During a GPS approach, which alternate instruments and ground stations must be operational?

• A. None of them are required; monitoring is recommended
• B. VOR and ILS must be operational
• C. DME must be operational
• D. WAAS must be operational

Answer: (A)

The key idea is that a GPS approach can be flown with GPS as the sole navigational source; there’s no requirement to have other ground-based nav aids operating just to execute the approach. You rely on the GPS system for guidance, and you should actively monitor its integrity (keep an eye on GPS status and any RAIM checks) and cross-check with the cockpit instruments as available. If GPS integrity were ever suspect, you’d revert to other navigation sources or go missed, but there’s no mandate that VOR, ILS, DME, or WAAS be operational simply to fly the GPS approach.