What happens when there are 5 satellites visible regarding RAIM?

When there are five satellites visible, fault detection is enabled in the context of Receiver Autonomous Integrity Monitoring (RAIM). RAIM is a system used in GPS navigation that assesses the integrity of the position data provided by the satellites.

With five satellites in view, the GPS receiver can compare the information from these satellites to identify any discrepancies. This capability allows the receiver to detect faults or errors in the navigation solution. Fault detection means that the system can determine if a satellite is providing unreliable data, even if it cannot necessarily identify which satellite is faulty.

This is crucial for maintaining safety and accuracy during flight operations, especially in IFR conditions. Having a sufficient number of satellites improves the system's reliability, which is why five satellites can enable fault detection rather than fault exclusion or isolation, which would require more sophisticated methods or a different number of satellites to fully achieve.