AN ACR LGT TRIED TO NAV PROPERLY IN FOREIGN AIRSPACE WITH ONLY NDB.

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FLT FROM CANCUN TO TPA. NAVING ON UG 765 USING DUAL NDB'S FOR NAV. OUR RMIS (#1 AND #2 ADF NEEDLES) WERE LOCKED ON THE PROPER NDB BEARING INBOUND TO FIS (FISH HOOK NDB). MUHA ADVISED THAT WE WERE 13 MI N OF AIRWAY. ALTHOUGH WE INDICATED ON COURSE; WE DEVIATED BACK TO THE S TO 'CORRECT.' ON OUR PRIOR LEG TO CANCUN; SAME THING OCCURRED FROM MUHA. WHEN TURNING US OVER TO MERIDA CTR; THEY SHOWED US 5 MI DIFFERENT THAN OUR DME (MERIDA CTR WAS RIGHT ON WITH OUR VOR/DME'S). IT SEEMS TO ME THAT MAYBE MUHA'S RADAR MIGHT BE IN NEED OF 'FINE TUNING.' I ALSO REALIZE AT 150 NM FROM AN NDB; 1 NEEDLE WIDTH DEFLECTION IS QUITE A DEV. EVEN WITH OUR NEEDLES CTRED ON PROPER BEARING; IT DOESN'T HAVE 'CDI REFINEMENT' AS WITH VOR'S. IT IS NOT UNUSUAL TO SEE PLUS OR MINUS 2 DEGS VARIATION WITH NDB'S; ESPECIALLY AT FARTHER DISTANCES. SINCE MOST ACFT OPERATE IN THIS AREA WITH INS; IRS; OMEGA; ETC; IT RARELY POSES A PROB. MY ACR'S B727'S HAD THE OMEGAS REMOVED AND OPERATE THESE ROUTES WITH DUAL NDB'S AND VOR WHEN AVAILABLE. IT SHOULD/WOULD BE NICE TO PUT EXTRA POWERFUL VOR'S TO DEFINE THESE LONGER AIRWAY LEG SEGMENTS SO WE COULD USE OUR CDI'S; SINCE MY ACR PROBABLY HAS NO INTENTION TO EVER PUT LONG RANGE NAV ON THE B727'S (PROCESS OF RETIRING THE B727 OVER NEXT 4 YRS). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE B727-200. HIS ACR IS PHASING OUT ALL OF ITS B727'S IN FAVOR OF MORE MODERN ACFT. ALL OMEGA NAV SYS HAVE BEEN REMOVED FROM THE B727'S AS THE OMEGA SYS IS BEING PHASED OUT ALSO. THE RPTR REGRETS THAT THE FISH HOOK (FIS) NDB AND THE KEY WEST (EYW) VOR ARE NOT CO-LOCATED AS ARE THE COZUMEL VOR AND NDB (CZM). THE RPTR BELIEVES THAT THE ONLY REASON THAT THIS NDB PROC IS BEING FLOWN IS BECAUSE 'IT IS LEGAL.' THE RPTR HAS NOT HEARD FROM THE FAA ON THIS MATTER; NOR FROM HIS ACR. THE RPTR ROUTINELY FLIES OUT THE CZM VOR RADIAL AND GETS A 'WAG' FROM THE EYW VOR; BUT THIS IS NOT EXACTLY CORRECT. MUHA DID NOT SEEM TO BE VERY CONCERNED; BUT RELATIONS HAVE DETERIORATED SINCE THIS INCIDENT.