B767-300 CAPTAIN REPORTS MAP SHIFT AT IAD FOLLOWING LONG DISTANCE FLT.

Narrative

WE WERE ON A VISUAL APCH TO IAD RWY 19L; AFTER A RWY CHANGE DUE TO FLT Z GOING AROUND FROM A MISALIGNED APCH TO RWY 1R. ON DOWNWIND TO RWY 19L WE RPTED THE ARPT IN SIGHT AND RECEIVED AND ACKNOWLEDGED CLRNC FOR VISUAL TO RWY 19L; MAINTAIN 3000 FT UNTIL BASE AND CALL TWR. I TURNED BASE APPROX 5 MI AND HAD FO EXTEND RWY 19L ON THE LEGS PAGE. I WAS USING THE FMC DATA TO PROPERLY ALIGN FOR FINAL APCH. THE FO PICKED UP THE RWY AFTER I HAD UNDERSHOT RWY 19L WHILE FOLLOWING THE FMC GENERATED PICTURE AS I DID NOT HAVE THE RWY IN SIGHT. I DISCONNECTED THE AUTOPLT AND ALIGNED THE ACFT WITH RWY 19L. AT THIS TIME WE NOTICED A MAP SHIFT OF APPROX 3 MI. I CONTINUED WITH ALL CONFIGNS AND CHKLISTS AND WAS STABILIZED AT APPROX 800 FT AGL. AT 500 FT AGL WE RECEIVED 'TOO LOW GEAR; GS; GS AND GAR COMMANDS.' WE (3 PLTS) CONFIRMED PROPER CONFIGN AND PROFILE AND CONTINUED TO A LNDG. I ATTRIBUTED THE COMMANDS TO MAP SHIFT. I ASKED TWR TO NOTIFY FLT Y OF THE MAP SHIFT; AND IN THE CREW ROOM THEY EXPERIENCED THE SAME EVENT. I BELIEVE FLT Z ALSO HAD A MAP SHIFT; THEREBY CAUSING HIS MISALIGNMENT AND GAR. FOR 3 COMPANY ACFT RETURNING TO IAD AFTER 10 HR FLTS AND ALL EXPERIENCING MAP SHIFT AT THE ARPT SEEMS UNUSUAL. THE FMC COMPUTED DISPLAY HAD BEEN ACCURATE THE ENTIRE FLT SINCE DEP FROM ZZZ.