Definition
A ground-based radar system used by air traffic control that works together with a transponder in the aircraft. The ground radar sends an interrogation signal; the aircraft's transponder receives it and replies with a coded signal that gives the aircraft's identity (via assigned squawk code) and, if Mode C is installed, its pressure altitude. This produces a much stronger, clearer return on the controller's display than primary (skin-paint) radar alone.
Plain English
A radar setup where the ground station asks each aircraft 'who are you and what altitude?' and the aircraft's transponder answers automatically. That answer shows up on the controller's screen as a tagged target rather than just a blip.
Context Anchor
You will see ATCRBS discussed in transponder use, radar services, ATC identification, and altitude reporting.
Derivation
The name describes the system literally: a 'radar beacon' is an aircraft-mounted device that, when interrogated by radar, sends back its own signal — like a lighthouse that only flashes when asked. This is why ATCRBS targets are so much brighter and more informative on the screen than passive radar returns.
Why Pilots Care
Provides controllers with reliable aircraft identification and altitude data beyond what primary radar alone can show, reducing separation errors in controlled airspace.
Intuition Check
Do not think of “beacon” here as a flashing light. In ATCRBS, the aircraft acts like an electronic beacon by sending a radio reply back to ATC.
Example Sentence 1
Because the aircraft's transponder was responding to ATCRBS interrogations, the controller could see its altitude and call sign on the radar display.
Example Sentence 2
During the IFR flight, ATCRBS replies allowed ATC to maintain positive radar contact through the busy terminal area.