We have done endless test flights over the years with all combinations of SAS ATT FD, on various aircraft at various airspeeds and flight regimes. This exact problem has shown itself on all four of our aircraft so I still think there is an inherent problem with the AHRS / DAFCS and the way it doesn't suppress the oscillations, probably related to the yaw channel as highlighted by TB180 and then the option to change back to pre TB-180 if it improved things. The option to revert to pre TB-180 was after other customers were complaining of cases of Mast Torque fluctuations but Bell gave no details of who they were and what configuration these aircraft were in.