What happened
On the evening of October 24, 2004, a privately-owned Beechcraft C-23, registration JA3683, departed Nagasaki Airport for a ferry flight to Fukuoka Airport. The flight was conducted under Visual Flight Rules (VFR) with a single pilot on board. During the flight, the pilot experienced engine revolutions dropping and noticed fluctuations in fuel pressure. Believing the left fuel tank was nearly empty, the pilot switched the fuel selector to the right tank and subsequently decided to abort the flight to Fukuoka and return to Nagasaki Airport.
While on final approach to runway-A, the pilot attempted to increase power to correct a low approach. At that moment, the engine suddenly stopped. Unable to restart the engine and unable to reach the runway, the pilot performed a ditching in Omura Bay, approximately 4.5km north-northeast of Nagasaki Airport. The aircraft sank in about four meters of water. The pilot, who sustained slight injuries, was rescued from the water by a nearby fishing boat.
The investigation
The investigation focused on the cause of the engine stoppage and the circumstances leading to the ditching. Investigators performed a teardown of the Lycoming O-360-A4J engine, which revealed no mechanical defects, electrical failures, or assembly errors. While seawater-induced corrosion was present due to the immersion, the internal components of the combustion and fuel systems were found to be functional.
Post-ditching analysis of the aircraft's fuel tanks revealed that only a negligible amount of fuel (approximately 550cc of automobile gasoline) remained in both tanks. This contradicted the pilot's earlier belief that there was still significant fuel available in the right tank. Additionally, the investigation noted that the aircraft was being operated using high-octance automobile gasoline rather than the aviation fuel specified in the flight manual, and that uncertified ADF equipment had been reinstalled on the aircraft.