The paper discusses feedback control strategies for the reduction of helicopter vibration using a trailing edge flap located at the outer part of the rotor blades. The problem of reducing rotor-induced vibration is considered as a disturbance rejection control problem where robust servomechanism control is applied in combination with optimal constant output feedback. This control scheme is examined in the view of limitations in the transient performance by investigating the zeros of the multivariable system. Local control strategies in the rotating system are developed for active damping enhancement. Simulations are presented based on a BO105 helicopter.