FLC OF LGT NAVING BY ADF WAS ADVISED BY MUHA CENTER THEY WERE 15 MI N OF COURSE.

Narrative

THIS WAS A FLT FROM TAMPA; FL; TO CANCUN; MEXICO. WHEN NAVING ON B646 FROM FISH HOOK (FIS) TO ROBIN INTXN; THE NAV IS ACCURATE ONLY TO VINKA INTXN. AFTER THAT; FIS TAKES YOU N OF THE AIRWAY; EVEN THOUGH FIS SHOWS YOU STILL ON COURSE. THIS HAS BEEN VERIFIED BY CANCUN (CUN) DME AND HAVANA CENTER. UPON REACHING THE CUN 011 DEG RADIAL; THE CUN DME IS 122 MI; 36 MI N OF COURSE. ALL THE TIME; FIS SHOWS US ON COURSE. AT NO TIME COULD WE RECEIVE MERIDA (MIO); THE OTHER END OF THE AIRWAY. ALSO; STARTING ABOUT 150 MI OUT FROM FIS; THERE IS ANOTHER STATION IDENTIFIER ON THE FREQ; MAKING IT DIFFICULT TO HEAR THE FIS IDENT. THE SECOND IDENT SOUNDED LIKE W-Z-M. THIS IS THE SECOND TRIP I'VE MADE TO CANCUN AND I'VE HAD THIS PROBLEM BOTH TIMES. THIS IS MY SECOND NASA RPT ON THE SUBJECT. PERHAPS THIS RTE NEEDS TO BE CHKED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ANALYST AND RPTR DISCUSSED A NORMAL ERROR IN READING BUTT END OF NEEDLE FLYING OUT FROM ADF STATION AS MUCH AS 200 MI. HIS COMPANY HAD NOT OFFERED ANY INFO ON VARIATION ERROR PASSING THROUGH 2 OR 3 DEGS OF VARIATION CHANGE. RPTR PLANS TO DISCUSS WITH HIS CHIEF PLT.