What happened
On September 29, 2023, at approximately 10:25 JST, a Bell 412EP helicopter, registration JA6977, operated by Shikoku Air Service Co., Ltd., was performing cargo transport duties at the summit of Mt. Daisen in Tottori Prefecture, Japan. The mission involved transporting renovation materials for a wooden path using underslung external cargo.
During the sixth transport of the day, the helicopter approached the unloading site to deposit a cargo net containing approximately 832 kg of materials. As the helicopter descended, the downward airflow from the main rotor caused the cargo net to swing. While the net appeared stable during the final descent, the end of the net that touched the ground first acted as a pivot point, causing the remaining portion of the net to swing toward a nearby wooden path.
A ground operator, acting as a signal person, moved toward the wooden path to prepare for potential assistance work. During this movement, the signal person became momentarily distracted by the actions of an assistant ground operator. In this moment of distraction, the swinging cargo net struck the signal person's left leg, resulting in a serious injury (a fractured fibula).
The investigation
The Japan Transport Safety Board (JTSB) investigated the incident, examining the flight history, the physical characteristics of the unloading site, and the equipment used. The investigation focused on the movement of the cargo net, the positioning of the ground personnel, and the safety procedures in place at the time of the accident.
Investigators noted that the unloading site was narrow and featured a slight downward slope toward the wooden path. They also examined the lack of specific assistance ropes attached to the cargo net, which necessitated the ground operator being in close proximity to the load.
Findings
- The signal person was positioned within the potential swing radius of the cargo net because the cargo net lacked an assistance rope, requiring the operator to touch the load directly to adjust its position.
- The swing of the cargo net was likely caused by the pivot effect of the net hitting the ground first, compounded by the downward wind from the helicopter's rotor and the sloping terrain.
- The signal person's attention was diverted by the movement of the assistant ground operator, leading to a loss of visual contact with the cargo net.
- The signal person failed to move to a safe distance after providing instructions, as required by established safety procedures.
Safety action
Following the accident, Shikoku Air Service Co., Ltd. implemented several safety measures:
- Revised cargo transport procedures to mandate that ground operators must not touch suspended cargo and must maintain a safe distance.
- Established a requirement to use support ropes for any cargo requiring positional adjustment to ensure workers can assist from a safe distance.
- Conducted safety re-education for all pilots, mechanics, and ground personnel involved in cargo operations.