What does "transponder mode C" indicate?

• A. The transponder is providing altitude information along with identification
• B. The transponder is inoperable and not transmitting
• C. The transponder is only providing identification data
• D. The transponder is providing emergency signal

Answer: (A)

Transponder mode C is used in aviation to indicate that the aircraft is not only transmitting its identification code but also its altitude information to air traffic control. This mode enhances situational awareness by allowing controllers to see an aircraft's altitude in addition to its location, enabling more efficient and safer air traffic management. The information provided by mode C is critical for maintaining safe separation between aircraft, especially during approach and landing phases.

In contrast, other options describe different conditions or functions of a transponder. For example, if the transponder were inoperable and not transmitting, it would not be providing any information at all, including altitude or identification. Similarly, if the transponder were only providing identification data, it would be operating in mode A, not mode C. Lastly, an emergency signal would typically involve a specific set of squawk codes associated with distress situations, which is separate from the standard operation of providing altitude information. Therefore, the uniqueness of mode C lies in its dual capability of relaying both identification and altitude data.