What does SPEED mode cause the Flight Director to maintain?

SPEED mode on the Flight Director system is specifically designed to maintain a selected airspeed. When this mode is activated, the Flight Director will automatically adjust the aircraft's pitch to ensure that it stays at the predetermined airspeed set by the pilot. This feature is crucial during various phases of flight, particularly when managing cruise speeds or during approach and landing scenarios, where maintaining a specific speed is essential for safety and performance.

The focus on maintaining airspeed in SPEED mode allows the pilot to safely manage the aircraft's configuration, ensuring that it does not exceed critical speeds or stall, thereby contributing to a smoother and more controlled flight. The other options listed, such as altitude, pitch attitude, and rate of descent, are controlled by other modes like ALT mode or vertical speed mode, making them not applicable in the context of SPEED mode.