Definition
Radar signals displayed on a controller's scope that come from an aircraft's transponder replying to an interrogation, rather than from raw radar energy bouncing off the aircraft's skin. Secondary returns provide identification (aircraft ID), altitude, and other coded data along with position.
Plain English
The blip on a controller's screen that comes from your aircraft's transponder talking back to the radar, not just from the radar pinging off your airframe. It carries extra information like who you are and how high you are.
Context Anchor
Seen in radar and transponder discussions, especially when comparing what ATC can see from a basic radar reflection versus what they can see from a transponder reply.
Derivation
Secondary' here refers to a second, cooperative system layered on top of basic radar. Primary radar simply reflects energy off the aircraft; secondary radar requires the aircraft to actively reply through a transponder. The 'return' is the signal that comes back to the radar antenna.
Why Pilots Care
Secondary returns give controllers reliable identity and altitude information, allowing safer aircraft separation even when primary radar contact is weak.
Intuition Check
Secondary does not mean unimportant or backup here. It means the return comes from the aircraft’s transponder reply rather than from a direct radar reflection.
Example Sentence 1
After the transponder was reset, the controller confirmed good secondary returns showing the correct altitude readout.
Example Sentence 2
Even in heavy precipitation, the secondary returns remained clear on the radar scope.