Transponder
Definition
An electronic device on an aircraft that receives radar signals and automatically transmits a response with identification and altitude information back to air traffic control.
Related Terms
Squawk Code
A four-digit code assigned by ATC and entered into an aircraft's transponder for identification on radar. Special codes include 7500 (hijack), 7600 (radio failure), and 7700 (emergency).
TCAS (Traffic Collision Avoidance System)
An aircraft system that monitors nearby aircraft transponder signals and provides resolution advisories (climb/descend) to prevent mid-air collisions, independent of air traffic control.
Radar Vectoring
The process of providing navigational guidance to aircraft by ATC through specific headings (vectors) based on radar observation. Used to sequence arriving aircraft and maintain separation.