Transponder
What is transponder?
The transponder is the airborne portion of the Air Traffic Control (ATC) radar beacon system. It receives interrogations from ground radar and replies with a coded signal, allowing controllers to see your aircraft's identity (and, with Mode C, altitude) clearly on their scope. ATC assigns your code (called a "squawk"), and when asked to "ident," pressing the ident button briefly intensifies your return for precise identification. Think of it as your airplane's transmitter that makes you stand out on the controller's screen.
Also known as: xpdr, squawk box, ATC radar beacon system transponder
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