2012 L13 SE Vivat accident near Hradec Králové (OK-4602)

Overview and flight details On 8 July 2012, an Aerotechnik Kunovice L13 SE Vivat motor glider, registration OK-4602, operated by Aeroklub Hořice v Podkrkonoší o.s., was flying east of Hradec Králové when its engine stopped. The aircraft had departed from Hořice v Podkrkonoší with a pilot and one other person on board. The pilot reported that the engine stopped suddenly, without prior signs of irregular operation, while the aircraft was at 150–180 m AGL and 130 km/h. ## Emergency landing and impact After unsuccessful attempts to restart the engine, the pilot selected a field for an off-airfield landing. The aircraft touched down in a course of 358° in a carrot field containing an irrigation pipe system. The pilot described a sudden deceleration after contact with the irrigation piping, followed by the nose sinking into soft ground and the tail rising. The glider then overturned onto its back. Both occupants remained in their seat belts, then created an opening in the canopy glazing and crawled out from under the cabin frame. Neither was seriously injured; both sustained only minor abrasions. ## Aircraft and maintenance findings The L13 SE Vivat was a two-seat, all-metal motor glider with side-by-side seats, built in 1984, serial number 840004, with a total time of 2,939 h 23 min. It was powered by a Mikron IIIB engine, serial number 105, with 597 h 16 min, and a fixed wooden V 218 propeller. The last 100-hour/annual maintenance was performed on 24 April 2012 at 2,902 h 50 min. After the accident, the engine was cleaned and inspected. Ignition cables, spark plugs, and magnetos were found serviceable. The oil system was leak-free and contained 7.5 l of oil. The fuel system and tank were intact, with about 30 l of BA95 Natural petrol. No mechanical deposits or contaminants were found in the tank. However, the fuel filter body contained an increased amount of mechanical contaminants and metal particles. The carburettor float chamber was free of contaminants, but the main jet was blocked by a 1.2 mm piece of silicone rubber. Similar silicone rubber material had been used to seal the mating surface between the carburettor and the engine intake duct. ## Probable cause and analysis The investigation determined that the engine failure was caused by blockage of the carburettor main jet by a piece of silicone rubber used to seal the joint between the carburettor and intake duct. The source did not establish how the foreign object entered the float chamber or fuel line, but it was most likely introduced during maintenance. The blockage prevented the pilot from restarting the engine in flight. Contaminants found in the fuel filter were not considered a cause of the engine failure. The analysis also noted that the pilot selected the landing field based on apparent terrain, choosing a green area believed to be grass over a cereal field. Obstacles in the form of carrot rows and irrigation piping were probably identified only shortly before touchdown, leaving insufficient time to react. The landing configuration—gear extended and flaps closed—was suitable for a grass landing but not for soft, uneven terrain. The absence of extended flaps resulted in a higher touchdown speed. The resulting kinetic energy and uneven surface caused a bounce, followed by nose-down pitching, nose burial in soft ground, and overturning onto the back.