What happened
On 22 December 2004, a Hughes 369D helicopter, registration ZK-HHT, was performing a charter flight in the Wanganui River area of South Westland. The mission involved transporting a group of kayakers to the upper reaches of the river, with their equipment—including kayaks and paddles—suspended in a cargo net beneath the aircraft.
As the pilot accelerated to approximately 70 knots and climbed to 500 feet, the aircraft encountered turbulence while rounding a bend in the river. This turbulence caused the sling load to begin oscillating. Before the pilot could reduce speed to stabilize the load, the cargo net swung backward and struck the tail rotor. The impact caused an immediate loss of tail rotor control.
In response to the sudden jolt, the pilot initiated an immediate autorotation. While the pilot managed to steer the aircraft toward a suitable landing area on the riverbed, the subsequent heavy landing caused the tail stinger to strike the ground. This impact severed the tail boom and caused the main rotor blades to strike the rocky terrain. Although the pilot successfully executed a survivable landing, a post-impact fire broke out in the engine bay, ultimately destroying the helicopter. All 4 occupants escaped the wreckage with only minor injuries.
The investigation
TAIC investigators examined the wreckage, the cargo net, and the flight history of the aircraft. The investigation established that the helicopter was airworthy and the pilot was properly licensed. Investigators focused on the configuration of the sling load, noting that the 2-meter strop allowed the net enough freedom to reach the tail rotor during flight oscillations.
Analysis of the pilot's training revealed that while he was experienced in helicopter operations, he had not undergone specific sling load refresher training for several years. The investigation also looked into the weight and balance of the aircraft, confirming the load was within permissible limits, but noted that the load was too light to prevent the aerodynamic streaming effect that contributed to the oscillation.