This paper discusses the electronic navigation systems likely to be found on airline aircraft in the first supersonic era. The trend is toward self-contained navigation systems, probably inertial, for primary navigation. The existing ICAO ground navigation systems will meet any remaining requirements for long-range navigation; VOR/DME and instrument landing will do the job at the terminal ends. The paper deals with the need for back-up station-referenced aids to supplement self-contained navigation systems and reviews the factors which bear on such requirements. The paper deals briefly with all-weather operations requirements and the validity of analytical methods in the development of separation standards.