What was found
PRIOR TO REACHING OCEANIC CROSSING ENTRY POINT, RECEIVED C.G. OUT OF AFT LIMITS ALERT WITH CG SHOWING 41.5 CONCURRENTLY RECEIVED SET LANDING ELEV. LOST PR OF, FMS SPEED AND NAV ON BOTH AUTOPILOTS. STARTED CH ECK LIST- ALERTS DISAPPEARED. ABOUT 10 TO 15 MINUTES LATER, SAME ALERTS REPEATED FOR APROX 5 MINUTES. CONSULTED WITH DUTY OFFICER AND MOCC. BOTH FMC'S APPEARED TO BE FAILING PER MOCC. ALL CONCURRED DIVERT TO KBOS BEST COURSE OF ACTION. REMOVED AND REPLACED BOTH FMCS PER AMM 34-63-01-4 AND 34-63-05-3 AND RTS PASSED FOR BOTH UNITS.