Which component is NOT required for the ILS to function?

The functionality of the Instrument Landing System (ILS) relies on specific components, including the localizer, glideslope, and outer marker. The localizer provides precise directional guidance to align the aircraft with the runway centerline, while the glideslope assists in maintaining the proper descent angle during approach. The outer marker serves as a positional reference for pilots, indicating when they are at a certain distance from the runway threshold.

Runway threshold markings, while important for visual operations and aiding pilots in identifying the beginning of the runway, are not a required component of the ILS. In low visibility conditions or during precision approaches, the ILS can operate effectively without these markings, as it relies on electronic signals rather than visual cues. Therefore, while they contribute to overall situational awareness and safe operations, runway threshold markings do not impact the primary functioning of the ILS itself.