EXTENDED OVERWATER DC10 PIC RPTS INS EQUIP PROBS NECESSITATING REROUTING CAUSING FUEL USAGE CONCERNS. COMPANY COORD EXPEDITED HANDLING WITH ZMP DUE TO FUEL CONCERNS APPARENTLY FAILS TO MATERIALIZE.

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FLT WAS DISPATCHED OUT OF EHAM WITH #3 INS INOP. FLT WAS NORMAL TO LEVELOFF AT FL300 AND WE WERE DIRECT TO RODSI ON A COURSE ABOUT PARALLEL TO UP1. AFTER LEVELOFF WITH ALERT FOR RODSI AND CHKING THE NEXT POINT ON OUR NAV (GIVEM); SCOTTISH GAVE US DIRECT ERAKA. AFTER THE FO ENTERED ERAKA; HE NOTICED THE FLAGS FOR THE NAV ON HIS HSI VOF FLAG WERE NORMAL. THE FLAGS IN NAV INDICATE THE INFO FROM THE INS IS FLAWED; NOT ACCEPTABLE. REVIEWING MINIMUM EQUIP FOR THE AIRSPACE WE WERE IN; THE FO REQUESTED FL280 TO GET US BELOW MNPS/RVSM AIRSPACE. THE SO AND I WERE WORKING ON A PHONE PATCH TO FLT CTL AND MAINT CTL TO DISCUSS OUR OPTIONS FOR CONTINUING OR RETURNING. FLT CTL SAID WE COULD CONTINUE ON A RTE OVER SUM; KEF; 63N30W; 61N40W; OZN; 59N50W; PRAWN; YDP; ETC; TO DLH FLT PLAN RTE. THE CONCERNS OF THE CREW WERE TWOFOLD. FIRST; WITH 1 INS; WE ARE VERY LIMITED FOR NAV. THE REST OF THE FLT WAS ROUTINE UNTIL SWITCHING TO ZMP. WITH THE FIRST ISSUE IN MIND; RYKAVICK CTL OFFERED US DIRECT 63N30W WHEN WE WERE IN RADAR CONTACT; BUT WE TURNED IT DOWN DUE TO CONCERN OVER POSSIBLE OTHER PROBS; IE; LOSS OF RADAR OR LOST COM. WE LOOKED AT LEG LENGTHS TOO LONG FOR NAV WITH VOR AND/OR ADF AND IF THE LAST INS FAILED; WE WOULD BE DEAD RECKONING. THE SECOND CONCERN COMES FROM LACK OF REASONABLE HANDLING BY ZMP AND APCH CTL. FLT CTL HAD COORDINATED A SHORTCUT TO SAVE 800 LBS OF FUEL BECAUSE THE NEW RTE USED MUCH OF OUR CONTINGENCY FUEL. WHEN WE GOT TO THE LAST ZMP SECTOR AFTER CHANGING TO THE EAU 6 ARR OVER TWINZ; WE WERE SLOWED AND VECTORED TO USE MORE THAN OUR 800 LBS SAVED FUEL TO FOLLOW ALL OTHER ACFT INBOUND (4) AND ENDED ON A 12 MI FINAL WITH NO TFC AHEAD. SO MUCH FOR COORD OR COOPERATION.