Back نطاق راديوي منخفض التردد Arabic Pitkäaaltoradiomajakka Finnish

Low-frequency radio range

White diagram with four rows: first is the letter N followed by a repeating sequence of dash-dot-space; second is the letter A with repeating dot-dash-space; third is A+N followed by a solid line; last line has the word 'time' followed by a right arrow
Low-frequency radio range audio signals: N stream, A stream and combined uniform tone (simulated sounds)

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 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.[1][2][3]

Based on a network of radio towers which transmitted directional radio signals, the radio range defined specific airways in the sky. Pilots navigated using low-frequency radio by listening to a stream of automated "A" and "N" Morse codes. 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.[4][5]

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.[6][2]

  1. ^ Lawrence, Harry (2004). "Airways—from Lighted Beacons to Radio Navigation". Aviation and the Role of Government. Kendall Hunt. p. 92. ISBN 0-7575-0944-4.
  2. ^ a b "Four-Course Radio Range (Low-Frequency Radio Range (LFR))". Museum of Air Traffic Control. Archived from the original on June 22, 2009. Retrieved 2009-07-21.
  3. ^ "The Radio Range". Instrument Flying - AF Manual 51-37. Air Training Command, Department of the Air Force. January 20, 1966. pp. 14/1–17.
  4. ^ Cite error: The named reference onbeam was invoked but never defined (see the help page).
  5. ^ "Four-Course Radio Ranges". www.aopa.org. 1997-05-10. Retrieved 2022-04-05.
  6. ^ Davis, Doug. "Low Frequency Radio Range Locations". Flying the Beams. Retrieved 7 March 2021.
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