EASA 2023-0168

Require repetitive inspection for corrosion on the tail rotor transmission's inclined and horizontal drive shafts and any necessary corrective actions. Prompted by several reported occurrences of finding corrosion on contact surfaces of the tail rotor's inclined and horizontal drive shaft flanges. Although more detailed non-destructive testing did not indicate any cracks or corrosion of the flange jo-bolt holes, indications were found for pitting corrosion on the mating faces of several flanges. Further investigation of exposed flange surfaces revealed various regions of intergranular failure beneath the surface of found corrosion pits. If not detected and corrected, this condition could lead to failure of the tail rotor drive.