Abstract: When actuators are saturated, the additional time delay would occur, which drastically reduces the stability margins of the closed loop and increases t he r isk of pilot-induced oscillations (PIO) . T he software rate limiters areusually used in flight control laws to prevent the actuator saturation. This paper describes the open loop and closedloop proper ties of thr ee kinds of software r ate limiters. A method is proposed to prevent the PIO due to actuator saturation for the example air craft. T he six degrees of freedom (SDOF) flight simulation results demonstrate that thismethod improves significantly the aircr aft closed loop stability and flying qualities, and r educes the PIO tendency.

Key words: PIO, software rate limiter, flight control laws