FLC OF AN MLG FAILED TO FOLLOW THE PUBLISHED TRACK DURING A VOR APCH CAUSING ATC TO INTERVENE AND REQUEST AN IMMEDIATE CLB.

Narrative

WE WERE LEVEL AT 4000 FT WHEN CLRED FOR A VOR APCH TO RWY 17L OKC. WHEN WELL WITHIN 5 DEGS OF THE INBOUND COURSE (IN COMPLIANCE WITH THE '5; 5; ALIVE' POLICY USED THROUGHOUT THE INDUSTRY); AND AT A POINT 18.7 DME FROM THE VOR (WHICH IS 10 NM FROM CONGG); WE BEGAN A DSCNT DOWN TO THE NEXT STEP DOWN ALT -- 3300 FT. AT THIS POINT THE CTLR SAW WE WERE APPROX 1 MI OFF CTRLINE AND REQUESTED WE CLB BACK UP TO 4000 FT. WE COMPLIED. THE APCH WAS LATER ABANDONED DUE TO SIGNIFICANT WINDSHEAR IN THE AREA. WE FELT WE MAY HAVE APPEARED OFF CTRLINE TO THE CTLR EVEN THOUGH OUR INSTS INDICATED WITHIN PARAMETERS BECAUSE THE WIDTH OF A RADIAL AT APPROX 17 OR 18 DME IS ABOUT 1800 FT WIDE. 2 OR 3 DEGS AT 18 DME WOULD BE ABOUT 1/2 - 1 MI WIDE. THEREFORE DUE TO THE INCREASING WIDTH OF THE RADIAL; EXTRA CARE/CAUTION SHOULD BE EXERCISED WHEN SHOOTING AN APCH WHERE THE NAV FACILITY IS LOCATED SOME DISTANCE FROM THE ACFT'S POS. THE CTLR DID AN EXCELLENT JOB OF ACCOMMODATING US TO AVOID THE WX IMPACTING THE AREA. HE WAS VERY HELPFUL.