This book systematically presents the operating principles and technical characteristics of the main radio navigating systems (RNSs) that make it possible to adequately evaluate the corresponding scratch indexes and levels of air safety for air vehicles, the chief concern of the International Civil Aviation Organization (ICAO). The book discusses how RNS systems substantially determine navigation accuracy and reliability, and therefore air safety; in addition, it presents practical solutions to problems arising in the operation and development of RNS systems.