Definition
An aircraft equipped with a functioning transponder that responds to interrogation signals from air traffic control radar, allowing the aircraft to be identified, tracked, and displayed with altitude information on a controller's radar screen.
Plain English
An aircraft carrying working equipment that talks back to ATC radar when the radar pings it, so controllers can see who and where it is and how high it's flying.
Context Anchor
Seen in traffic-alert, collision-avoidance, radar, and electronic surveillance discussions.
Derivation
From Latin 'cooperari', meaning 'to work together.' The aircraft 'cooperates' with the ground radar by replying to its interrogations, rather than just being a passive blip on the screen.
Why Pilots Care
Cooperative aircraft appear reliably on radar and TCAS, improving separation and reducing mid-air collision risk in controlled airspace.
Intuition Check
Do not read “cooperative” as meaning the pilot is being helpful or following instructions. Here it means the aircraft’s equipment is electronically participating so it can be detected.
Example Sentence 1
With a working Mode C transponder, the Cessna was a cooperative aircraft and showed up clearly on the controller's scope with its altitude.
Example Sentence 2
We maintained visual separation from the non-cooperative glider because it did not appear on TCAS.