Definition
A radar system in which the aircraft carries a transponder that, when interrogated by a ground radar pulse, transmits a coded reply back. The reply is much stronger than a normal radar reflection and includes identification and altitude information, allowing controllers to see the aircraft clearly on their radar display along with its identity and altitude.
Plain English
A two-way radar setup. The ground radar sends out a signal, and a small unit in the aircraft answers back with a stronger signal that tells the controller which aircraft it is and how high it is flying.
Context Anchor
Seen in air traffic control, radar, transponder, and some navigation aid discussions.
Derivation
Radar comes from 'radio detection and ranging.' A beacon is a signal sent out to be seen or noticed — historically a fire or light to guide travelers. So a radar beacon is a device that sends out a radio signal in response to radar, making the aircraft easier to 'see' on the controller's screen.
Why Pilots Care
Enables positive aircraft identification and altitude reporting on ATC radar without depending only on weak primary radar returns.
Intuition Check
A radar beacon is not a flashing light you look for outside the airplane. In this context, “beacon” means an electronic responder that sends back a radio signal.
Example Sentence 1
The controller asked the pilot to recycle the transponder because the radar beacon reply had dropped off the scope.
Example Sentence 2
Without a working radar beacon reply, the controller saw only a primary radar target and could not confirm the aircraft's altitude or call sign.