Bonanza 35
Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 34; Flight Crew Total 688; Flight Crew Type 26
Other / Unknown
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Aircraft Equipment Problem Dissipated
ATC Equipment / Nav Facility / Buildings; Aircraft; Human Factors
[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.
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.