MD-83
Flight Crew Commercial
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Flight Crew Overcame Equipment Problem
Aircraft
Shortly after departure; talking to LAX Center got an 'RNP' flag in both PFD's. During our evaluation of the problem and verifying our position; LAX Center called and questioned our position and gave us a heading. Informed ATC our FMS wasn't working properly and changed our flight plan designation.
We flew the rest of the fight using VOR to VOR navigation (old school). Flight landed uneventfully.
An MD-80 flight crew reported a malfunctioning FMS to ATC; and they flew VOR-based navigation to destination.