Narrative:

After being vectored north of pcw in IMC WX ZOB controller turned us toward 'kukaf' initial approach fix and cleared us for the GPS runway 27 approach at pcw. I have not done many GPS only approachs and it had been some time since I had been cleared toward an IAF for a full procedure. Upon reaching kukaf IAF on a southeasterly heading, I turned 30 degrees left to fly a teardrop 'hold in lieu of pt' entry. I failed to account for our approach toward the IAF from a position north of the inbound/outbound course. Therefore, my 30 degree left turn made us roughly parallel to the inbound course (269 degrees) now south of inbound course-line, but thinking I was north of it. I began a right turn as if to enter holding pattern. My right turn, in reality, took me further south off course. Unaware of exactly how far south off course I was, I continued the approach, descending at the appropriate distances from the runway, but never truly established inbound on the approach. I would now estimate I crossed kukaf approximately 2-3 mi south of the fix. Got back on course by FAF ('hozde') and landed normally. ZOB didn't seem to notice, or declined to say anything. Human factors contributing to my mistake were: 1) being unprepared mentally for full procedure non precision approach. 2) lack of experience with GPS equipment (in this case, a northstar 'M3' GPS receiver). 3) my inability or lack of recent experience in 'mental math' to allow me to quickly determine my distance off course based on the GPS display of 'bearing to' information about my desired fix. 4) my decision to 'get the job done' despite the fact that I could not easily calculate my position error. Had I known I was about 3 mi south of desired track I would have been far more likely to ask for vectors to the FAF or a missed approach. 5) my belief (in this case, correct) that I would see the airport after reaching MDA. Again, I was unaware of my position error's size. If I had needed to guess my position error while in-flight, I might have guessed between a few hundred feet and a quarter mi. I didn't really discover the size of my position error until 30 mins later, when I thought through my vectors and subsequent turns. My remedy shall be to attain better understanding of the GPS function of the M3 unit, and to practice numerous overlay approachs in VMC before accepting another true IMC GPS approach.

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Original NASA ASRS Text

Title: AN OFF COURSE DSCNT TO MDA LIMITS BY A BE9L PIC WHEN HE GETS CONFUSED AS TO HIS POS RELATIVE TO THE APCH COURSE FOR THE GPS RWY 27 AT PCW, OH.

Narrative: AFTER BEING VECTORED N OF PCW IN IMC WX ZOB CTLR TURNED US TOWARD 'KUKAF' INITIAL APCH FIX AND CLRED US FOR THE GPS RWY 27 APCH AT PCW. I HAVE NOT DONE MANY GPS ONLY APCHS AND IT HAD BEEN SOME TIME SINCE I HAD BEEN CLRED TOWARD AN IAF FOR A FULL PROC. UPON REACHING KUKAF IAF ON A SOUTHEASTERLY HEADING, I TURNED 30 DEGS L TO FLY A TEARDROP 'HOLD IN LIEU OF PT' ENTRY. I FAILED TO ACCOUNT FOR OUR APCH TOWARD THE IAF FROM A POS N OF THE INBOUND/OUTBOUND COURSE. THEREFORE, MY 30 DEG L TURN MADE US ROUGHLY PARALLEL TO THE INBOUND COURSE (269 DEGS) NOW S OF INBOUND COURSE-LINE, BUT THINKING I WAS N OF IT. I BEGAN A R TURN AS IF TO ENTER HOLDING PATTERN. MY R TURN, IN REALITY, TOOK ME FURTHER S OFF COURSE. UNAWARE OF EXACTLY HOW FAR S OFF COURSE I WAS, I CONTINUED THE APCH, DSNDING AT THE APPROPRIATE DISTANCES FROM THE RWY, BUT NEVER TRULY ESTABLISHED INBOUND ON THE APCH. I WOULD NOW ESTIMATE I CROSSED KUKAF APPROX 2-3 MI S OF THE FIX. GOT BACK ON COURSE BY FAF ('HOZDE') AND LANDED NORMALLY. ZOB DIDN'T SEEM TO NOTICE, OR DECLINED TO SAY ANYTHING. HUMAN FACTORS CONTRIBUTING TO MY MISTAKE WERE: 1) BEING UNPREPARED MENTALLY FOR FULL PROC NON PRECISION APCH. 2) LACK OF EXPERIENCE WITH GPS EQUIP (IN THIS CASE, A NORTHSTAR 'M3' GPS RECEIVER). 3) MY INABILITY OR LACK OF RECENT EXPERIENCE IN 'MENTAL MATH' TO ALLOW ME TO QUICKLY DETERMINE MY DISTANCE OFF COURSE BASED ON THE GPS DISPLAY OF 'BEARING TO' INFO ABOUT MY DESIRED FIX. 4) MY DECISION TO 'GET THE JOB DONE' DESPITE THE FACT THAT I COULD NOT EASILY CALCULATE MY POS ERROR. HAD I KNOWN I WAS ABOUT 3 MI S OF DESIRED TRACK I WOULD HAVE BEEN FAR MORE LIKELY TO ASK FOR VECTORS TO THE FAF OR A MISSED APCH. 5) MY BELIEF (IN THIS CASE, CORRECT) THAT I WOULD SEE THE ARPT AFTER REACHING MDA. AGAIN, I WAS UNAWARE OF MY POS ERROR'S SIZE. IF I HAD NEEDED TO GUESS MY POS ERROR WHILE INFLT, I MIGHT HAVE GUESSED BTWN A FEW HUNDRED FEET AND A QUARTER MI. I DIDN'T REALLY DISCOVER THE SIZE OF MY POS ERROR UNTIL 30 MINS LATER, WHEN I THOUGHT THROUGH MY VECTORS AND SUBSEQUENT TURNS. MY REMEDY SHALL BE TO ATTAIN BETTER UNDERSTANDING OF THE GPS FUNCTION OF THE M3 UNIT, AND TO PRACTICE NUMEROUS OVERLAY APCHS IN VMC BEFORE ACCEPTING ANOTHER TRUE IMC GPS APCH.

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.