Diagnostic FDM-A method  based on a measurement of frequency modulation of a pulsation component as well as FAM-C method based on a measurement of a alternating current’s frequency have been developed in Air Force Institute of Technology. These methods provide to define a level of a sub-assembly’s abrasive wear and its localization during normal work of a power unit. It is possible to define numerous parameters of bearings and their kinematics pairs as well as a rotor assembly. They are: a level of a bearing rolling friction, smoothness of a bearing cage’s motion, a quantity of a radial clearance. It also provides to detect resonances in elements as well as observe a shape and a relative height of characteristic patterns, from which it is possible to calculate, among others, a quantity of a mechanical quality factor of a kinematics pair – it is possible to define an operating time reserve of the kinematics pair to resonance.