B767 FLT CREW REPORTS MISSING CROSSING RESTRICTION DUE TO FMC DROPPING ROUTE DURING DESCENT AND CREW CHANGE IN LFFF AIRSPACE.

Narrative

WHILE DSNDING FROM FL390 TO CROSS ANG VOR AT FL280; THE CTR AUTOPLT WENT INTO DEGRADED MODE. THIS OCCURRED JUST AS THE IRO AND THE CAPT WERE PREPARING TO SWITCH AFTER THE CAPT'S REST PERIOD. I HAD JUST COPIED THE ATIS AND WAS GETTING OUT THE PLATES FOR LFPG. THE IRO WAS SELECTING THE APCH IN THE FMC. THE VERT SPD WINDOW OPENED TO 1400 FPM. NO VNAV OR LNAV AND WE WERE IN HDG HOLD. AT THE SAME TIME THE FMC DUMPED OUR RTE SHOWING ONLY LFPG AS OUR ACTIVE WAYPOINT. THE IRO WAS IN THE L SEAT; I WAS IN THE R SEAT; AND THE CAPT WAS DIRECTING FROM A STANDING POS BTWN THE TWO OF US. WE PUT ANG BACK IN AND IT BECAME THE ACTIVE WAYPOINT BUT BY THIS TIME WE WERE COMING CLOSE TO THE VOR. THEN THE CAPT DIRECTED THE IRO TO RESELECT THE ARR. THIS BEING DONE THERE WAS STILL A GAP BTWN THE ACTIVE WAYPOINT AND THE FIRST POINT ON THE ARR. THE IRO WAS NOW FLYING THE AIRPLANE TO KEEP US CLOSE TO OUR COURSE WHILE I RELOADED THE AIRWAY TO CONNECT THE ACTIVE WAYPOINT AND THE FIRST FIX ON THE ARR. THIS GOT OUR RTE BACK BUT BY THIS TIME WE WERE RIGHT ON TOP OF OR A LITTLE PAST THE ACTIVE WAYPOINT OF ANG. LNAV REENGAGED SO THE AIRPLANE; OF COURSE; WANTED A R TURN BACK TO THE FIX WHEN WE NEED A L TURN TO INTERCEPT. THE IRO DID A GOOD JOB KEEPING THE AIRPLANE HEADED IN THE CORRECT DIRECTION. I THEN SELECTED INTERCEPT LEGS TO OUR NEXT FIX; THE FIRST FIX ON THE ARR. THE IRO SET ABOUT A 15 DEG INTERCEPT FOR THE FIX AND NOW LNAV HAD A GOOD RTE IN THE BOX AND SOON CAPTURED THE COURSE. WE REESTABLISHED OURSELVES ON THE AIRWAY AND WERE ON ALT. HOWEVER; BY THIS TIME WE HAD MISSED OUR XING ALT AND MISSED OUR TURN. I AM NOT EXACTLY SURE BY HOW MANY FEET; BUT I WOULD GUESS ABOUT 2000-2500 FT OVER THE VOR. AS FOR THE TURN IT DID NOT APPEAR WE HAD GONE TOO FAR ASTRAY BY THE TIME WE TURNED TOWARDS THE AIRWAY AND REESTABLISHED OURSELVES. WE QUICKLY GOT THINGS SORTED OUT; RECONFIRMED THE ALT WITH ATC AND WERE BACK ON THE CORRECT PATH AND ALT. THE WHOLE THING PROBABLY TOOK BTWN 1-2 MINS. ATC MADE NO COMMENT ONE WAY OR THE OTHER AND THERE WERE NO OTHER ACFT OBSERVED ON THE ADS-B. WHEN WE ARRIVED AT LFPG; THE CAPT WROTE UP THE EVENT AND MAINT DEFERRED THE CTR AUTOPLT. THE MECH SAID HE THOUGHT WE HAD LOST AN FCC BECAUSE IT WAS NOT RECEIVING GOOD UPDATES. I REALLY AM NOT SURE OF HIS DIAGNOSIS BECAUSE OF THE LANGUAGE BARRIER DURING HIS TALK WITH THE CAPT. WE FLEW THE NEXT LEG WITH THE CTR AUTOPLT DEFERRED AND THINGS WENT AS NORMAL. I AM REALLY NOT SURE WHY THE FMC WOULD HAVE DUMPED OUR RTE AND THE CTR AUTOPLT QUIT. THE TIMING OF THE EVENT COULD NOT HAVE BEEN MORE INOPPORTUNE. IT SEEMED LIKE SOMETHING FROM A VERY BUSY AQP SIMULATION PERIOD. THE COMBINATION OF HAVING THE CREW IN TRANSITION; DSNDING; SETTING UP FOR THE ARR/APCH; LOSING THE AUTOPLT AND THE RTE ALL IN ONE SHOT MADE IT A CHALLENGE. I DO THINK WE WERE ABLE TO WORK WELL AS A CREW AND GET THE AIRPLANE SAFELY BACK ON COURSE AND ALT WHILE REESTABLISHING OUR DATA IN THE FMC. BOTTOM LINE; HOWEVER; IS WE DID INDEED MISS AN ALT AND A TURN.