What happened
On November 22, 2015, a privately owned Robinson R22 Beta, registration JA7963, departed Tokyo Heliport for a familiarization flight to the Komoro Temporary Helipad in Nagano Prefecture. The flight was conducted under Visual Flight Rules (VFR).
During the transit, the weather conditions deteriorated. As the rotorcraft approached the area near Matsuida Town in Gunma Prefecture, low cloud cover began to obscure the terrain. GPS records and eyewitness accounts indicate that the aircraft was maneuvering near the Joshin-etsu Expressway, attempting to navigate through changing visibility. At approximately 10:56 JST, the rotorcraft struck the artificial slope face of a mountain. The impact destroyed the aircraft, and both the pilot and the passenger sustained fatal injuries.
The investigation
The Japan Transport Safety Board (JTSB) examined several sources of evidence, including GPS data from a portable receiver, communication logs from the Tokyo Flight Service, and digital images from a camera carried by the passenger. Investigators also interviewed eyewitnesses who observed the aircraft flying at a low altitude and noted a change in engine sound before the impact.
Technical analysis focused on the aircraft's flight path and the meteorological conditions at the time. Investigators reviewed the flight route, noting that while the pilot had previously used a safer route via the Usui Mountain Pass to avoid high terrain, the route taken during this flight crossed directly through the Kanto Mountains. The investigation also analyzed the possibility of the aircraft entering a Vortex Ring State (VRS) due to high rates of descent and low airspeed during the period of deteriorating visibility.
Findings
- The pilot elected to continue the flight despite worsening weather conditions, likely in an attempt to locate a viable route to the destination.
- To maintain visual contact with the ground under conditions where Visual Meteorological Conditions (VMC) could no longer be sustained, the aircraft was forced to fly at a dangerously low altitude.
- The aircraft's path took it directly into the mountain slope near the expressway.
- The pilot continued the flight despite deteriorating weather, which led to the necessity of flying at low altitudes to maintain visibility, ultimately resulting in the collision.