ERRONEOUS FMC POS INFO CAUSES A TERRAIN WARNING AFTER TKOF. THE RAW DATA POS WAS CONFIRMED AND USED FOR NAV WITH THE ASSISTANCE OF ATC FOR A SUCCESSFUL FLT FROM THE DOMINICAN REPUBLIC.

Narrative

LEAVING SDQ TODAY WE HAD A BIT OF A NAV PROB. THE COORDINATES WERE ENTERED AT THE GATE AND VERIFIED BY EACH PLT. NO PROBS. TAXI; CAPT IN EPGWS; FO IN MAP; HIS LEG. NOTHING UNUSUAL ABOUT THE FLT UNTIL WE LIFTED OFF ON RWY 17 (IMMEDIATELY OVER THE SHORE AND OVERWATER) WHEN WE RECEIVED A 'TERRAIN TERRAIN' WARNING. IN CLR WX WE KNEW SOMETHING WAS WRONG. I SWITCHED OVER TO MAP MODE ON CLBOUT AND REALIZED THE PINK LINE HAD SHIFTED OUT TO THE W OF OUR POS. RAW DATA CONFIRMED THAT THE POS THE FMC WAS INCORRECT AND WE PROCEEDED TO FLY VIA RAW DATA. WE TOLD LAS AMERICAS CTL WE WERE HAVING DIFFICULTY WITH OUR ONBOARD FLT COMPUTER AND THEY SAID 'OK.' WHEN LAS AMERICAS GAVE US DIRECT TO 'RETAK' POS; ONCE WE WERE ON A NBOUND HEADING; WE TOLD THEM UNABLE AND ASKED THEM FOR A HEADING. WE WERE TUNING AND XCHKING EVERY RADIAL AND DME AS POSSIBLE; AND IT CONFIRMED THAT WHERE WE WERE AND WHERE THE ACFT THOUGHT IT WAS; WERE 2 DIFFERENT PLACES. LAS AMERICAS GAVE US A HEADING; AND VERIFYING THE RADIALS; DISTANCES ON THE DME'S; AND ADF'S WE APCHED RETAK; CALLED PORT-A-PRINCE AND NAVED THROUGH THEIR AIRSPACE ON THE A363 USING THE PTA 301 DEG RADIAL. SHORTLY AFTER WE CONTACTED ZMA AND TOLD THEM WE WERE HAVING DIFFICULTIES AND THEY CHANGED OUR FILED NAV CAPABILITIES TO THE ACR. THEY GAVE US HEADINGS. WE VERIFIED POS AGAIN USING THE RAW DATA METHODS. FORTUNATELY MANY ADF'S WERE WORKING ALONG THE RTE. AT XA53Z MIAMI GAVE US A LATITUDE/LONGITUDE POS AND WE COMPARED WHAT THE FMC SAID; ACTUAL N2209 W07435; FMC N2236 WO7433; THE 2 POS ABOUT 30 MI APART. WE NOTIFIED DISPATCH OVER ACARS; AND PER ADVICE TRIED TO REMOTELY TUNE NEARBY VORS; BUT DIDN'T HELP. AFTER LNDG WE LEFT THE FMCS ON AND SHOWED AVIONICS WHAT WE HAD. AT THE GATE; THE FIX PAGE IN THE FMC HAD MIA SHOWING 022 DEGS/20 KTS WITH A 9 NM DRIFT RATE. SUPPLEMENTAL INFO FROM ACN 536914: THE PROB SEEMED TO ARISE DURING THE TKOF PROFILE; AT THE POINT WHERE THE FMCS SNAPSHOT RWY HEADING AT GND BREAK. THAT WAS WHEN EVERYTHING WENT HAYWIRE. DURING THE FLT; WE TRIED REMOTE TUNING THE VORS VIA THE VOR CTL HEADS AND TUNING THEM VIA THE FMC PROGRAM PAGE TO REALIGN THE MAPS PER INSTRUCTIONS FROM MAINT AND DISPATCH. THIS HAD NO EFFECT AND THE MAPS NEVER CORRECTED THEMSELVES. CALLBACK CONVERSATION WITH THE FO REVEALED THE FOLLOWING INFO: THE FO RPTED THAT MAINT FOUND NO DEFINITIVE PROBS AND WOULD MONITOR THE ACFT.