Although the helicopter manufacturer’s instructions for continuation in service for the clutch shaft forward yoke specified that the condition of the yoke was to be inspected to verify that no cracks, corrosion, or fretting was present, it did not provide specific instructions for the method to be employed. The visual inspection that was employed increased the risk that a crack in that area may not be detected.
The ATSB is satisfied that the amendments to the aircraft maintenance manual will result in yokes being removed from service before cracks on the forward face progress to failure. As such, the ATSB considered that the safety issue had been adequately addressed.
On advice from the FAA, the helicopter manufacturer conducted a risk assessment that resulted in no need for immediate airworthiness action but did recommend long term airworthiness action.
The helicopter manufacturer advised the ATSB that as a result, they would be introducing new requirements for the clutch shaft forward yoke at the 2,200/2,400‑hour inspection. This included replacement of yokes with earlier revisions (A through G), or the option of replacement or a more detailed inspection, including a magnetic particle inspection, for later revisions. This update was included in the R44 maintenance manual in August 2022.
The helicopter manufacturer also advised that as a result of the contributing safety issue, they initiated additional safety action by revising the paint colour of the yokes at the forward flex coupling from dark grey to white. The colour change was to enhance the visibility of fretting dust during inspections in the event of loose hardware.
