What happened
On April 24, 2020, a pilot was conducting a long-distance FAI triangle flight in a DG-400 motor glider, registration HB-2068. After flying over 600 km during an eight-and-a-half-hour mission, the pilot began losing altitude while flying near Kölliken. At approximately 200 meters above ground level, the pilot attempted to deploy the retractable engine to facilitate a return to the home airfield in Courtelary.
Upon deployment, the engine failed to produce sufficient power, reaching RPMs of less than 5,000. Following unsuccessful attempts to adjust the throttle and choke, the pilot decided to perform an emergency landing in a nearby field. During the final approach, the pilot utilized full airbrake settings. The aircraft touched down before reaching the intended landing area, causing the left wingtip to strike a rapeseed field. This impact induced a rapid rotation around the aircraft's vertical axis, resulting in damage to the tailwheel, ailerons, and flaps. The pilot exited the aircraft without injury.
The investigation
SUST examined the technical state of the DG-400 and the circumstances of the engine failure. The investigation noted that the pilot's attempt to restart the engine occurred at an altitude significantly lower than the manufacturer's recommendation. The flight manual for this aircraft type advises that engine deployment should ideally occur above 500 meters to ensure sufficient time and altitude for troubleshooting.
Investigators also looked into the cause of the power loss. While the engine functioned normally during the initial climb, it failed to reach full power during the emergency. The investigation considered the possibility that fuel contamination from a metal jerrycan used shortly before the flight might have introduced particles into the carburetor. Notably, the operator has since switched to using a plastic fuel canister.
Findings
- The engine power deficiency was the primary factor preventing a successful return to the home airfield.
- The pilot initiated the engine deployment at only 200 meters altitude, which contradicted manufacturer guidelines and left insufficient time to manage the engine malfunction.
- The aircraft's rotation during landing was caused by the left wingtip striking vegetation, creating a significant moment due to the 8.5-meter lever arm.
- The pilot's decision to focus on the landing approach rather than further engine troubleshooting was considered a safety-conscious action that likely prevented a more serious loss of control.