Incident Overview
On October 24, 2022, at approximately 13:08 JST, a Eurocopter AS 350 B3, registration JA02AH, operated by Nakanihon Air Service Co., Ltd., was involved in a serious incident near Ono City, Fukui Prefecture. The helicopter had completed multiple cargo transport operations between a loading site and Yugami Power Plant and was returning to the Kuzuryu Ski Resort Temporary Operation Site when its underslung sling cable contacted overhead transmission lines. The contact caused the sling cable to break, dropping a portion of the hook and cable. The helicopter itself was undamaged, and there were no injuries to personnel.
Flight History
The captain, seated in the right pilot seat, and an onboard mechanic, in the left seat, had conducted a briefing and risk assessment before departure from Nagoya Airport at around 11:00. After landing at Kuzuryu Operation Site at 11:35, a meeting addressed loading site conditions, wind, and the location of transmission lines and bird nests. The helicopter took off at 12:43 with a 21-meter sling cable and performed seven cargo transport cycles between No. 21 loading site and Yugami Power Plant. After the last drop-off around 13:05, the helicopter turned east and began climbing to 3,000 ft at about 40 kt to clear a tower ahead. While climbing at approximately 1,800 ft, the captain spotted a large bird to the left and made a right evasive turn. After avoiding the bird, he saw transmission lines ahead and executed a steep left turn at about 45° bank with deceleration. During the turn, the captain observed the transmission lines from the lower right window. After completing a 360-degree left turn, he saw a hook and cable segment hanging from the lines. Checking the underside mirror confirmed the sling cable was broken. The helicopter continued to Kuzuryu Operation Site, landing at 13:15. The onboard mechanic corroborated the sequence, noting the captain's exclamation and the steep left turn to avoid the lines.
Damage
The sling cable, measuring approximately 21.4 m in total (including a 1.4 m cargo hook section weighing 31.4 kg), showed two black burnt areas 6.4 m apart. The upper burnt area was 7.8 m below the helicopter, and the lower burnt area was 7.2 m above the cargo hook, with the cable fractured below the lower burnt area. Scratch marks were present on the hook at the connection between the 10 m and 5 m sling cables. The control cable had two melting marks 9 m apart. The upper burnt area showed a burn mark consistent with being pressed against a transmission line, while the lower burnt area exhibited circumferential scratches and tearing of the outer skin and inner polyester thread. The transmission lines were damaged: the upper east-side line was made unusable, and the middle east-side line required repair. The lines were out of service from October 24 to December 15, 2022. The high-voltage safety device activated at around 13:08, shutting off power.
Personnel
The captain, aged 36, held a commercial pilot certificate (rotorcraft) issued February 27, 2008, with a type rating for single-turbine (land) and a Class 1 aviation medical certificate. The onboard mechanic's qualifications were not specified.
Location
The incident occurred at an altitude of about 1,900 ft above National Route 158 (coordinates: 35°56'26"N, 136°38'19"E).