Which instrument is primarily guided by the localizer?

The Course Deviation Indicator (CDI) is primarily guided by the localizer, which is part of the Instrument Landing System (ILS). The localizer provides lateral guidance to the aircraft, indicating whether it is left or right of the intended approach course. The CDI displays this information, allowing pilots to adjust their heading to align with the localizer. When flying an ILS approach, the CDI helps pilots navigate precisely to the runway by showing their position relative to the centerline of the localizer signal.

Understanding how the CDI interacts with the localizer is crucial for pilots, as it facilitates a safe and accurate approach to landing, particularly in conditions of low visibility. The other instruments mentioned do not provide this lateral guidance: the Vertical Speed Indicator measures rate of climb or descent, the Attitude Indicator shows the aircraft's orientation relative to the horizon, and the Airspeed Indicator indicates the speed of the aircraft. Each of these instruments plays a specific role in flight but does not relate directly to the localizer function in precise navigation approaches.