On an ILS, VOR, or NDB approach, when may FMS or GPS guidance be used?

• A. FMS or GPS may be used only as reference and is not the primary navigation on ILS/VOR/NDB approaches
• B. FMS or GPS cannot be used at all on an ILS/VOR/NDB approach
• C. FMS or GPS may be used as primary navigation on ILS/VOR/NDB approaches
• D. FMS or GPS may be used in place of weather information

Answer: (A)

When flying an ILS, VOR, or NDB approach, the published path is defined by the ground-based navaid signals. FMS or GPS can be used to provide reference information and situational awareness—helping you know where you are, how far you are from fixes, and how the approach course lines up with the runway—but the actual navigation guidance that flies the approach remains the conventional navaid signals. In other words, GPS/FMS can assist as a reference, but it is not the primary means of navigation for these traditional approaches.

That’s why using GPS as the sole source to fly the approach isn’t appropriate here, and GPS can’t replace weather information or the ground-based guidance unless you’re executing a procedure specifically designed for RNAV/GPS.