Internal functions automatically monitor individual satellite failures and the integrity of GPS signals. If a failure is detected, up to [6] minutes is allowed to re-acquire GPS signals. If the GPS cannot be recovered, GPS PRIMARY LOST is displayed and a smooth transition occurs to navigation using DME/DME or VOR/DME radio position updates - if available. If radio updates are not available (e.g., out of range) NAV ACCURACY OWNGRADE and IRS ONLY NAVIGATION messages will be displayed in the scratchpad if certain other conditions are met.
