What happened
On March 24, 2001, at approximately 12:20 local time, a Schleicher ASH 25 MI motorized glider, registration D-KSAG, was performing a local flight from the Serres aerodrome. The aircraft was attempting an autonomous takeoff from runway 36, an unpaved strip measuring 650 meters in length. At the time of the accident, the runway surface had been softened by recent rainfall.
During the takeoff roll, the pilot utilized approximately half of the available runway length before the aircraft failed to gain sufficient altitude and touched back down on the runway. The pilot reported that the aircraft's flaps, which had been initially set to position "5" (a configuration optimized for takeoff), had unexpectedly retracted to position "1" (a configuration optimized for high-speed flight) during the run. Fearing the aircraft would overshoot the runway, the pilot attempted to re-select the takeoff configuration by returning the flaps to position "5" and continued the takeoff attempt. Although the aircraft briefly lifted off, it could not clear a line of trees located immediately beyond the end of the runway. The aircraft was destroyed in the collision. The pilot and one passenger evacuated the aircraft safely after the pilot activated the emergency beacon and closed the fuel cock.
The investigation
The investigation focused on the mechanical behavior of the flap system and the pilot's decision-making during the takeoff sequence. The pilot, an experienced flyer with significant experience in the Alps, believed he had properly locked the flaps in the extended position and suspected they had moved to the retracted position during the takeoff roll. The investigation also examined the environmental conditions, specifically the state of the unpaved runway following recent rain.