What does Mode C transmit in a transponder system?

Mode C transmits altitude data from the aircraft's altimeter, providing critical information about the aircraft's pressure altitude above sea level. This mode is part of the transponder system used in aviation to enhance situational awareness for both pilots and air traffic controllers. When the transponder is set to Mode C, it automatically sends this altitude information to ground radar systems, which helps in tracking the aircraft's vertical position and ensures safe separation between aircraft.

The other options focus on different types of information that may not be transmitted in Mode C. For instance, aircraft identification relates more closely to Mode A, which provides the squawk code assigned by air traffic control. Enhanced data for ADS-B falls under more advanced systems like ADS-B Out, which provides additional positional and velocity data beyond what is provided by Mode C. Positioning data for navigation primarily involves GPS data and doesn’t pertain to the specific function of Mode C in transponder systems.