Which transponder mode provides aircraft identification and position only?

• A. Mode A
• B. Mode C
• C. Mode S
• D. Mode M

Answer: (A)

Mode S is the one that carries both identification data and position information. When a Mode S transponder is interrogated, it can provide a unique address and a flight identification (the call sign), and it can also supply additional data such as position (especially with ADS-B or data-link capability). This combination lets air traffic control not only recognize which aircraft is being tracked but also know its precise location.

In contrast, Mode A replies only with a four-digit squawk code that identifies the aircraft to ATC, with no position data. Mode C adds altitude information but does not include identification. Mode M is an older extension that isn’t used for providing a standard identification plus position payload like Mode S.