The Australian Transport Safety Bureau (ATSB) has warned pilots of Robinson helicopters to slow down in turbulence.
The warning is contained in Safety Advisory Notice AO-2023-051-SAN-001 issued as part of an ongoing investigation into the crash of Robinson R66 VH-KFT near Hawks Nest, NSW, in October last year.
Although the investigation is not complete, the ATSB has said that the circumstances of the crash suggest the aircraft encountered turbulence followed by a low-g condition immediately before the aircraft broke up in flight.
"The ATSB therefore considers it prudent to draw attention to Robinson’s advice regarding flight in turbulent conditions and avoidance/recovery from low‑g flight until such time as the factors that contributed to this accident can be fully established," the SAN states.
"Awareness of conditions likely to produce turbulence, and slowing down prior to encountering turbulence, could increase the time available to recognise and respond to a low-g condition in Robinson Helicopters ...
"The ATSB advises all operators of Robinson helicopters to be aware of the possibility of mechanical turbulence and avoid it whenever possible. If it is not possible to avoid flying through an area where mechanical turbulence is anticipated, reduce airspeed to 60-70 kt in accordance with Robinson Safety Notice 32, prior to encountering turbulence."
According to the ATSB, increased airspeed effects the severity of the helicopter's response, which can result in mast-bumping and in-flight break-up, as outlined in Robinson safety notices SN-11 and SN-32.
"Pilots are reminded to remain vigilant at all times and to continuously assess conditions to identify the possibility for turbulence," the ATSB SAN notes.
"Where any doubt exists, pilots should reduce airspeed prior to entering an area with potential for turbulence to reduce the effects of, and increase the available response time to, an upset condition."
The full safety notice is on the ATSB website.