The pilot of a Bell LongRanger experienced a loss of tail rotor effectiveness while conducting weed surveying over the Snowy River, resulting in the helicopter striking a large boulder in the river during the subsequent emergency landing, an ATSB investigation report details.
The helicopter, which was operated by Heli Surveys, had been tasked to conduct a low-level weed survey task for the NSW National Parks and Wildlife Service (NPWS). On board the flight, which had departed Jindabyne on the morning of 11 March 2022, were the pilot and four NPWS officers.
To facilitate the survey, the helicopter was flying at a low height over the Snow River's southern riverbank, with the nose of the helicopter yawed to the right (i.e. sideways) at a speed of about 30 kt.
After the pilot made a light control input on the left anti-torque pedal, in an attempt to straighten the nose and improve their forward vision, the helicopter experienced an uncommanded yaw to the right. As the yaw rate accelerated the pilot decided that their only option was to reduce the throttle to idle, which stopped the yawing motion. The pilot was then committed to an emergency landing in the river, during which it struck a large, unsighted boulder.
The impact with the boulder partially separated the helicopter's forward cockpit section from the cabin area and resulted in the tailboom partially fracturing. Three of the helicopter's occupants sustained serious injuries and 2 received minor injuries.
"The investigation found that the combination of low-level, slow speed flight while yawed to the right by about 45°, and operating at a high gross weight and density altitude, were conducive to a loss of tail rotor effectiveness," ATSB Director Transport Safety Kerri Hughes said.
"As such, it was likely that a loss of tail rotor effectiveness occurred at an insufficient height to recover and avoid a collision with terrain."
Ms Hughes explained that loss of tail rotor effectiveness (LTE) can occur when the airflow through a helicopter's tail rotor is changed, such as by altering the angle or speed at which turbulent air from the main rotor washes into the rotating blades of the tail rotor disc.
"The investigation identified that the operator's risk assessment for low-level operations did not contain the hazard and control measures to avoid the likelihood of loss of tail rotor effectiveness," she said.
"Further, there was no requirement for its pilots to conduct pre-flight risk reviews to ensure that operations could be conducted without unacceptable safety risk."
In addition, the investigation found that one of the NPWS officers on board was not required for the survey task, which unnecessarily exposed them to the risks associated with low-level flight.
"While the client's operating procedures referred to only permitting 'essential personnel' on flights, they did not provide a definition or specify the roles and responsibilities of these personnel."
Since the accident, Heli Surveys has conducted a review of its risk management processes and made changes to its operational conduct, while the NPWS has revised its aviation safety policy and developed an aviation safety management system to enhance safety and manage risk across its aviation activities and operations.
"Survey flights, particularly when performed in alpine environments, are generally conducted at low level and slow speeds," Ms Hughes concluded.
"This creates a high-risk operating environment that requires effective risk management."
The ATSB investigation report highlights that risk management should include an overarching pre‑operational risk assessment to identify the hazards and risks common to that type of operation.
"This assessment can then be used to inform the management of risk for specific taskings including a pilot's pre-flight risk review, to ensure the operation can be conducted safely."
You can find here the final report: Collision with terrain involving Bell 206L-1, VH-BHF, 20 km north-west of Jindabyne, New South Wales, on 11 March 2022
