What happened
On October 19, 2011, a B214B-1 helicopter, registered as HL9131, was conducting aerial work to transport construction materials for power-line towers in Gimhae-si, Gyeongsan-nam-do. The aircraft, operated by Hongik Air Service Co., Ltd., was flying under visual flight rules (VFR) and was equipped with a 15-meter synthetic fiber sling strap attached to its belly hook.
While the aircraft was cruising at approximately 70 knots, the pilot executed a simultaneous descent and a deceleration greater than normal. During this maneuver, the empty sling strap became entangled with the tail rotor blades. The crew heard a loud bang followed by significant vibration and a rightward yaw. Despite the pilot's attempt to perform an emergency landing in a nearby valley, the aircraft struck trees and crashed into the ground in a nose-down, left-bank attitude. The impact resulted in two serious injuries to the crew and the total destruction of the aircraft.
The investigation
The ARAIB examined the wreckage, including the main rotor blades, tail rotor assembly, and the 90° gearbox. Investigators found that the synthetic fiber of the sling strap had sustained damage in multiple locations, consistent with contact with the tail rotor. The investigation also reviewed the maintenance logs, which showed no prior defects in the airframe or transmission systems. Furthermore, the investigators analyzed the company's training curriculum and the flight path taken by the pilot prior to the accident.