What happened
While performing aerial medical work near Katoomba, New South and Wales, a Leonardo Helicopters AW139, registration VH-TJH, was positioned approximately 85 ft AGL to winch a paramedic to an injured bushwalker. As the crew began the lowering process, the aircraft drifted toward a nearby cliff face. The pilot responded with a significant nose-up pitch of approximately 51° to avoid the terrain, a maneuver that resulted in an engine over-torque. Following the incident, the paramedic was successfully retrieved, and the aircraft returned to Bankstown without further incident.
The investigation
The investigation focused on the operational and environmental conditions during the Night Vision Imaging System (NVIS) operation. While the aircraft was equipped with two white lights as required by regulations, these lights were found to be insufficient for maintaining visual references. The crew had positioned the aircraft facing the cliff to maximize available light, but the area remained poorly illuminated.
Engineers found no mechanical defects or pilot physiological issues. However, the investigation noted that the crew's in-flight risk assessment failed to fully address the risks of the degraded illumination and the lack of a visible horizon caused by the aircraft being in the moon's shadow. Furthermore, the investigation highlighted that the pilot's workload was significantly increased due to the inadequate lighting, which contributed to the disorientation.
Findings
- The external white lighting on the aircraft was inadequate to illuminate the terrain effectively at the required altitude.
- The pilot experienced an unusually high workload due to reduced visual cues, leading to a misidentification of hover references and subsequent disorientation.
- Regulatory standards did not provide specific requirements for the minimum intensity of aircraft lighting for NVIS operations.
- The crew's in-flight risk assessment did not sufficiently account for the hazards of the specific winch site, such as the lack of a horizon.
- There was insufficient recent experience (recency) for the crew regarding complex NVIS winching operations.