EASA 2019-0172

Requires a one-time inspection of the lock washer position of the main rotor hub phonic wheel and, depending on findings, replacement with a serviceable part. Prompted by reports of fluctuation of main rotor rotation speed. A subsequent investigation identified incorrect position of main rotor hub phonic wheel due to incorrect installation of the press screws of the nut of the main rotor mast during maintenance visits of MRH assemblies. The investigation also determined that incorrect installation can be identified by inspecting the phonic wheel lock washer position.