What happened
On August 10, 2018, at approximately 10:01 JST, a Bell 412EP helicopter, registered JA200G, crashed into a mountain slope near Mt. Yokote in Nakanojo Town, Gunma Prefecture. The aircraft, operated by the Gunma Prefectural Disaster Prevention Aviation Unit, had departed from the Gunma heliport in Maebashi City. The mission was intended to scout and identify hazardous locations along mountain trails to prepare for upcoming rescue operations.
During the flight, the aircraft encountered cloudy airspace, which significantly reduced visibility. The impact with the terrain resulted in the deaths of all nine persons on board, including the captain, a mechanic, a chief air rescuer, an air rescuer, and five firefighters. While the helicopter was destroyed upon impact, no fire broke out at the crash site.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, meteorological data, and the aircraft's technical systems. Investigators analyzed GPS records, video camera footage from the area, and the flight control computer's error logs. The investigation also reviewed the pilot's decision-making process regarding weather conditions and the maintenance of Visual Meteorological Conditions (VMC). Furthermore, the JTSB evaluated the effectiveness of the crew's ability to manage the aircraft's attitude when visual contact with the ground was lost.
Findings
- The pilot experienced spatial disorientation after the aircraft entered cloudy terrain.
- The loss of continuous visual contact with the ground surface made it impossible for the pilot to maintain the necessary aircraft attitude.
- The crew failed to promptly transition to instrument flight or exit the deteriorating weather.
- A critical factor was the delayed decision to return to base, which allowed the flight to continue into conditions where maintaining VMC was no longer possible.