In the paper a flight control system for a piloted aircraft on the pitch angle is considered, taking into account the rate saturation of the aircraft controlling surface. To prevent occurrence of the non-linear pilot-involved oscillations (PIO), a nonlinear correcting device is introduced into the control loop. On the basis of the pilot's adaptation to control tasks variations, his/her mathematical model parameters are optimized and the choice of the nonlinear correcting device parameters is proposed. The sensitivity functions of the non-linear system are calculated for harmonic and square-wave reference signals. The results of the optimized system simulations are presented demonstrating good performance of the closed-loop system with nonlinear correction.