What was found
IN V-NAV ON CLIMB AND CRUISE THE AIRSPEED WAS STUCK ON 208. ABOUT 10 MINUTES AT CRUISE TRIED V-NAV AGAIN AND IT OPERATED NORMALLY. ACFT GROUNDED. DFCS FLT 1 LOGGED L-NAV ENGAGE FAULT. GROUND VERIFICATION DFCS CURRENT STATUS BITE GRP 10, NO FAULTS. GROUND VERIFICATION TEST, DFCS FMC LRU INTERFACE GRP 34 BITE CKS NORMAL, NR 1 & NR 2 FMCS GROUND VERIFICATION TEST. OPS CKS NORMAL IAW MM 34-61-00-710-801.