What happened
On June 2, 2007, at approximately 15:39 JST, a Bell 412 helicopter, registration JA9991, crashed into a mountain slope in the Ichinosawa ravine, roughly 1.3km north of a temporary helipad in Nakatsugawa City, Gifu Prefecture. The aircraft, operated by Toho Air Service Co., Ltd., was performing aerial reforestation work, using a slung bucket to spread a mixture of seeds, fertilizer, and water onto landslide-damaged slopes.
On the day of the accident, the pilot had completed 68 circuits of aerial spreading. During the final leg of the mission, while returning to the helipad, the aircraft struck trees on a steep slope. The impact destroyed the fuselage, skids, and rotor components. The pilot, who was the sole occupant of the aircraft, was found fatally injured near the wreckage.
The investigation
Investigators from the Aircraft and Railway Accidents Investigation Commission (ARAIC) examined the wreckage and the accident site, which featured a 45-degree slope covered in dense vegetation. The investigation focused on the aircraft's fuel management and the sequence of events leading to the impact.
Evidence from the wreckage showed that the aircraft's main rotor blades had struck trees, causing the rotor speed to drop and the aircraft to tumble down the slope. The investigation also reviewed communications between the pilot and ground personnel. While the weather at the helipad was clear with calm winds, the mountain tops were obscured by fog. Personnel at the helipad reported that the pilot had communicated that the current circuit would be the last of the day, but no further radio contact was established after the aircraft departed for its final return.
Findings
- The primary cause of the accident was in-flight fuel starvation.
- The pilot's fuel management strategy prioritized operational efficiency, likely intending to complete the mission before the 'FUEL LOW' caution light illuminated, rather than using the light as a trigger for immediate refueling.
- The pilot's psychological desire to conclude the day's work contributed to the decision to continue flying with low fuel reserves.
- A lack of shared information regarding fuel levels meant that ground mechanics and other personnel were not actively involved in monitoring the aircraft's fuel status, leaving the sole pilot responsible for all fuel-related decisions.
- There was a delay in notifying search and rescue organizations, as the company initially focused on internal information gathering and search efforts.