If Receiver Autonomous Integrity Monitoring (RAIM) is not available prior to beginning a GPS approach, what should the pilot do?

When Receiver Autonomous Integrity Monitoring (RAIM) is not available, the reliability of the GPS signal cannot be guaranteed, which is critical for the safety and accuracy of an approach procedure. RAIM ensures that the positional information provided by GPS is accurate and provides alerts if the integrity of the signal is compromised. Without this assurance, the pilot should revert to a navigation system other than GPS, which offers a higher level of reliability for conducting the approach.

Using a non-GPS navigation system ensures that the pilot has a dependable means of navigating, especially during critical phases of flight such as approaches and landings. This choice promotes safety by avoiding reliance on a system that lacks the necessary integrity monitoring.

In this context, while utilizing GPS for the approach might seem possible, it becomes risky without RAIM verification, as it could lead to incorrect navigation. Continuing with the GPS approach without RAIM monitoring could jeopardize safety, and merely notifying air traffic control may not be sufficient in ensuring safe operations without an alternative navigation system. Thus, opting for a different navigation system serves as the best course of action under these circumstances.