The
low-frequency radio range (LFR), also known as the
four-course radio range,
LF/MF four-course radio range,
A-N radio range,
Adcock radio range, or commonly "
the range", was the main
navigation system used by aircraft for
instrument flying in the 1930s and 1940s, until the advent of the
VHF omnidirectional range (VOR), beginning in the late 1940s. It was used for en route navigation as well as
instrument approaches and
holds.