The paper considers the prevention of nonlinear oscillations of a small unmanned aerial vehicle of a fixed wing (UAV) in a closed loop. This phenomenon is a rapidly developing aircraft oscillations accompanied by increasing amplitude in angular velocities and angles. The pilot can overcome the process of small amplitude oscillations by disconnecting from the control loop. However, since the oscillations begin suddenly and develop so quickly that the pilot does not have time to react. Often these events lead to loss of control and stability of the aircraft. In manned aircraft, this phenomenon has been known since the inception of large aviation. In literature it is called the pilot induced oscillations (PIO) or the aircraft pilot coupling (APC). Oscillations prevention is proposed to be implemented by introducing into the control loop a nonlinear corrective device that provides the control system in question with the desired phase stability margin. Simulation results of pitch angle are presented with active pilot control and the maximum possible time delay and amplitude of input signal.