This paper aims to design a pitch displacement autopilot for business jet aircraft based on root locus modern control system. The control method is used to determine the gains of the controller. To apply the root locus method, a model of the flight system with controllers is developed. The equation of the aircraft motion is determined and the transfer function is derived using the short period approximation. The root locus for the open loop and closed loop systems were obtained. The K values are tested for the damping ratio that keeps the system stable for any change in the gain of the controller. Finally the results of the root locus for each controller gain are analyzed and discussed. The optimum values of controller gain to achieve the desired response and keep the proposed system stable were also determined.

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