THE SIMILAR SOUNDING COGAN NDB AND THE COLSN RADAR FIX ON THE ILS RWY 16 TO MANASSAS; VA; CAUSE CONFUSION TO A PLT UNFAMILIAR WITH THE AREA LEADING TO A TRACK DEV THAT IS CAUGHT IN A TIMELY FASHION BY POTOMAC APCH.

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HAVING JUST BEEN TURNED OVER TO POTOMAC APCH CTL ENRTE FROM PALWAUKEE ARPT (CHICAGO); I WAS INSTRUCTED TO FLY DIRECT TO A FIX AND THENCE CLRED FOR THE ILS RWY 16L APCH AT MANASSAS; VA. I HAD BEEN HAVING SOME RADIO DIFFICULTIES ON THIS TRIP; AND I MISUNDERSTOOD THE INITIAL APCH FIX TO BE COGAN RATHER THAN THE CORRECT COLSN. UNABLE TO FIND IT QUICKLY ON MY CHARTS; I LOOKED IT UP IN A DIRECTORY I CARRIED; AND DIALED IT INTO MY NAV RADIO. IN AS MUCH AS THE INDICATED DISTANCE TO THE FIX WAS LESS THAN 10 NM; THIS SEEMED REASONABLE AND I HEADED TO COGAN. THOUGH THE HEADING WAS AWAY FROM MANASSAS; IT WASN'T SO FAR AS TO BE OUT OF THE REALM OF POSSIBILITY; AND I HAVE FLOWN SIMILAR; CIRCUMSPECT ROUTES MANY TIMES BEFORE WHILE BEING VECTORED ON APCH. IT WASN'T UNTIL A COUPLE OF MINS LATER; WHEN ATC QUERIED MY HEADING AND REITERATED THE COLSN FIX THAT I REALIZED THAT I WAS HEADED TO THE WRONG FIX. I WAS ABLE BY THIS TIME (ONLY 2 OR 3 MINS LATER) TO LOCATE COLSN; BUT NEITHER THE ENRTE LOW ALT CHART OR THE APCH PLATE FOR THE ILS RWY 16L APCH SHOW ANY COORDINATES FOR THIS FIX. I ASKED FOR AND RECEIVED A HEADING TO FLY; AND WAS SUBSEQUENTLY VECTORED TO THE LOC COURSE; AND CONTINUED TO AN UNEVENTFUL LNDG AT MANASSAS. IT IS UNFORTUNATE THAT THESE 2 FIXES HAVE SIMILAR SOUNDING NAMES; AND EVEN MORE SO THAT ATC WOULD CLR AN ACFT TO A FIX THAT WITHOUT ANY PUBLISHED DATA TO ALLOW ONE TO FLY DIRECT; NO RANGE/RADIAL; OR LATITUDE/LONGITUDE. UNDOUBTEDLY; THIS IS A WELL USED RTE INTO THE DC AREA. THIS IS PROBABLY A SIMPLE OVERSIGHT THAT COULD BE EASILY RECTIFIED BY PUBLISHING THE INFO; IN ONE FORM OR ANOTHER; ON BOTH CHARTS.