Definition
An early form of ground-based radio navigation that broadcast four directional beams from a station, allowing a pilot to follow an airway by listening to Morse code tones. When flying along the course, the pilot heard a steady tone; off course to one side, the pilot heard the Morse letter 'A' (dot-dash); off course to the other side, the Morse letter 'N' (dash-dot). It was the primary airway navigation system in the United States from the 1930s until it was replaced by the VOR system in the 1950s and 60s.
Plain English
An old radio navigation system pilots used to follow airways by ear. If they were on the right path, they heard a steady hum. If they drifted left or right, they heard one of two Morse code letters telling them which way they had wandered.
Context Anchor
Seen in older aviation texts, historical navigation discussions, and explanations of how pilots navigated before modern radio and satellite systems.
Derivation
Named after the two Morse code letters used to indicate which side of the on-course beam the aircraft had drifted to: 'A' (dot-dash) on one side and 'N' (dash-dot) on the other. The two signals interlocked so that when the pilot was exactly on course, the dots and dashes filled each other in to produce a continuous tone.
Why Pilots Care
It provided the first reliable means of following a specific route in low visibility before electronic course-deviation indicators existed.
Intuition Check
Range here does not mean distance. In this term, a radio range is a navigation system that provides course guidance by radio signal.
Example Sentence 1
Before the VOR network was built out, transcontinental airline crews navigated by ear using the A-N radio range.
Example Sentence 2
When the N signal became audible he corrected right to regain the beam.