What happened
On November 28, 2022, a Bell 412EP helicopter, registration JA6977, operated by Shikoku Air Service Co., Ltd., was performing cargo sling operations near the summit of Mt. Ohachi in the Kirishima Mountain Range, Miyazaki Prefecture. The mission involved transporting five pieces of cargo, referred to as "Mokko," from the summit site to a different operation site.
During the first transport, the helicopter attempted to hover over the first cargo load. However, due to wind blowing up from the nearby volcanic crater, the aircraft experienced unstable hovering and difficulty maintaining a precise position. While the hook was being attached, the cargo load swung backward toward the ground personnel. A marshaller, unable to find sufficient space to retreat due to the surrounding terrain, attempted to grab the approaching cargo to avoid being struck. This action resulted in the marshaller being lifted along with the load and subsequently falling onto a mountainside slope, resulting in a pelvic fracture.
The investigation
The Japan Transport Safety Board (JTSB) examined flight data recorder (FDR) records, video footage of the site, and statements from the pilot, onboard operator, and ground crew. The investigation focused on the stability of the helicopter's hover, the visibility of the ground operators from the cockpit, and the safety protocols regarding refuge areas during sling operations. The investigation also looked into the coordination between the various subcontracted companies involved in the ground operations.
Findings
- The helicopter's hovering position was unstable due to turbulence caused by wind currents from the crater, which caused the cargo to swing toward the marshaller.
- The pilot was unable to confirm the marshaller's safety via the cockpit mirror because the worker was positioned in a blind spot.
- The marshaller had limited options for escape because the work area was constrained by steep slopes and rocky terrain.
- The helicopter proceeded with the lifting operation despite the presence of significant turbulence and unstable positioning.
- There were discrepancies in safety awareness and training levels among the different ground operators from various subcontracted companies.