What happened
On the evening of January 3, 2011, a privately owned Piper PA-4SS0P, registration JA701M, departed Kumamoto Airport for Kitakyushu Airport. The flight was conducted under Visual Flight Rules (VFR). Shortly after takeoff, the aircraft began a climb, but the pilot reported a target altitude of 6,500 feet while the aircraft was actually struggling to maintain a steady ascent.
During the climb, the aircraft entered cloud cover. The radar signal from the aircraft vanished at approximately 17:14 JST. The wreckage was discovered the following day on the south-southeast slope of Mt. Y0ago, roughly 14 km northeast of Kumamoto Airport. The impact with the terrain destroyed the aircraft, and both the pilot and the passenger sustained fatal injuries.
The investigation
The Japan Transport Safety Board (JTSB) examined the aircraft's flight history, radar track records, and meteorological data. Investigators analyzed the engine instruments and navigation device data to reconstruct the flight path. The investigation also included interviews with air traffic controllers, eyewitnesses, and a passenger who had been on the aircraft earlier that day.
Weather observations at the time indicated low visibility, rain, and snow in the area, with cloud bases as low as 1,500 feet. The investigation focused on why the aircraft, operating under VFR, entered IMC (Instrument Meteorological Conditions) and why the pilot failed to avoid the mountain terrain.