If RAIM is not available before a GPS approach, what should the pilot do?

When RAIM (Receiver Autonomous Integrity Monitoring) is not available before a GPS approach, the best course of action is to use an alternate navigation system. RAIM is essential for ensuring the integrity and reliability of GPS signals, particularly during precision approaches. Without it, the pilot cannot be sure that the GPS information is accurate or that the system is functioning correctly.

Using an alternate navigation system—such as VOR or NDB—ensures that the pilot can safely navigate to the destination without relying solely on the potentially unreliable GPS data. This approach mitigates risks associated with potential navigation errors or anomalies that could occur if proceeding with the GPS approach without RAIM.

The other choices do not ensure safety. Proceeding with the GPS approach without RAIM (the second option) would mean relying on unverified GPS information, which could lead to navigation errors. Delaying the approach until RAIM is restored (the third option) may not be practical in all situations, especially if other navigation means are available. Switching to VOR navigation (the fourth option) is a good practice, but it is more specific than simply using an alternate navigation system, which opens up broader options for the pilot.