Under what condition does the ground roll guidance command bar provide Flight Director yaw commands?

The ground roll guidance command bar provides Flight Director yaw commands when a localizer signal is available during takeoff. This is significant because the localizer is a key component of an instrument landing system (ILS), which helps the pilot maintain the proper runway alignment during critical phases of flight, particularly takeoff and landing. When a localizer signal is detected, it indicates that the airplane is aligned with the intended runway centerline, allowing for precise guidance to maintain that alignment.

This function is particularly important during takeoff as it assists pilots in ensuring that the aircraft remains straight down the runway while accelerating. The use of yaw commands in this scenario enhances safety and control, especially in conditions that may otherwise pose challenges to maintaining alignment, such as crosswinds.

In contrast, a non-precision approach, being vectored on downwind, or taxiing in low visibility weather do not necessarily trigger the provision of yaw commands from the Flight Director in the same manner, as they serve different operational contexts or rely on other navigational aids and procedures.