navigatinguserafourcourserange

The four-course radio range was introduced in 1928 as a form of radionavigation for aircraft. Each range station creates four courses at 90 degree angles to each other. An experienced navigator could determine whether he was on one of the four courses and, if not, to which side of it he was. Locating a station near an airport and lining up one of the four courses with the runway provided a primitive form of instrument approach that was instrumental in permitting scheduled flights that only rarely were delayed due to weather.

In 1941, more sophisticated radionavigation systems that could provide more accurate bearings (and more than four courses) were introduced. Finally, in 1974, the last operational four-course range station was shut down. As of this writing (October 2010) only one four-course range station exists, and it operated by a hobbyist.