What happened
On October 15, 2017, at approximately 15:36 JST, a privately owned Beechcraft A3-6, registered JA3842, was conducting a flight approach to Fukui Airport when the engine began to lose power. The aircraft was flying at an altitude of roughly 300 meters, approximately four kilometers northwest of the airfield. During the approach to the traffic pattern, a passenger noticed engine abnormalities, and the pilot attempted to stabilize the engine by adjusting the fuel selector valve from the right tank to the left tank. However, the power loss persisted.
Unable to reach the runway, the pilot performed several maneuvers, including adjustments to the propeller, mixture, and starter switch, while searching for a suitable landing site. The pilot ultimately decided to perform a forced landing and ditched the aircraft in a nearby river. Following the impact, all occupants successfully evacuated the submerged aircraft and swam to the riverbank. The aircraft sustained minor damage, including a deformed nose landing gear door and a detached right main gear.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, fuel loading records, and the aircraft's physical condition. Investigators reviewed data from a portable GPS receiver and a vehicle drive recorder installed in the aircraft, which captured cockpit audio and external imagery. The investigation also analyzed the fuel system, specifically the fuel selector valve and the quantities remaining in the tanks after the aircraft was salvaged from the river.
Findings
- The investigation established that the right fuel tank contained significantly less fuel than the left tank at the time of the incident. While the left tank held approximately 154 liters, the right tank contained only about 1 liter.
- During a refueling stop at Niigata Airport, the pilot did not visually verify the fuel levels during the preflight inspection, relying instead on fuel quantity indicators.
- The pilot's awareness of the fuel gauges decreased during the flight due to the need to monitor heavy cloud cover on the route.
- The engine power loss was caused by the depletion of fuel in the selected right tank, which led to a lack of fuel supply to the engine.
- The loss of power likely persisted even after the pilot switched the fuel selector to the left tank because air may have entered the fuel system, causing a vapor lock, or the fuel-injected engine may have experienced fuel vaporization due to heat.
- The engine failure might have been avoided if the pilot had utilized the auxiliary fuel pump as prescribed in the aircraft's emergency procedures.