Incident Overview
On the morning of 6 August 2022, a pilot flying a Robinson R22 Beta II helicopter (registration VH-NKV) was en route from Karumba aerodrome, Queensland, to conduct aerial mustering. While cruising at an altitude of about 500–600 ft, the helicopter suddenly began to shake and vibrate. The pilot responded by initiating an autorotation. During the descent, the helicopter flared just above the trees in a heavily wooded area. The aircraft collided with trees and was destroyed. The pilot was not injured, and there was no fire.
Engine Findings
Examination by the Australian Transport Safety Bureau (ATSB) revealed that the engine issues prompting the forced landing were likely caused by carbon deposits that had accumulated on the valve stem of the no. 2 cylinder exhaust valve and within its guide. This buildup reduced the clearance to less than the specified minimum, which likely resulted in the valve binding in the guide and not fully closing. While such deposits would have begun accumulating from the time the cylinder entered service, their progression to the point of degrading engine performance would not normally be detected by the aircraft's existing maintenance regime. The engine had two compression tests within limits shortly before the incident (23 June and 20 July 2022), with no significant degradation noted. However, in the 64 flying hours since the last periodic inspection, the deposits likely progressed to cause the valve to stick.
Operational Context
Cylinder durability issues, predominantly affecting Robinson R22 and R44 helicopters used in mustering operations across northern Australia, have reportedly increased since 2016. Despite considerable investigation by Robinson, Lycoming, industry groups, and the Civil Aviation Safety Authority (CASA), insufficient data has been collected to identify prevention strategies. Only 10% of operators responded to a request for data from the Lycoming Cylinder Durability Investigation Group (LCDIG).
Pilot Actions
During the emergency, the pilot initially raised the collective, which reduced rotor RPM. Recognizing the decreasing engine and rotor RPM, the pilot quickly lowered the collective to maintain rotor RPM and enter autorotation. This deliberate and timely application of the correct procedure almost certainly improved the outcome.
Safety Advisory
In response, the ATSB issued a safety advisory notice (AO-2022-038-SAN-01) strongly encouraging maintainers, operators, and pilots of Robinson R22 and R44 helicopters with Lycoming O-360 and O-540 series engines to complete and return a Lycoming cylinder durability investigation group defect report form whenever engine cylinder issues are identified.