Accident Summary
On Thursday, June 15, 2023, at about 13:30 Japan Standard Time, a ground operator (Ground Operator A) was seriously injured during a cargo sling operation in the mountains of Nantan City, Kyoto Prefecture. The helicopter involved was an Aerospatiale AS332L1 (registration JA9678) operated by Aero Asahi Corporation. The ground operator sustained extensive skin exfoliation requiring hospitalization.
Flight Details
The helicopter was performing external cargo sling operations for power line replacement work. It took off from an operation site in Hatago District, Hiyoshi Town, Nantan City, at about 13:15. The crew consisted of a captain (age 42) in the right cockpit seat and an onboard mechanic (age 28) in the guide's seat in the left aft cabin. The helicopter was equipped with sling wire ropes approximately 20 meters in length and hooks. The loading site contained three cargo nets (Cargo net 1, 2, and 3) on a slope. Cargo net 1 weighed about 500 kg, Cargo net 2 about 1,000 kg, and Cargo net 3 about 600 kg.
At about 13:24, the captain positioned the helicopter above the loading site at about 40 m AGL, descended to about 21 m AGL, and hovered. The onboard mechanic guided the helicopter so that the hooks would be positioned between Cargo net 2 and Cargo net 3. Two ground operators were present: Ground Operator A (age 52, about 30 years of experience) and Ground Operator B (age 55, about 30 years of experience). After hooking the sling wire ropes onto the cargo hook, Ground Operator A moved to a position to reach the hooks. Ground Operator B sent a hand signal 'Climb' to the onboard mechanic.
As the helicopter climbed, the sling wire ropes of Cargo net 1 became taut, causing Cargo net 1 to drag on the slope. Ground Operator A noticed a rootstock caught in the stitch of Cargo net 1 and performed support work by pushing the left side of Cargo net 1 towards the mountain side. The onboard mechanic observed Ground Operator A touching Cargo net 1 but, seeing no signal from Ground Operator B, judged there was no danger and continued guiding the helicopter to climb slowly. At about 13:30, the onboard mechanic witnessed Cargo net 2 swing counter-clockwise and come into contact with Ground Operator A's left arm after its sling wire ropes became taut.
Injuries and Response
Ground Operator A's arm was caught between Cargo net 1 and Cargo net 2. He managed to pull his arm out and moved to the mountain side while holding his left arm. The onboard mechanic reported the situation to the captain, who communicated via radio to company staff at the unloading site that a ground operator might be injured. The captain then headed to the unloading site, unloaded the cargo nets, and returned to the operation site, landing at about 13:39. Ground Operator A descended the mountain with another ground operator and was transported to a hospital in Kyoto City, where he was diagnosed with extensive skin exfoliation requiring hospitalization.
Analysis
The Japan Transport Safety Board (JTSB) concluded that it is certain that Ground Operator A was injured because Cargo net 2 swung around and came into contact with his left arm as the helicopter lifted the three cargo nets. Cargo net 2 was dragged to the mountain side and most likely swung around the point where it touched the ground as a fulcrum. The JTSB found that Ground Operator A was performing support work without moving to a safety position, despite the helicopter having started to lift the cargo nets. Ground Operator B did not notice Ground Operator A approaching the cargo net. The JTSB also concluded that the onboard mechanic highly probably continued providing guidance instructions for the helicopter to climb while recognizing that Ground Operator A was not moving to a safe position, because there was no signal from Ground Operator B. The JTSB noted that the company's operations manual requires ground operators to move to a safety position after hooking cargo; if support work is unavoidable, it must be done in a short time with great care. The company provided education and training on safety related to ground work.
Probable Cause
Not explicitly stated in the investigation report.