In the paper the oscillatory modes of a non-autonomous flight control system are considered. The phenomenon of pilot induced oscillations in the presence of non-linearities such as "saturation" and backlash in the system is studied under conditions of active control and a significant value of the time delay. The conditions for the occurrence of self-oscillations are established, using the harmonic stationary method, the robustness of forced oscillations in the first harmonic approximation in the class of amplitudes and frequencies of the reference signal is studied.