Definition
Directional radio signals transmitted from ground-based navigation stations along a defined course or path, used by aircraft receivers to determine position relative to that course and to navigate along it.
Plain English
Invisible radio signals sent out from a station on the ground in a specific direction. An aircraft picks up the signal and uses it as a line in the sky to follow.
Context Anchor
Seen in instrument approach and HUD discussions, where cockpit guidance may be based on radio signals that define the path toward a runway.
Derivation
The word 'beam' comes from the Old English 'bēam' meaning a tree or a long straight piece of wood, later extended to mean a ray of light or a narrow directed signal. In navigation, a 'radio beam' borrows that idea -- a narrow, directional path of radio energy that an aircraft can follow like a line drawn through the sky.
Why Pilots Care
They provide the precise guidance path the HUD uses to show whether the aircraft is on or off the correct approach course.
Intuition Check
Do not picture a visible beam like a spotlight. Here, a radio beam is an invisible signal pattern used for navigation guidance.
Example Sentence 1
The pilot tracked the radio beam from the VOR to stay on the airway centerline.
Example Sentence 2
The pilot adjusted heading to recapture the radio beams before reaching the final approach fix.