If the Flight Director (FD) is not engaged and the autopilot button is pressed, what occurs?

When the autopilot button is pressed while the Flight Director (FD) is not engaged, the autopilot system initializes but does not engage in the flight modes. The primary function of the autopilot is to maintain control of the aircraft based on inputs and commands from the FD. If the FD is not active, the autopilot cannot assume control of the aircraft's vertical and lateral flight paths.

The appropriate action is that the autopilot system initializes and awaits engagement, but without the FD being active, it does not take control of the aircraft’s pitch and roll movements. Therefore, simply pressing the autopilot button under these conditions results in the autopilot being set up to engage when the FD is available, but at that moment, it remains inactive.

It's important to recognize that this understanding of the autopilot system functioning is crucial for ensuring that pilots can effectively manage and direct the aircraft, particularly when transitioning between manual and automated flight modes.