A robust autopilot for attitude control of the flexible aircraft under parametric uncertainty is designed. The high gain controller with forced sliding motions is used to secure adaptability in the wide region of the aircraft model parameters. The shunting method is applied to ensure the closed-loop system stability in the face of the lack of the aircraft state information. The sequential reference model is used to assign the desired closed-loop system performance. An example illustrating a typical design procedure for aircraft attitude control in the horizontal plane for different flight conditions is given. The system robustness with respect to uncertain plant parameters is studied. The simulation results demonstrate efficiency and high robustness of the suggested control method.