What happened
On November 19, 2012, at approximately 13:50 local time, an Aérospatiale AS332L1 helicopter, registered JA9965, was engaged in a cargo lifting operation at the Mt. Shaka loading site in Kitahira, Otsu City. The flight was being conducted by Nakanihon Air Service Co., Ltd., with a trainee pilot performing the lift under the guidance of a captain and an on-board mechanic.
The task involved lifting a box-shaped work shed using sling legs. During the initial lift, several complications arose as the sling legs became entangled with the shed's structure, including a ventilation fan hood and eaves. While the crew attempted to adjust the aircraft's position to clear these obstructions, the ground crew—consisting of a supervisor, safety manager, signalman, and handler—intervened manually to reposition the sling legs.
As the lifting continued, a sling leg became caught on the southeast eaves of the shed. Although the on-board mechanic instructed the pilot to hold the position, the southeast corner of the shed lifted partially off the ground and shifted toward the valley side. At that moment, the handler had rushed to the area to prevent further entanglement. The shifting shed struck the handler, causing him to fall approximately three meters down a slope. The worker suffered a right wrist fracture and a bruised chest.
The investigation
The JTSB investigation focused on the coordination between the flight crew and the ground operators. Investigators examined the safety protocols established by both the aviation company and the ground work company. The inquiry looked into the communication challenges inherent in helicopter sling operations, such as rotor noise and downwash, which can impede clear signaling.
Investigators also reviewed the safety education materials provided to the ground crew. While the aviation company had established procedures stating that workers should not enter the space under or between cargo, the investigation found that the ground operators' actions during the incident deviated from these safety guidelines.
Findings
- The primary cause of the injury was the movement of the shed, which became partially lifted and shifted into the path of the handler.
- A critical discrepance in operational recognition existed between the flight crew and the ground operators regarding how to handle entangled sling legs.
- The ground operators lacked a thorough understanding of the safety instruction to descend and release cargo if an entanglement occurred.
- Effective communication was hindered by the environmental conditions of the helicopter operation, such as noise and downwash.