What was found
PDIS 584 34-58 3994 07APR23 ANC OPEN U LOGPAGES:367021 UNABLE RNP BEFORE TAKEOFF. RNP WAS 1.10 AND INCREASED TO 4.0. SPOKE WITH MOCC AND DISPATCH. CHOSE TO PROCEED. EVERYTHING WAS NORMAL UNTIL APPROX 5K FEET. GIVEN DIRECT TO NODLE AND AIRCRAFT SHOWED A MAGENTA LINE FROM THE NORTH. AIRCRAFT ND HEADING WAS APPROX 20* OFF MAG HDG AND ATC MATCHED MAG HDG. IRUS SHOWED NO DRIFT RATE OR GROUND SPEED DURING FLIGHT BUT SHOWED IT ON GND BEFORE AND AFTER T.O. ACFT HDG WAS UP TO 45* OFF BY THE TIME WE LANDED. GNS 1 & 2 FAIL STATUS MSG. DUMPED APPROX 44K LBS OF FUEL AND RETURNED. ILS HARD TUNED AND FUNCTIONED. FACT 08APR23 18:06 ANC AMM: 34-63-01-4 AMM: 34-63-06-3 REMOVED AND REPLACED FMCS #1 & #2 IAW MD11 AMM 34-63-01-4. SOFTWARE UPLOADED IAW MD11 AMM 34-63-06-3. OPS CHECKED GOOD. ALIGNED IRUS, ENABLED GNS NAV AND ANP RATE MAINTAINED 0.01NM ON BOTH FMC READOUTS. A/C READY FOR SERVICE