ERRONEOUS COORDINATES SET IN INS COMPUTERS. ACFT LANDED AT POINT OF ORIGIN.

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ACFT DEPARTED FUKUOKA; JAPAN; ENRTE TO GUAM. SHORTLY AFTER TKOF A DIFFERENCE BTWN THE INS DISTANCE AND THE DME DISTANCE FROM THE FUKUOKA VOR (DGC) WAS NOTED. DUE TO WX CONDITIONS WHICH REQUIRED SEVERAL DEVS FROM COURSE DURING CLBOUT AND INITIAL CRUISE; WE WERE UNABLE TO FLY OVER A KNOWN FIX SUCH AS A VOR; ETC; TO VERIFY THE ACCURACY OF OUR INS. HOWEVER; BY USING OTHER MEANS OF CHKING (USING THE REMOTE FUNCTION OF THE INS) IT WAS DETERMINED THAT ALL 3 INS UNITS WERE NOT GIVING THE PROPER NAV INFO. WE THEREFORE RETURNED TO FUKUOKA TO DETERMINE CAUSE. IN MY OPINION; THE PROBABLE CAUSE OF THE INS ERROR WAS DUE TO IMPROPER INSERTION FO THE RAMP COORDINATES IN FUK. ALTHOUGH ALL 3 INS UNITS WERE CHKED AND VERIFIED BY BOTH THE CAPT AND FO; THERE IS A STRONG SUSPICION AMONG THIS CREW THAT N3355.8 WAS INSERTED AND VERIFIED BY BOTH MYSELF AND THE FO TOGETHER INSTEAD OF THE CORRECT COORDINATES OF N3335.8. WITH PROPER COORDINATES INSERTED THE FLT RETURNED TO GUAM WITH ALL INS UNITS OPERATING NORMALLY.