What happened
On May 7, 2018, a DG-400 motor glider, registration OK-2103, experienced an engine failure shortly after departing from runway 36 at Šumperk airport. The engine failure occurred at an altitude of approximately 49 meters AGL during the initial climb.
The pilot, aware of active airfield traffic including a tow plane on the runway, determined that an immediate landing on the runway was unsafe due to the risk of colliding with other aircraft and ground personnel. To avoid buildings and airport infrastructure, the pilot executed a 120-degree left turn to locate a suitable landing site in a nearby field. During the descent, the pilot configured the aircraft with +6 flaps to manage the glide. However, due to the presence of a significant tailwind and the drag from the extended, non-functioning engine, the aircraft's airspeed dropped to the edge of a stall during the flare.
The aircraft performed a hard landing on its main gear, tailwheel, and the right wingtip. The impact caused the tailwheel to break away and resulted in extensive damage to the right wing, including a torn wing skin and damage to the wing spar near the auxiliary fuel tank.
The investigation
The ÚZPLN investigation focused on the cause of the engine failure and the pilot's handling of the aircraft during the emergency. Investigators examined the fuel system, noting that the engine had been transported in the extended position for approximately five hours prior to the flight, during which it was subjected to vibrations.
Technical analysis of the fuel system revealed that the arrangement of fuel lines and components, such as the diaphragm pump and check valves, could allow for a siphon effect. The investigation looked into whether air had entered the fuel lines during transport, potentially creating an air bubble that disrupted fuel flow during the climb.
Findings
- The engine failure was likely caused by air entering the fuel lines, which may have been triggered by the change in fuel line angle during the climb or the increased fuel demand at full power.
- The pilot's ability to control the aircraft during the landing phase was severely compromised by the combination of a tailwind and the aerodynamic drag produced by the extended, inoperative engine.
- The pilot'made a correct decision in selecting the emergency landing site to avoid obstacles and airfield traffic.
- The aircraft sustained significant structural damage to the right wing and the tailwheel assembly.