Southern Four-Course Radio Range Charts

Beginning in the 1930s, visual guidelines for navigation were replaced by the four-course radio range station system. The radio range station emitted a directional signal, forming four beacons aligned with a compass, each defining a course. Pilots listened to the radio receiver and followed the radio beams from station to station along a particular route. This system had a total of 378 stations before becoming phased out during the 1950s