What happened
On March 24, 2003, a Gulfstream Commander 695, registration JA8604, departed Chofu Aerodrome for a scheduled company test flight. The mission, conducted by Asia Air Survey Company Limited, was intended to verify the functionality of the cabin pressurization system and VOR/DME receivers prior to an airworthiness certification inspection.
During the flight, the aircraft climbed to altitudes exceeding 23,000 feet. At approximately 10:50 JST, the aircraft began a rapid descent. Radar records indicate that after maintaining a steady climb, the aircraft's altitude dropped precipitously from 21,100 feet to 3,200 feet in less than two minutes. The aircraft subsequently crashed into a wooded area in Ogawa, Naka County, Ibarable Prefecture. The impact resulted in two fatalities, claiming the lives of both the captain and the mechanic.
The investigation
The investigation examined the aircraft's mechanical condition, the flight's trajectory, and the physiological state of the crew. Investigators analyzed the wreckage, including the engines and propellers, and performed a detailed inspection of the lubrication system.
Key areas of focus included the engine oil filler port, the cabin pressurization system, and the oxygen supply. The investigation also reviewed the aircraft's flight history, the pilot's recent experience, and the meteorological conditions at the time of the accident. Furthermore, the team evaluated the possibility of crew incapacitation due to hypoxia, considering the altitude reached and the time elapsed during the descent.