulence caused by the airflow over the non-functioning engine may have interfered with the pilot's ability to perceive stall warnings.
- The engine failed to start because the fuel valve was closed or not properly operated, leaving the fuel lines empty.