What must be set for an A320's autothrust system to function properly?

The autothrust system on the A320 is designed to operate in conjunction with the flight director (FD) system. For autothrust to function properly, it's essential that at least one flight director is engaged. The flight director provides the necessary guidance for maintaining the aircraft's intended flight path and assists in managing power outputs appropriately.

When one of the flight directors is on, it ensures that the autothrust system can effectively respond to the flight management system’s commands, thus optimizing performance and enhancing safety during various phases of flight, including takeoff, climb, cruise, and approach. This functionality allows the autothrust to adjust thrust levels automatically based on the aircraft's needs, improving efficiency and reducing pilot workload.

In contrast, it is not strictly required for both thrust levers to be in a specific detent, such as CLB or MCT, for the system to engage. Similarly, while the ENG MODE selector being set to NORM is essential for proper engine operation, it does not directly correlate to the fundamental requirements for autothrust activation.