Definition
A ground-based radar system that works together with airborne transponders to identify and track aircraft. The ground station sends out an interrogation signal; the aircraft's transponder receives it and replies with a coded signal containing the aircraft's identity (squawk code) and, if equipped with Mode C, its pressure altitude. Unlike primary radar, which depends on a radio echo bouncing off the aircraft's skin, ATCRBS depends on the aircraft actively replying. This produces a stronger, more reliable target on the controller's display, along with the data tag showing who and how high.
Plain English
A radar setup where the ground station asks aircraft 'who are you and how high?' and each aircraft's transponder answers back. The controller then sees a clear blip on the screen with the aircraft's ID and altitude attached.
Context Anchor
You may see ATCRBS in AIM and radar service discussions, especially when reading about transponders, aircraft identification, altitude reporting, and controller radar displays.
Derivation
The name describes the system: 'secondary' radar, because it works alongside primary (skin-paint) radar; 'beacon' because the aircraft's transponder acts like a beacon, actively signaling back rather than just reflecting. 'Secondary' here doesn't mean less important — it means the second of two cooperating systems.
Why Pilots Care
Enables positive aircraft identification and automatic altitude reporting, allowing ATC to maintain safe separation without relying solely on primary radar returns or voice position reports.
Analogy
It is like someone calling your name and you answering back with your name tag and height. Primary radar only notices that something is there; ATCRBS gets an active reply from the aircraft.
Intuition Check
“Secondary radar” does not mean less important radar. It means radar that depends on an aircraft’s automatic reply, rather than only on a reflected radar signal.
Example Sentence 1
Because the aircraft's transponder was inoperative, ATCRBS could not display its altitude, and the controller asked the pilot to report level passing each thousand feet.
Example Sentence 2
ATCRBS replies provide both identity and Mode C altitude information directly to the radar facility.