LTT CHARTER FLT HAS 20 MI NAV ERROR DUE TO OMEGA VLF STATION BEING SHUT DOWN WITH NO NOTICE AND FREQ REASSIGNED TO HAWAII.

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NAV DEV DUE TO VLF/OMEGA POS ERROR. CLBING OUT OF SCOTTSDALE; AZ; AT APPROX 15000 FT; WE WERE CLRED DIRECT TO ZUN VOR. WE WERE BELOW THE ALT WHERE WE COULD RECEIVE ZUN VOR SO WE WERE NAVING SOLELY BY THE GLOBAL GNS-500 VLF/OMEGA. EITHER ZAB OR PHX DEP INFORMED US THAT WE WERE ABOUT 20 DEGS OFF ON HDG FOR ZUN. AT THE TIME THE GLOBAL WAS SHOWING A 120 KT XWIND AND WE INFORMED DEP/CTR THAT COULD BE PART OF THE CONFUSION. THE NEXT SECTOR INFORMED US THAT WE WERE 20 MI W OF OUR INTENDED COURSE AND GAVE US A HDG FOR ZUN. WHEN WE WERE ABLE TO RECEIVE ZUN VOR WE SAW THAT WE WERE IN FACT OFF COURSE. WE INITIALIZED THE GLOBAL OVER ZUN AND HAD NO MORE PROBS ON THE FLT. ON THE RETURN FLT WE WERE TALKING TO ZDV AND RECEIVED CLRNC DIRECT FROM THE DENVER AREA TO INW VOR. AGAIN WE WERE OUT OF RANGE OF THE INW VOR AND WERE NAVING BY THE GLOBAL UNIT. CTR INFORMED US THAT WE WERE 15 DEGS OFF OF A HDG DIRECT TO INW AND WE CORRECTED. WHEN WE GOT WITHIN RANGE OF A VOR WHERE WE COULD CHK OUR POS WE DISCOVERED WE WERE OFF COURSE BY 28 NM. NORMAL PROC FOR US IS TO INITIALIZE THE UNIT AT THE DEP ARPT. THIS WAS DONE IN BOTH CASES. BECAUSE THE ARPT REF POINT CAN BE AS MUCH AS 2 MI FROM THE END OF THE RWY; WE USUALLY REINITIALIZE THE UNIT AT THE FIRST VOR THAT WE CROSS OVER. IN BOTH CASES WE WERE CLRED DIRECT TO ANOTHER VOR BEFORE REACHING A VOR TO REINITIALIZE THE UNIT. USUALLY THIS MEANS THAT WE COULD BE UP TO 2 MI OFF; BUT WE ARE ABLE TO CORRECT THIS ONCE WE ARE IN RANGE OF THE VOR. THE UNIT IS BEING SENT TO MAINT BECAUSE WE HAVE HAD PROBS OF THIS SORT ONCE BEFORE. ONE UNUSUAL FACTOR WAS ON THE FIRST LEG WE HAD NO PAX AND WE MADE A 45 DEG BANK; 120 DEG TURN AFTER DEP WHEN GIVEN A NEW HDG. PERHAPS THE GLOBAL COULD NOT FOLLOW SUCH A RAPID HDG CHANGE? NOTE: THE PROB WAS APPARENTLY DUE TO THE ANNAPOLIS VLF BEING TAKEN OFF THE AIR AND ITS FREQ REASSIGNED TO THE HAWAII VLF (SEE ENCLOSED NOTICE). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES FOLLOWING SUGGESTION FROM THE MANUFACTURER; THE COMPANY DESELECTED BOTH ANNAPOLIS AND HAWAII STATIONS. THERE WERE 5 STATIONS IN THE SYS AND THE DESELECT LEAVES 3 TO WORK WITH. THIS SHOULD ALLOW A NAV ERROR THAT IS ACCEPTABLE; NOT AN ERROR OF 20 MI.