Narrative:

[I] was cleared direct miboe (IAF) for the RNAV 13 approach at D38. I was on autopilot and tracking direct to miboe when ATC called and stated we were off course by 2 miles. Certified garmin 530w showed airplane was tracking properly as did 2 onboard portable GPS units. There were no notams I saw that indicated raim [receiver autonomous integrity monitoring] might be out and the 530w was in approach mode. I relayed my concern and informed ATC that 3 GPS units indicated we were on proper course and heading and had in fact passed over top of miobe and was on course to camey (IAF). ATC canceled approach clearance at this time and issued a heading of 100 and descent to 2;500 to see if contact with surface was possible. The course of 100 took me through the approach course; which I think I communicated to ATC; then to an area northeast of D38. I was over a solid undercast and visual contact with the ground was not possible. I was then asked intentions; requested the approach again and was vectored and cleared for the RNAV 13 approach once more with vectors to camey. This time ATC radar and the onboard GPS seemed to agree and the approach was flown and a missed was declared. When I returned to my home base I reviewed the flight track as recorded on my portable garmin 696 GPS. Its history showed that it was flown directly over miboe and was on course to camey when ATC canceled the approach and issued the 100 heading. My concern is the discrepancy between where approach radar was indicating I was; and where 3 onboard GPS units indicated I was.

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Original NASA ASRS Text

Title: BE35 pilot on approach to D39 via RNAV Runway 13 approach; is informed by ATC that he is two miles off course between MIBOE and CAMEY. Garmin 530w showed airplane was tracking properly as did 2 onboard portable GPS units. Vectors are issued and the next attempt is successful with the GPS units in agreement with ATC Radar.

Narrative: [I] was cleared direct MIBOE (IAF) for the RNAV 13 approach at D38. I was on autopilot and tracking direct to MIBOE when ATC called and stated we were off course by 2 miles. Certified Garmin 530w showed airplane was tracking properly as did 2 onboard portable GPS units. There were no NOTAMs I saw that indicated RAIM [Receiver Autonomous Integrity Monitoring] might be out and the 530w was in approach mode. I relayed my concern and informed ATC that 3 GPS units indicated we were on proper course and heading and had in fact passed over top of MIOBE and was on course to CAMEY (IAF). ATC canceled approach clearance at this time and issued a heading of 100 and descent to 2;500 to see if contact with surface was possible. The course of 100 took me through the approach course; which I think I communicated to ATC; then to an area northeast of D38. I was over a solid undercast and visual contact with the ground was not possible. I was then asked intentions; requested the approach again and was vectored and cleared for the RNAV 13 approach once more with vectors to CAMEY. This time ATC radar and the onboard GPS seemed to agree and the approach was flown and a missed was declared. When I returned to my home base I reviewed the flight track as recorded on my portable Garmin 696 GPS. Its history showed that it was flown directly over MIBOE and was on course to CAMEY when ATC canceled the approach and issued the 100 heading. My concern is the discrepancy between where Approach radar was indicating I was; and where 3 onboard GPS units indicated I was.

Data retrieved from NASA's ASRS site as of July 2013 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.