Low-frequency radio range

The low-frequency radio range, 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 <a href="/facts/Radio_navigation/sRkrEaG9">navigation system</a> used by aircraft for <a href="/facts/Instrument_flight_rules/RPfLUgbe">instrument flying</a> in the 1930s and 1940s, until the advent of the <a href="/facts/VHF_omnidirectional_range/XV2txX9M">VHF omnidirectional range</a> (VOR), beginning in the late 1940s. It was used for en route navigation as well as <a href="/facts/Instrument_approach/UDS9QFWr">instrument approaches</a> and <a href="/facts/Holding_(aviation)/nBmxNcPC">holds</a>.
Based on a network of radio towers which transmitted <a href="/facts/Radiation_pattern/5t0QU2mv">directional</a> radio signals, the radio range defined specific <a href="/facts/Airway_(aviation)/aQgk7LDK">airways</a> in the sky. Pilots navigated using low-frequency radio by listening to a stream of automated "A" and "N" <a href="/facts/Morse_code/GXwCl1HV">Morse codes</a>. For example, they would turn or slip the aircraft to the right when hearing an "N" stream ("dah-dit, dah-dit, ..."), to the left when hearing an "A" stream ("di-dah, di-dah, ..."), and fly straight ahead when these sounds merged to create a constant tone indicating the airplane was directly tracking the beam.
As the VOR system was phased in around the world, low-frequency radio range was gradually phased out, mostly disappearing by the 1970s. There are no remaining operational facilities today. At its maximum deployment, there were over 400 stations exclusively using low-frequency radio range in the Continental U.S. alone.

Low-frequency radio range open-in-new

Low-frequency radio range