As part of the synthesis of a tracking system for unmanned aerial vehicles (UAVs) under the action of external uncontrolled disturbances and incomplete measurements of the state vector, the structure of the observation subsystem, which includes two state observers, was developed. The first observer gives estimates of the velocities based on measurements of the UAV mass center coordinates. The second observer on the measurement of tracking errors gives estimates of mixed variables (functions of state variables, external influences and their derivatives) for which feedback is formed.