Which system provides real-time positional information to pilots?

The Global Positioning System (GPS) provides real-time positional information to pilots by utilizing a network of satellites orbiting the Earth. These satellites transmit precise location data, which the aircraft's GPS receiver processes to determine its exact position, speed, and altitude. This data is crucial for navigation, allowing pilots to accurately understand their position relative to waypoints, airways, and airports. In conjunction with other systems like flight management systems, GPS enhances situational awareness and aids in route planning and execution.

While other systems mentioned, such as the autopilot, transponder, and flight data recorder, serve important roles in various aspects of flight operations, they do not provide real-time positional data in the same manner. The autopilot assists in controlling the aircraft's flight path, the transponder communicates the aircraft's position to air traffic control, and the flight data recorder captures flight parameters for post-flight analysis. These functions are critical, but they do not fulfill the specific need for real-time positional information that the GPS system provides.