The flight director (FD) overlays visual cues, typically crosshairs or a V-bar, onto the primary flight display or artificial horizon. It calculates exactly how the aircraft should be maneuvered to follow a programmed route, intercept a localizer, or maintain an altitude. Pilots follow the FD's guidance manually or engage the autopilot to follow it automatically.
Heard on the job
Keep the FD centered during the approach and you'll break out right on the centerline.
Insider tip
A common rookie mistake is fixating on the flight director bars instead of scanning the raw data instruments to ensure the aircraft is actually doing what it is supposed to.