A Robinson R66 broke up in flight just 3.5 seconds after encountering a turbulence‑induced low‑G condition, with the helicopter rapidly rolling to the right and becoming inverted after the main rotor disc became unloaded, an ATSB investigation report details.
The helicopter, with a single pilot on board, had been flying from Cessnock to the New South Wales mid north coast on 26 October 2023 when it encountered the turbulence, likely in the form of rapidly rising air, while passing over the Yacaaba Headland, to the west of Mount Yacaaba, near Hawks Nest.
"The helicopter was flying on autopilot at an indicated airspeed of 115 kt, 45 kt above the manufacturer's maximum recommended speed for flight in significant turbulence," ATSB Director Transport Safety Stuart Macleod noted.
"This speed significantly increased the uncommanded right roll rate and reduced the time available for the pilot to respond by applying a gentle aft cyclic input to re‑load the main rotor disc.
"In addition, the pilot had been eating and had food in their right hand, and so they used their left hand to manipulate the cyclic, reducing their ability to slow the helicopter in a timely manner using coordinated flight control inputs."
Footage from an on‑board video camera was instrumental in detailing the accident sequence, showing that after the helicopter began rolling to the right, the pilot did not apply aft cyclic to reload the main rotor, and the roll continued to develop.
"Instead, the pilot progressively applied increasing left cyclic during the right roll, increasing the risk of an extreme teetering event, where the spindles of the main rotor contact the main rotor shaft, precipitating a break‑up."
The broken‑up helicopter subsequently impacted the waters of Providence Bay, near Hawks Nest, and the pilot was fatally injured.
"The investigation also found that the asymmetrical horizontal stabiliser fitted to Robinson series helicopters, comprising both the piston‑powered R22 and R44 as well as the turbine R66, significantly contributes to uncommanded right roll rates during low‑G conditions, adding to the risk of an in‑flight break‑up."
The stabiliser is an inverted aerofoil that produces downward forces to counter the helicopter's natural tendency to adopt a nose down attitude with increasing air speed. With the asymmetrical design on Robinson helicopters, it extends from the right side of the tail cone, and creates a right rolling moment, which is normally counteracted by a left tilt of the main rotor disc. However, in a low‑G condition where the main rotor disc is unloaded, it cannot counteract the right rolling moment.
"Pleasingly, Robinson Helicopter Company has developed a symmetrical horizontal stabiliser that is being fitted to all new Robinson helicopters, and is available as a modification for all existing Robinson helicopters," Mr Macleod noted.
In addition, Robinson will replace the asymmetric stabiliser with the symmetrical design on all R66s and R44s returned to it for overhaul.
"Further, Robinson Helicopter is in the process of updating several safety notices to provide pilots with improved guidance specific to low‑G, turbulence, and pilot distraction."
Mr Macleod said the ATSB strongly encourages fitment of the symmetrical stabiliser.
"The modification significantly reduces the right roll if a low‑G condition is encountered, allowing pilots more time to recognise and respond to the situation."
Nonetheless, avoiding turbulent conditions where possible, and flying through turbulence at or below the maximum airspeed recommended by the manufacturer, remain critical safety defences for pilots of Robinson helicopters.
"In this case the pilot's response to encountering the low‑G contributed to the development of the in‑flight break‑up, but we would caution all Robinson helicopter pilots that a low‑G condition can result from turbulence directly, and pilots must be ready to respond appropriately," Mr Macleod explained.
"If the main rotor disc is not immediately reloaded, right roll can develop rapidly, particularly when an asymmetrical stabiliser is fitted.
"Therefore it is critical that pilots apply immediate gentle aft cyclic to reload the main rotor, before correcting the right roll."
You can find here the final report: Loss of control and in-flight break-up involving Robinson R66, VH-KFT, near Hawks Nest, New South Wales on 26 October 2023
