What serves as a communications link with authorities controlling navigational flight aspects?

The aircraft radio serves as the primary communications link with authorities who are responsible for controlling navigational aspects of flight. Through the aircraft radio, pilots can communicate with air traffic control (ATC) to receive important instructions, updates on air traffic, weather conditions, and navigational guidance. This communication is essential for maintaining safety and ensuring that flights adhere to established airways and procedures.

Other options, while related to aircraft operation, do not serve this specific function. The transponder transmits information about the aircraft’s position and identification to ATC but does not facilitate direct communication. The flight data recorder captures flight information for analysis after incidents and does not serve as a real-time communication tool. The altimeter measures altitude and provides critical data for flight operations, but it also does not enable communication with authorities. Therefore, the aircraft radio is the correct answer as it is the designated instrument for communicating with controlling authorities regarding navigational flight aspects.