What happened
On October 23, 2008, at approximately 12:15 JST, an Aerospatiale SA315B Alouette III, registration JA6117, was performing a cargo transport mission at the Tazawako-Obonai temporary helibase in Akita Prefecture. The aircraft, operated by Toho Air Service Co., Ltd., was approaching the helipad to deliver materials for a broadcasting antenna construction project.
As the pilot transitioned to a hover and began the final descent to the landing pad, the downwash from the main rotor interacted with blue polyester tarpaulin sheets located near a fuel storage area. Although the sheets had been folded and weighted with timber, the force of the air lifted one of the sheets into the air. The sheet was subsequently sucked into the rotating main rotor disc.
Upon touchdown, the aircraft experienced severe vibrations and a sudden yaw. The impact of the debris and the resulting aerodynamic imbalance caused significant structural damage, including a bent tailboom, a broken left shock strut, and damage to one of the main rotor blades. There were no injuries to the pilot, mechanic, or passenger on board.