A signal generated by which system presents a distinct pattern on an air traffic controller's scope to assist in aircraft identification?

• A. TCAS
• B. Radar altimeter
• C. Transponder
• D. GPS

Answer: (C)

The ability to identify aircraft on the controller’s scope comes from the secondary surveillance radar system, which relies on the aircraft’s transponder. When a ground radar interrogates a transponder, the transponder replies with encoded information such as the assigned squawk code and, if available, altitude. This data creates a distinctive, data-rich target on the controller’s display, making it easy to recognize and identify the specific aircraft among others.

Radar-based primary returns show only echoes and don’t carry identification data, so they’re harder to identify at a glance. The radar altimeter, GPS, and the cockpit TCAS system don’t provide the controller with an identifiable signal pattern on the ATC scope in the same way the transponder does.