Fatal Robinson R66 in-flight break-up following turbulence encounter

1 fatality • Near Hawks Nest, New South Wales

A Robinson R66 helicopter crashed near Hawks Nest, New South Wales, after encountering orographic turbulence that led to a low-G condition and an uncommanded roll.

What happened

On 26 September 2023, a Robinson R66 helicopter, registration VH-KFT, departed Cessnock Airport, New South Wales, flying north along the Williamtown coastal VFR route. As the aircraft crossed the Yacaaba Headland, it encountered significant orographic turbulence. This turbulence caused a rapid climb of approximately 200 feet in 10 seconds, with vertical G-loading exceeding +2 G.

Following this initial upward surge, the aircraft entered a low-G condition. This was exacerbated by the pilot applying a small forward cyclic input. During this period of reduced vertical loading, the aircraft experienced an uncommanded right roll. The aircraft subsequently suffered an in-flight break-up and impacted the waters of Providence Bay, near Hawks Nest. The pilot was fatally injured.

The investigation

Investigators utilized high-fidelity data and cockpit video from a Robinson Helicopter Company camera system to reconstruct the flight path and control inputs. The analysis focused on the interaction between the environmental conditions and the aircraft's aerodynamic response.

Engineers examined the damage to the fuselage and main rotor mast, finding it consistent with mast bumping caused by low-G flight. The investigation also assessed the meteorological conditions, noting that 25–30 kt southerly winds hitting the 41–47° scarp of Mount Yacaaba likely created the turbulent air encountered by the aircraft. Furthermore, the investigation looked at the pilot's control inputs, noting that the right hand was occupied at the time, leading to the cyclic being manipulated with the left hand.

Findings

  • The aircraft crossed the headland at an altitude and position that led to a rapid transition into a low-G state.
  • The aircraft's airspeed exceeded the recommended turbulence airspeed, which increased the rate of the uncommanded right roll and limited the window for corrective action.
  • The asymmetric horizontal stabiliser design in the Robinson R66 contributed to the uncommanded right roll during the low-G phase.
  • The pilot's application of left cyclic in response to the roll increased the risk of an extreme teetering event.

Safety message

  • The Robinson Helicopter Pilot’s Operating Handbook (POH) lacks specific warnings regarding turbulence-induced low-G and rapid right rolls, particularly at high airspeeds.
  • There is a lack of guidance in the POH for appropriate control inputs when encountering turbulence-induced low-G situations.

Probable cause

The aircraft entered a low-G condition due to a combination of orographic turbulence and forward cyclic input, which, at speeds exceeding recommended turbulence limits, triggered an uncommanded right roll and subsequent in-flight break-up.

Frequently asked questions

What happened in the 2023-10-26 Robinson Helicopter Co R66 accident near Near Hawks Nest, New South Wales?

A Robinson R66 helicopter crashed near Hawks Nest, New South Wales, after encountering orographic turbulence that led to a low-G condition and an uncommanded roll.

Were there any fatalities in the 2023-10-26 Robinson Helicopter Co R66 accident?

The accident was fatal, resulting in 1 fatality.

What aircraft was involved and where did it happen?

The accident on 2023-10-26 involved a Robinson Helicopter Co R66, registration VH-KFT, at Near Hawks Nest, New South Wales.

What was the probable cause of the accident?

The aircraft entered a low-G condition due to a combination of orographic turbulence and forward cyclic input, which, at speeds exceeding recommended turbulence limits, triggered an uncommanded right roll and subsequent in-flight break-up.

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