Which system is vital for selecting flight parameters and modes in an aircraft?

The Auto Flight System is essential for selecting flight parameters and modes in an aircraft because it integrates various functionalities that control the aircraft’s flight envelope. This system includes not only autopilot capabilities that maintain a set flight path but also allows the pilot to engage and manage different flight phases such as climb, cruise, and descent.

By utilizing inputs from the aircraft’s navigation systems and pilot commands, the Auto Flight System automatically adjusts the aircraft's speed, altitude, and heading to optimize performance and safety. It empowers pilots to focus on overall flight management while automating routine tasks, thus enhancing the operational efficiency of the aircraft.

For the other systems listed, while they play important roles, they do not primarily manage flight parameters and modes. The Flight Data Recorder serves to capture flight information for post-flight analysis, the Throttle Control System manages engine thrust but lacks the broader functions of mode selection, and the Engine Management System focuses on optimizing engine performance rather than handling flight parameters directly.