What happened
On September 23, 2013, a privately owned Fuji Heavy Industries FA-200-160, registration JA3492, was conducting a sightseeing flight near Yachiyo City, Chiba Prefecture, Japan. The aircraft had departed from Otone Landing Field with a pilot, a co-pilot, and two passengers. During the flight, while cruising at 1,500 feet, the engine began to malfunction. The pilot attempted to rectify the issue by utilizing the fuel carburetor heater, the electric fuel pump, and adjusting the throttle, but these efforts were unsuccessful. As the engine stopped, the pilot maneuvered the aircraft away from residential areas toward a rural area, eventually performing an emergency landing in a harvested rice field. The impact caused the landing gear to break off, with one wheel striking the vertical stabilizer, resulting in substantial damage to the airframe and one minor injury.
The investigation
The investigation focused on the fuel system and the circumstances leading to the engine failure. Investigators examined the fuel levels recorded during the day's various flights and analyzed the aircraft's fuel consumption patterns. The inspection of the fuel system revealed that while the right fuel tank was nearly empty, the left fuel tank remained at its pre-flight level. Post-accident analysis of the fuel system components identified that the check valve located between the left fuel tank and the sump tank had been improperly mounted, with the hinge positions not aligned with the manufacturer's manual. Furthermore, the investigation found that the aircraft had a known tendency for asymmetrical fuel consumption, which the crew had observed during previous flights that day.
Findings
- The engine stopped because the fuel supply was interrupted, leaving no fuel in the carburetor.
- The interruption occurred because the left check valve became stuck in the closed position, preventing fuel from the left tank from reaching the sump tank.
- The crew misidentified the significant fuel imbalance as a routine or temporary phenomenon rather than a sign of a mechanical failure.
- The fuel imbalance had reached levels that, according to manufacturer service notices, should have triggered a mandatory adjustment or flight cancellation.
- The presence of mud and foreign substances was found inside the sump tank during cleaning.