Definition
A radar beacon is a system in which a ground-based interrogator transmits a coded signal that triggers a coded reply from a transponder on board the aircraft. The reply is received by the ground station and displayed on the controller's radar scope, providing positive aircraft identification, altitude information, and a stronger return than primary skin-paint radar alone.
Plain English
A back-and-forth radio system between the ground radar and a small transmitter in the aircraft. The ground sends a question, the aircraft answers, and the controller sees a clear blip with the aircraft's identity and altitude.
Context Anchor
You may hear or see this term in ATC radar procedures, transponder discussions, or explanations of how controllers identify aircraft on radar.
Derivation
The word beacon comes from Old English beacen, meaning a signal or sign — originally a fire lit on a hill to signal others. In radar use it keeps that idea: the aircraft's transponder acts as an active signal-sender that responds whenever the ground radar interrogates it, rather than just passively reflecting energy.
Why Pilots Care
Radar beacon replies give controllers positive identification and altitude information, allowing safe aircraft separation and efficient routing in controlled airspace.
Intuition Check
Do not read beacon here as only a flashing light on an airport. In radar, beacon means an electronic reply from the aircraft’s transponder.
Example Sentence 1
After the transponder failed, the controller advised that beacon radar coverage was lost and only a primary target remained on the scope.
Example Sentence 2
With the beacon operating in Mode C, the radar display showed both the aircraft's position and its current altitude.