What happened
On the morning of 15 March 2002, a Schweizer 269C helicopter, registration ZK-HIC, was performing agricultural spraying operations near Karaka Downs, South Auckland. During a pull-up maneuver at the end of a low-level spraying run, the aircraft suddenly lost tail rotor authority and entered a rapid right-hand spin.
The pilot attempted to arrest the rotation by applying full left pedal, reducing throttle, and lowering the collective. While these actions slowed the spin, the pilot was unable to regain directional control. To prevent a more violent impact, the pilot executed an emergency landing, causing the aircraft to strike swampy ground and come to rest on its side. The pilot, who was the sole occupant, escaped the crash without injury.
The investigation
Investigators examined the tail rotor drive train and the maintenance history of the aircraft. The investigation focused on the mechanical state of the driveshaft and the gearbox following a recent GPS installation. During this modification, the tail rotor gearbox and driveshaft had been removed and reinstalled.
Technical analysis revealed that a defective bumper plug on the tail rotor driveshaft had failed. This component is designed to limit the fore and aft movement of the shaft. The investigation also looked into maintenance records, noting that while an O-ring replacement had been performed during the GPS installation, there was no clear logbook entry or evidence of a required duplicate inspection for the disturbed yaw control system.