What happened
On August 2, 2013, a Sportavia-Pützer RF 4D motor glider departed from runway 12 at the Am Kreuzberg glider airfield as part of a flight camp. The takeoff and initial climb proceeded normally. However, at an altitude of approximately 30 meters, the aircraft experienced an abrupt loss of engine power.
In response to the power loss, the pilot initiated a left-hand turn. During this maneuver, the aircraft entered an uncontrolled flight state, described by the pilot as a combination of a slip and a spin. The aircraft subsequently stalled and impacted the ground. The pilot sustained one serious injury, and the aircraft was destroyed.
The investigation
The BFU investigation examined the aircraft, the engine, and the environmental conditions. The pilot was a highly experienced glider pilot with approximately 250 flight hours, including 38 hours in touring motor gliders. The aircraft, a single-seat wooden construction, had undergone its last airworthiness inspection in September 2012 and was within all weight and balance limits.
Investigators found no mechanical defects in the engine or the flight controls. The engine and propeller sustained significant damage during the impact, including a broken propeller blade. The investigation also noted that the aircraft had been parked outside in the sun all day, and the air temperature was approximately 35 degrees Celsius. A note regarding a previous oil leak was found in the cockpit, and the pilot reported experiencing engine sputtering during a brief flight earlier that same day.
Findings
- The primary cause of the accident was the pilot's decision to initiate a turn following the engine failure, which led to an uncontrolled flight state and a stall.
- At such a low altitude, a straight-ahead landing was the only viable option, and several suitable landing sites were available in the departure sector.
- The sudden loss of engine power was likely caused by vapor lock (the formation of fuel vapor bubbles) within the fuel system. Several contributing factors supported this conclusion, including the high ambient temperature, the dark-colored fuel cap absorbing solar heat, and the recent operation of the engine, which could have caused heat soak in the fuel lines.