What happened
On 2 January 2022, a Robinson R22 Beta II helicopter, registration ZK-HEQ, was performing passenger transfers in the Kahurangi National Park. After dropping two passengers at a remote location for a hunting trip, the pilot began the return flight to Karamea.
Shortly after departing the drop-off point, the pilot noticed a severe vibration and an unusual noise coming from the rear of the aircraft. Despite the disturbance, the pilot elected to continue the flight to Karamea. Witnesses on the ground observed the helicopter flying at an unusual altitude and path, noting that the engine sound was distinctly different from normal.
As the helicopter approached the landing site near the Karamea River, the aircraft began pitching abruptly and rotating to the right. During this sequence, parts of the empennary assembly detached and fell from the aircraft. The helicopter struck the ground almost vertically, resulting in the destruction of the aircraft and one fatality (the pilot), who sustained serious injuries.
The investigation
The Transport Accident Investigation Commission (TAIC) examined the wreckage and flight data to determine the cause of the structural failure. Investigators analyzed the tail rotor drive shaft, which showed evidence of permanent deformation.
Technical examination of the site revealed that the tail rotor drive shaft had twisted and failed due to overload. The investigation also reviewed maintenance records, noting that while the aircraft had been maintained according to schedule, the engine had slightly exceeded its time-between-overhaul limit. The investigation also looked into the possibility of a rotor overspeed, a condition where the drivetrain exceeds the manufacturer's permitted RPM limits.
Findings
- The investigation determined that the helicopter most likely experienced a rotor overspeed during the return flight.
- This overspeed caused the tail rotor drive shaft to deform.
- During the landing attempt, the application of increased power and collective caused the already deformed drive shaft to contact the internal structure of the tailcone and the tail rotor control tube.
- This contact led to a total loss of tail rotor control, causing the pilot to lose directional control of the aircraft.
- The overspeed was likely caused by the aircraft being flown outside the approved rotor speed limitations.
Safety action
- Pilots must maintain strict vigilance to ensure that rotor RPM remains within the operational limits specified in the Pilot’s Operating Handbook.
- Aircraft operators must ensure all maintenance programs and New Zealand Civil Aviation Rules are strictly followed to maintain continued airworthiness.