Which NBD is used in conjunction with the ILS?

The correct answer is the Compass Locator, which is often used in conjunction with an Instrument Landing System (ILS) approach. A Compass Locator is a type of radio beacon that provides essential navigation information for aircraft approaching an airport for landing. It operates on low frequency and is designed to guide pilots to safe landing zones by providing a secondary form of navigation.

In the context of ILS operations, the Compass Locator can serve as an additional navigational aid to help pilots establish their position relative to the runway, ensuring an accurate approach path. It functions by transmitting a specific beacon signal that can be picked up by an aircraft's navigation systems, enhancing situational awareness during lower visibility conditions.

Other choices like VOR, Navigation Beacon, and Ground Locator either serve different operational roles or do not directly incorporate the specific purpose of enhancing ILS approach procedures in the same manner as a Compass Locator does.