Which mode allows the Garmin 330W to transmit altitude information to air traffic control?

• A. Standby Mode
• B. Mode C
• C. Mode S
• D. Test Mode

Answer: (B)

The correct answer is Mode C. This mode allows the Garmin 330W transponder to transmit the aircraft's altitude information to air traffic control and other aircraft equipped with altitude reporting transponders. Mode C sends a three-dimensional position report that includes both the aircraft's location and its altitude, which is crucial for air traffic management and maintaining safe separation between aircraft.

In more detail, when operating in Mode C, the transponder automatically responds to interrogations from air traffic control radar with information that includes the aircraft's altitude above mean sea level, enabling controllers to track aircraft and provide adequate spacing. This mode is widely used in controlled airspace and is required for flights in certain airspace classes.

Other modes, like Standby Mode, do not actively transmit any data, while Mode S provides more advanced functionalities, including selective addressing and improved communication capabilities, but it primarily differs from Mode C in its operational scope. Test Mode is typically used for testing the transponder’s functionality and does not transmit altitude data relevant for air traffic control operations. Thus, Mode C specifically fulfills the requirement for altitude transmission.