What is a transponder used for in aviation?

A transponder plays a critical role in aviation communication and navigation. It is an electronic device on an aircraft that receives interrogations from radar systems and responds by transmitting information about the aircraft's position, altitude, and sometimes even its identification. This information is essential for air traffic control (ATC) as it improves the situational awareness of controllers, allowing them to track aircraft more effectively and maintain safe separation.

The transponder also enhances the safety and efficiency of airspace management, particularly in busy air traffic environments. By broadcasting an aircraft's altitude and other vital data, ATC can make informed decisions regarding traffic flow and prevent potential collisions.

The other provided options refer to functions that are unrelated to the primary role of a transponder. Fuel level measurement, visibility during landing, and cabin pressure control involve different systems and equipment designed specifically for those functions within aviation. Understanding the role of a transponder emphasizes its importance in maintaining safety and efficiency in aviation operations.