What happened
On the morning of September 26, 2010, an Aerospatiale AS332L, registered JA9635, was performing a sling load operation to transport construction stones for mountain trail maintenance. Operated by Aero Asahi Corporation, the helicopter was shuttling between a temporary helipad at Yakusugi Land and various unloading sites near the Yodogawa Mountain Hut.
During the sixth cargo lift of the day, the aircraft was flying through a mountain valley with approximately 2,700 kilograms of stones suspended from its external cargo hook. As the pilot attempted a left turn to maneuver through the valley, the underslung cargo struck ground objects. This caused the helicopter to strike a mountain slope near the Kigensugi cedar tree. The impact was followed by a post-crash fire that consumed the wreckage. Both the pilot and the loadmaster sustained fatal injuries.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, aircraft condition, and environmental factors. Investigators reviewed the maintenance records, which showed no anomalies during the preflight inspection. The investigation also analyzed the aircraft's weight and balance, noting that the total operating weight, including the cargo, was approximately 8,003 kilograms, well within the allowable limits.
Witness accounts from ground mechanics and construction workers provided a timeline of the deteriorating weather conditions. The investigation also looked into the communication challenges faced by the crew, noting that the mountainous terrain limited VHF and mobile phone reception, which delayed the initial emergency response.