HDG TRACK DEV.

Narrative

THE PROB AROSE FROM AN INCORRECT PRESENT POS ENTERED IN THE FMS COMPUTER. APPARENTLY THE FUTURE DEST WAS ENTERED AS OUR PRESENT POS; MAKING THE MAP OF OUR RTE ON OUR NAV DISPLAY BACKWARD. AFTER TKOF; THE DEP CTLR CLRED US TO 10000 FT AND 'CLRED ON COURSE.' AS THE PNF; I SLUED THE FLT DIRECTOR HDG BUG TOWARD THE FIRST FIX ON OR RTE OF FLT AS DEPICTED ON THE NAV DISPLAY; NOT REALIZING IT WAS TAKING US IN THE OPPOSITE DIRECTION OF OUR INTENDED DEST. WHEN THE DEP CTLR ASKED US WHY WE WERE ON A S- WERLY COURSE VICE A N-EERLY COURSE; WE IMMEDIATELY REALIZED OUR MAP DISPLAY WAS BACKWARDS AND TURNED TOWARDS OUR DEST USING NORMAL NAV MEANS. THIS IS ONE OF THOSE MISTAKES MADE BY RELYING SOLELY ON COMPUTER GENERATED NAV. A COMPUTER IS ONLY AS GOOD AS THE INFO IT IS GIVEN (GARBAGE IN/GARBAGE OUT). SOME CONTRIBUTING FACTORS INVOLVED WERE; IT WAS THE LAST LEG OF A 5 LEG; 12 HR DAY. BOTH OF US WERE TIRED AND READY TO GET TO OUR LAYOVER. BEING A VERY QUICK TURN AROUND; THE CAPT LOADED THE FMS WHILE I DID THE WALKAROUND. GETTING BACK IN THE COCKPIT; I WAS IN A HURRY TO GET THINGS READY FOR OUR DEP AND DIDN'T BOTHER CHKING THE FMS PROGRAM. ANOTHER FACTOR WHICH CAME INTO PLAY WAS A RWY CHANGE ON TAXI OUT. I PUT THE NEW DEP RWY IN THE FMS BUT DID NOT HIT 'RWY UPDATE' UPON TAKING THE RWY; THEREBY STILL LETTING THE COMPUTER THINK IT WAS AT OUR DEST. ALTHOUGH THERE WAS NO CONFLICT; IT WAS EMBARRASSING TO TURN IN THE TOTAL OPPOSITE DIRECTION THAN WE WERE EXPECTED. IN THE FUTURE I WILL ALWAYS CHK THE FMS AND CORRELATE IT WITH THE MAP DISPLAY; NO MATTER HOW TIRED I AM OR HOW QUICK THE TURN AROUND.