Narrative:

We were level at 4000 ft when cleared for a VOR approach to runway 17L okc. When well within 5 degrees 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 descent down to the next step down altitude -- 3300 ft. At this point the controller saw we were approximately 1 mi off centerline and requested we climb back up to 4000 ft. We complied. The approach was later abandoned due to significant windshear in the area. We felt we may have appeared off centerline to the controller even though our instruments indicated within parameters because the width of a radial at approximately 17 or 18 DME is about 1800 ft wide. 2 or 3 degrees 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 approach where the navigation facility is located some distance from the aircraft's position. The controller did an excellent job of accommodating us to avoid the WX impacting the area. He was very helpful.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.