The Robinson Helicopter pilot’s operating handbook sections for operation in high winds or turbulence did not warn of the potential for turbulence-induced low‑G, and rapid right roll, particularly at high airspeed or provide guidance for appropriate control inputs in response to a turbulence-induced low‑G situation. This increased the risk of pilots encountering low‑G independent of control inputs, and an in‑flight break‑up.
Response by Robinson Helicopter Company
Robinson Helicopter Company (RHC) advised that it was currently reviewing and revising the pilot’s operating handbook, including the applicable safety notices, to improve guidance on the low-G condition, flight in turbulent conditions, and pilot distraction.
ATSB comment
The ATSB welcomes the documentation review being undertaken by RHC and will continue to monitor the safety issue until the proposed safety action is complete.
Robinson Helicopter Company (RHC) advised that it was currently reviewing and revising the pilot’s operating handbooks, including the applicable safety notices, to improve guidance on the low-G condition, flight in turbulent conditions, and pilot distraction.
Robinson Helicopter Company updated the wording in Safety Notices SN-11 to introduce the contribution of the asymmetric stabiliser and clarify the role airspeed plays with relation to the low-G right roll, as well as introduce the symmetric stabiliser and the expected aircraft reaction to low-G. The SN-11 update also acknowledges turbulence as a possible contributing factor to low-G.
The updates also introduce the low-G condition and response with respect to turbulence in Safety Notice SN-32, as well as clarifying the defined turbulence conditions where reduced airspeed is recommended.
The updates to Safety Notice SN-11 and SN-32 go some way to addressing the concerns raised in Safety Issue AO-2023-051-SI-01, in that they acknowledge that turbulence as a possible contributing factor to the low-G condition, clarify the role airspeed plays in the development of a low-G right roll, and describe the mechanism that produces the uncommanded right roll.
However, both Safety Notices effectively state that the low-G condition can only result as a result of pilot mishandling, and does not acknowledge the potential risk of a turbulence induced low-G condition without pilot control input.
The ATSB believe that informing pilots of the potential dangers of turbulence, specifically the risk of turbulence induced low-G, is critical for safety. By avoiding clear communication of this point, the opportunity to improve safety has not been fully taken advantage of.
For this reason, a standalone Safety Recommendation AO-2023-051-SR-01 has been raised specifically to this point,
The Australian Transport Safety Bureau recommends that Robinson Helicopter Company warns pilots of the potential for turbulence to induce a low-G condition, without any requisite pilot control inputs.
Due to the potentially small window of time available for pilots to recognise and respond to the condition, the ATSB considers that the emphasis that was initially proposed by the Robinson Helicopter Company is necessary to sufficiently alert pilots to the hazard.
