Definition
A ground-based radar system that detects aircraft by transmitting radio energy and receiving the portion of that energy reflected back from the aircraft's surface. It determines an aircraft's position (range and bearing) without requiring any equipment on board the aircraft to respond.
Plain English
A radar on the ground that bounces a radio signal off an aircraft and uses the returning echo to figure out where that aircraft is. The aircraft does not need to do anything for it to work.
Context Anchor
Seen in instrument flying and air traffic control discussions, especially when learning how ground radar identifies and tracks aircraft.
Derivation
Primary' here means 'first' or 'on its own' -- the radar gets its information directly from the reflected signal, with no help from the aircraft. This contrasts with secondary radar, which relies on a transponder reply from the aircraft.
Why Pilots Care
It lets controllers track aircraft position even if onboard equipment fails.
Analogy
It is like shining a flashlight into a dark room and seeing an object because light bounces back to your eyes. Primary surveillance radar does that with radio energy instead of visible light.
Intuition Check
“Primary” does not mean “best” or “most important” here. It means the radar detects the aircraft directly from reflected radio energy, without needing an electronic reply from the aircraft.
Example Sentence 1
Primary surveillance radar detected the aircraft even though its transponder had failed, allowing the controller to continue providing position information.
Example Sentence 2
Primary surveillance radar provided range and bearing information to guide the flight through the area.