Which instrument is primarily used for final approach guidance during an IAP?

The Instrument Landing System (ILS) is primarily used for final approach guidance during an Instrument Approach Procedure (IAP) because it provides precise lateral and vertical guidance to pilots as they approach the runway. The ILS consists of two main components: the localizer, which gives horizontal guidance by aligning the aircraft with the centerline of the runway, and the glide slope, which provides vertical guidance to help maintain the correct descent profile.

This system enables pilots to make final adjustments during the critical phase of landing, especially in conditions of low visibility, ensuring a safe and accurate approach to the runway. ILS approaches are commonly used at airports due to their high accuracy and reliability, making them the preferred choice for final approach guidance in many scenarios. Other instruments like VOR, ADF, and TACAN serve different navigational purposes and may assist in earlier phases of flight or en route navigation, but they do not offer the same level of precision specifically required for final approach.