What happened
On July 25, 1998, a Grob G109 motor glider, registration D-KEAN, was participating in a group flight involving eight aircraft. The flight originated in Cremona, Italy, with a planned route through various Swiss and German locations. Due to deteriorating weather conditions, the group diverted from their original path, traveling through several Swiss regions before heading toward Les Eplatures aerodrome for a refueling stop.
During the final approach to runway 06 at Les Eplatures, the pilot determined the aircraft was too low to safely clear obstacles at the end of the runway. In an attempt to regain altitude, the pilot applied full throttle; however, the engine failed to respond, with RPM remaining between 1000 and 1500. To avoid obstacles, the pilot steered the aircraft toward nearby fields. During the landing sequence, the right wing struck an oat field, causing the aircraft to spin to the right and impact the ground on its left landing gear, which subsequently collapsed.
The investigation
The investigation focused on the engine's failure to respond to throttle inputs. While the aircraft's weight and center of gravity were within limits, investigators noted that the fuel consumption during the 3-hour and 37-minute flight was approximately 20% higher than average. At the time of the accident, 10.6 liters of fuel remained in the tank.
Technical examinations of the engine, including the spark plugs and throttle controls, revealed no mechanical anomalies. The carburetor heat was active, and the engine lacked an automatic mixture control. The investigation also considered the environmental conditions, noting high ambient temperatures during the flight.