The system uses RAIM to assess the integrity of GPS signals. The 'UNABLE RNP' annunciation will be displayed on the PFW if either the system Estimated Position Error (EPE) is greater than the required RNP, or if GPS integrity is insufficient while the aircraft is inbound to the FAF. The RNP level is displayed in amber whenever the 'UNABLE RNP' annunciation is displayed. If the FAF waypoint is sequenced while this condition persists, a system message to abort the approach will be generated.