MD11 FLT CREW EXPERIENCES NAV DEVIATION FOLLOWING FMS ANOMALY.

Narrative

IN CRUISE FLT; UNDER RADAR CONTACT; MONTREAL CTR CLRED MD11 DIRECT WAYPOINT (MT) THEN FPR. PF (FO) SELECTED THE 'DIRECT-TO' TILE ON MCDU AND THE 'LSK 1L' NEXT TO (MT). HE VISUALLY CONFIRMED NAV IN ROLL FMA AND (MT) AS ACTIVE WAYPOINT ON NAV DISPLAY. APPROX 30 SECONDS LATER; AFTER SELECTING THE 'PROGRESS' TILE ON THE MCDU; THE PF NOTICED (MT) WAS THE 'FROM' WAYPOINT ON THE MCDU; BUT THE NAV DISPLAY STILL DISPLAYED (MT) AS THE ACTIVE WAYPOINT. HE RE-ACCOMPLISHED THE 'DIRECT-TO' BY TYPING (MT) INTO THE 'DIRECT-TO' BLOCK AND RECEIVED THE CORRECT INDICATIONS ON BOTH THE NAV DISPLAY AND THE MCDU. PF AND PLT MONITORING DISCUSSED THE ANOMALY; CONFIRMING WHAT THEY HAD SEEN AND THAT ALL INDICATIONS APPEARED CORRECT NOW. APPROX 30 MINS LATER; WITH PLT MONITORING (NOW THE CAPT) AND PF (NOW THE RELIEF PLT); ACFT SEQUENCED (MT) AND INITIATED A SLIGHT L TURN TO JOIN J551 TO YVO PER FPR. PLT MONITORING NOTICED ACFT START THE L TURN AND CONFIRMED NAV IN ROLL FMA AND YVO AS ACTIVE WAYPOINT ON THE NAV DISPLAY. APPROX 15 MINS LATER; MONTREAL ASKED WHERE WE WERE GOING. PLT MONITORING NOTED/CONFIRMED NAV IN ROLL FMA AND YVO AS ACTIVE WAYPOINT ON NAV DISPLAY. HOWEVER; WE HAD NO MAGENTA LINE FROM ACFT SYMBOL TO YVO WHICH WAS LOCATED AT 10 O'CLOCK POS AND 90 NM ON THE NAV DISPLAY. MONTREAL TOLD US WE WERE OFF COURSE THEN CLRED US TO A FIX DOWN TRACK. THEY ALSO STATED THEY WOULD RPT THE INCIDENT. AFTER OUR CREW DEBRIEF; 2 LESSONS LEARNED ARE APPARENT: 1) ALTHOUGH WE WERE IN RADAR CONTACT; GREATER DILIGENCE AFTER SEQUENCING (MT) WOULD PROBABLY HAVE ENABLED THE CREW TO DETECT THE ANOMALY AND PREVENT THE NAV ERROR. WE DID CONFIRM NAV AND THE CORRECT ACTIVE WAYPOINT ON THE NAV DISPLAY BUT FAILED TO CATCH THE SUBSEQUENT FMS AUTO SEQUENCE TO A DOWN TRACK WAYPOINT. 2) WHILE THE PF/PLT MONITORING OBSERVED GOOD CRM IN THEIR STATUS BRIEF TO THE PLT RETURNING FROM A REST CYCLE; THEY OVERLOOKED BRIEFING THE PREVIOUS FMS ANOMALY. HAD THEY BRIEFED THIS PROB WE MIGHT HAVE CAUGHT THE SUBSEQUENT ANOMALY AND PREVENTED THE NAV DEV. ALSO OF NOTE; BUT POSSIBLY UNRELATED; THE ACFT EXPERIENCED A LIGHTNING STRIKE ON THE LEG PRIOR TO OURS.