What approach types cannot include GPS Overlays?

The reason why ILS and LOC approaches cannot include GPS overlays has to do with the nature of these approaches and how they are designed. Instrument Landing System (ILS) and Localizer (LOC) approaches are precision approaches that rely on ground-based navigation systems to provide a defined path for landing. These systems utilize specific radio frequencies to give accurate guidance to the aircraft as it approaches the runway.

In contrast to these precision approaches, GPS overlays typically use a satellite-based navigation system, which provides an alternative means of navigation but is not integrated into the precision guidance offered by ILS and LOC. Since GPS overlays are not designed to be used with the precision guidance of ground-based systems, it results in a lack of compatibility. Therefore, ILS and LOC approaches, being precision approaches reliant on ground systems, do not support GPS overlays.

This distinction is essential for pilots as it indicates the importance of understanding which approaches can utilize GPS technology and which rely solely on traditional ground-based navigation systems.