Which of the following is NOT used by the FMS position to determine aircraft location?

• A. VHF
• B. VOR/DME
• C. GPS
• D. ILS

Answer: (D)

Understanding how the Flight Management System determines position relies on signals that provide actual location data. GPS gives precise latitude and longitude, while VOR/DME provides a bearing from a VOR station and a distance from a DME to fix the aircraft’s position. VHF navigation signals underpin those VOR-based methods, so they are indeed used to determine where you are.

ILS, however, is an approach navigation aid that provides a localizer signal for lateral guidance and a glideslope for vertical guidance to the runway. It doesn’t supply a continuous position fix for en-route navigation or feed the FMS with a reliable position data source. Its purpose is to help fly the approach, not to determine the aircraft’s location in space for the FMS. That’s why ILS is not used by the FMS to determine location.