Definition
An aircraft that does not carry an operating transponder, or whose transponder is not functioning, so it cannot automatically reply to interrogations from secondary surveillance radar or air traffic control radar systems. Such an aircraft can still be detected by primary radar, which bounces a signal off the airframe, but it does not transmit identification, altitude, or other coded information back to controllers.
Plain English
An airplane that doesn't have a working transponder, so it can't 'talk back' to radar. Controllers may still see it as a blip, but they don't get its altitude or identity automatically.
Context Anchor
Seen in discussions of radar, traffic displays, collision-avoidance equipment, and traffic detection around airports or in controlled airspace.
Derivation
From 'cooperative,' meaning working together. A cooperative aircraft replies to radar interrogations and helps the controller identify it. A non-cooperative one does not respond, so the radar system has to work harder on its own.
Why Pilots Care
Affects collision avoidance and the quality of traffic information available from ATC.
Analogy
It is like someone in a group who is present but not answering when their name is called. They are still there, but the system asking for a response gets little or nothing back.
Intuition Check
“Non-cooperative” does not mean the pilot is being unhelpful or refusing instructions. It means the aircraft is not providing the electronic signal that a detection or traffic system expects.
Example Sentence 1
With its transponder failed in flight, the Cessna became a non-cooperative aircraft and showed up only as a primary target on the controller's scope.
Example Sentence 2
Pilots flying VFR should stay alert for non-cooperative aircraft that may not appear on traffic displays.