What happened
On March 6, 2015, an Aerospatiale AS332L1, registered JA6741, was performing external load transportation tasks near Kii-Nagashima, Japan. The aircraft, operated by Shin Nihon Helicopter Co., Ltd., had been transporting sandbags and steel frames using a sling device between a forward base and a loading site in the Yamato-d'ani valley.
After completing the unloading of steel frames at the forward base, the aircraft attempted to climb from a hover to depart the site. During this maneuver, the helicopter struck overhead power transmission lines. The impact caused the tail boom to break away and the main rotor blades to separate from the aircraft. The helicopter subsequently crashed into a steep, forested mountainside, where a fire broke out. The collision also severed two power lines, resulting in a temporary blackout for approximately 18,700 households in the region.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation involving on-site inspections of the wreckage and the power lines, as well as interviews with ground personnel. Investigators examined the flight history, noting that the crew had performed a preliminary survey flight earlier that morning to identify obstacles. The investigation also reviewed the company's operational standards, maintenance records, and the specific flight conditions at the time of the accident, which included good visibility and calm winds.
Findings
- The primary cause of the accident was that the Helicopter failed to maintain a sufficient distance from the overhead power transmission lines during its departure from the hover.
- It is probable that the pilot did not visually identify the lines in time or misjudged the distance to the linear obstacles.
- Contributing factors may have included the pilot's focus on cockpit instruments, potential sunlight glare, or the difficulty of perceiving the distance to the lines due to their steep angle.
- The investigation also noted that while the pilot had identified the lines during a prior survey, the lack of specific callout procedures for departure maneuvers and the absence of obstacle markings on the lines may have contributed to the oversight.