The article is devoted to filtering algorithms that are used to process flight speed data from an inertial navigation system and from a Doppler speed and angle demolition meter. It is shown that the compensation scheme and the filtering scheme, the more common name of which is the complementary filter scheme, are the most common for processing flight and navigational information in inertial-Doppler navigation systems. The paper proves the equivalence of the compensation scheme and the complementary filter scheme, and also substantiates that these schemes, unlike Kalman filtering, are simple to implement, and for design, they require the selection and setting of only one parameter - the filter time constant. A technique for choosing the optimal value of the filter time constant is proposed, which ensures the maximum accuracy of the estimated parameter, namely: the aircraft's cruising speed. The methodology is based on the analysis of error spectra of integrated systems: the inertial system - with a low-frequency error spectrum, and the Doppler system with a high-frequency spectrum. Studies of synthesized filtering schemes have been conducted.