What was found
DURING CRUISE, FMC LIGHT ILLUMINATED AND VTK WAS DISPLAYED ON CAPTAINS INBD DISPLAY. F/O FMC NAV DISSAPEARED AND LT NAV V, NAV DISCONNECTED. IT RETURNED TO NORMAL AFTER ABOUT ONE MINUTE. ACFT GROUNDED. PERFORMED BOTH LT AND RT FMC BITE IAW FIM 34-61, TASK804. FMC NR 1 AND NR 2 FAULT LEG 1 INFLT FAULTS. NR 2 FMC ALT DEACTIVATION USED IAW CHAPTER 5, TABLE 3, ITEM 1. R & R NR 1 FMC IAW AMM 34-61-02. REF MIG-2A 11247656 FOR NR 1 FMC SOFTWARE INSTALLATION. FMC PN VARIFIED EFFECTIVE FOR ETOPS. SEAM-C MARK NOTIFIED. ALT. DEACTIVATION REVERSED. ETOPS SIGNIFICANT SYS VARIFICATION ACCOMPLISHED FOR BOTH NR 1 AND NR 2 FMC REF AMM 34-61-00-710-801. OPS CKS GOOD, BOTH NR 1 AND NR 2 FMC.