Definition
Ground-based radar systems that work in conjunction with an aircraft's transponder rather than relying solely on reflected radio energy. The ground radar sends an interrogation signal, and the aircraft's transponder replies with a coded signal that provides identification and, when Mode C or S is used, altitude information to ATC.
Plain English
Radar that asks a question and gets an answer. Instead of just bouncing a signal off the aircraft, it pings the aircraft's transponder, which replies with the flight's identifying code and altitude.
Context Anchor
Seen in discussions of ATC automation, radar displays, transponder use, and how controllers identify aircraft.
Derivation
Beacon' originally meant a signal fire or light used to guide travelers. Here it points to the active reply from the aircraft -- the transponder acts like a small electronic beacon that lights up when interrogated, making the aircraft easy to spot and identify on the controller's screen.
Why Pilots Care
They give controllers reliable identification and altitude information, allowing safer aircraft separation in busy airspace.
Intuition Check
Do not think of a radar beacon as a flashing light. Here, “beacon” means an electronic radio reply that helps ATC identify an aircraft.
Example Sentence 1
Radar beacons let the controller see each aircraft's call sign and altitude on the scope, not just a blip.
Example Sentence 2
Radar beacons provide the data that keeps multiple aircraft safely separated during approach.