What happened
During a local flight following maintenance procedures, an aircraft departed from Yonago-Miho Air Base. The flight was being operated by a crew consisting of four pilots and four technicians. After the aircraft had completed several circuits, it reached its cruising altitude.
While maintaining this altitude, the aircraft transitioned into an uncontrolled descent. The descent continued until the aircraft impacted the sea in the vicinity of Shimano. There were no survivors of the impact; the crash resulted in eight fatalities.
Findings
Following the crash, investigations focused on the period when the aircraft lost stability during its cruise phase. The primary factor identified in the sequence of events was the uncontrolled descent that occurred after the initial flight circuits were completed.