Which of the following is NOT a flight director lateral mode?

The correct choice is CRUISE because it is not classified as a lateral mode of operation for a flight director. In aviation, lateral modes are primarily responsible for controlling the aircraft's direction or heading.

HDG (Heading) mode allows the flight director to command the aircraft to maintain a specific heading, whereas ROLL mode engages the mechanisms necessary to bank the aircraft in the desired direction. APPR (Approach) mode facilitates the aircraft's lateral guidance during an approach to landing, ensuring alignment with the runway.

In contrast, CRUISE mode typically refers to a flight condition or phase where the aircraft maintains a steady altitude and speed, rather than specifically addressing lateral maneuvering. Hence, it is not categorized as a lateral mode for flight directors.