Which avionics system communicates with ground-based ATC facilities?

The communication radio system is essential for communicating with ground-based Air Traffic Control (ATC) facilities. It operates on specific frequencies that allow pilots and air traffic controllers to exchange information such as flight instructions, weather updates, and navigation details. This two-way communication is crucial for maintaining safety in busy airspace, ensuring pilots receive real-time guidance and can respond accordingly.

The other systems mentioned serve different roles. For instance, the navigation radio system is primarily focused on helping pilots determine their position and navigate accurately, rather than facilitating direct communication with ATC. The radar tracking system is used for tracking aircraft positions by ATC but does not actively transmit pilot communication. The transponder system, although vital for identifying an aircraft's location and altitude on ATC radar displays, also does not interact through voice communication with ATC. Hence, the communication radio system is the correct choice for direct interaction with ground-based ATC.