On 20 July 2024, an AS350 BA was involved in an accident near the Paringa River, New Zealand, during a repositioning flight following maintenance. The helicopter lost control during a precautionary landing after an in flight control anomaly developed. Occupants sustained minor injuries; the aircraft was substantially damaged.
Approximately 52 minutes into the flight, the pilot reported a slight jolt and observed that the rotor blades were out of track. Control characteristics subsequently deteriorated, including a significant increase in cyclic force in one direction.
The crew elected to conduct a precautionary landing. At approximately 10–20 ft, the helicopter became uncontrollable, rolled to the left, and impacted terrain.
The investigation determined that a bolt securing the lower attachment of the left main rotor hydraulic servo was not correctly installed during maintenance. The nut was not properly tightened and locking mechanism not installed. The bolt subsequently detached during flight. This resulted in loss of hydraulic assistance in one control axis, increased control loads and asymmetric behaviour and loss of control during the landing phase.
The left and right servos had been swapped during maintenance. The installation of the left servo was not completed correctly. A mandatory duplicate safety inspection was carried out but failed to detect the error. The investigation concluded that the engineers did not adequately verify the work.
Key contributors included task interruption and distraction during maintenance, task switching without adequate controls, delayed or incomplete documentation, fatigue and reduced attention during inspection.
The maintenance provider did not have a sufficiently robust quality assurance process to ensure maintenance tasks were completed and verified correctly.
Despite multiple inspections and post maintenance checks, the error remained undetected.
Following the accident, the maintenance organisation implemented a range of corrective actions, including removal of release to service privileges for involved engineers during investigation, fleet-wide checks of aircraft subject to similar maintenance and delivery of human factors refresher training. Revision of duplicate inspection procedures, with stronger focus on human factors. Introduction of enhanced inspection forms, separating assembly checks, locking checks and functional checks. Improved work pack documentation and sign-off processes, introduction of daily and weekly assurance checks and enhanced post-maintenance inspection checklists. Expanded training on distraction, fatigue, and situational awareness. Introduction of Mental Health First Aid training for staff. Increased focus on error reporting and Just Culture principles. They introduced more robust task card design, Maintenance Line Operations Safety Assessment (M LOSA) programme, improved shift handover processes and measures to create a more distraction free working environment.
Key Safety Lessons
Duplicate Inspection is a Critical Defence and must be independent, methodical and physically verified, not just documented. A second signature alone is insufficient to ensure safety
Human Factors Remain a Primary Risk. Distractions and interruptions can lead to incomplete or incorrect assembly. Fatigue and task pressure may degrade inspection effectiveness. Maintenance systems must be designed to anticipate and trap human error.
Post-Maintenance Flight Risk is Elevated. Aircraft are particularly vulnerable immediately after maintenance.
Control System Integrity is Critical. Any disturbance to primary flight controls requires rigorous verification and enhanced operational caution.
Photo from the official report, credit Amuri Helicopters Ltd