Narrative:

We were on a training/currency flight practicing instrument approachs in a technically advanced airplane. We activated ILS runway 35R approach to centennial airport on GPS1 (a garmin 430) and switched the navigation source to VLOC1. Upon being vectored onto final; we noticed that the course on the HSI (an avidyne entegra pfd) was 260 degrees; not the correct course of 347 degrees. The separate hdi and vdi provided valid navigation indications for the localizer/GS and GPS1 indicated the correct dtk to the next waypoint. However; the erroneous course on the HSI was extremely confusing to the PF. We changed the HSI navigation source to GPS1; and this reset the HSI to the correct final approach course (347 degrees). Switching back to VLOC1 maintained the correct course on the HSI. We think the errant final approach course remained from the previous approach flown (ftg ILS 26). Since we were practicing in VFR conditions; this flight was not in danger. However; we are concerned about this condition occurring in IFR; and we discussed how we would handle that situation after completing the flight. We did not report the incident to maintenance because we thought it was a freak occurrence not easily reproduced. We submit the report to NASA in the event other such situations are observed and an alert to operators is deemed necessary.

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Original NASA ASRS Text

Title: AN SR22 PILOT USING AN ADVANCED NAVIGATION SYSTEM FINDS THAT IT DOES NOT FUNCTION AS HE EXPECTED DURING A PRACTICE INSTRUMENT APPROACH.

Narrative: WE WERE ON A TRAINING/CURRENCY FLT PRACTICING INST APCHS IN A TECHNICALLY ADVANCED AIRPLANE. WE ACTIVATED ILS RWY 35R APCH TO CENTENNIAL ARPT ON GPS1 (A GARMIN 430) AND SWITCHED THE NAV SOURCE TO VLOC1. UPON BEING VECTORED ONTO FINAL; WE NOTICED THAT THE COURSE ON THE HSI (AN AVIDYNE ENTEGRA PFD) WAS 260 DEGS; NOT THE CORRECT COURSE OF 347 DEGS. THE SEPARATE HDI AND VDI PROVIDED VALID NAV INDICATIONS FOR THE LOC/GS AND GPS1 INDICATED THE CORRECT DTK TO THE NEXT WAYPOINT. HOWEVER; THE ERRONEOUS COURSE ON THE HSI WAS EXTREMELY CONFUSING TO THE PF. WE CHANGED THE HSI NAV SOURCE TO GPS1; AND THIS RESET THE HSI TO THE CORRECT FINAL APCH COURSE (347 DEGS). SWITCHING BACK TO VLOC1 MAINTAINED THE CORRECT COURSE ON THE HSI. WE THINK THE ERRANT FINAL APCH COURSE REMAINED FROM THE PREVIOUS APCH FLOWN (FTG ILS 26). SINCE WE WERE PRACTICING IN VFR CONDITIONS; THIS FLT WAS NOT IN DANGER. HOWEVER; WE ARE CONCERNED ABOUT THIS CONDITION OCCURRING IN IFR; AND WE DISCUSSED HOW WE WOULD HANDLE THAT SITUATION AFTER COMPLETING THE FLT. WE DID NOT RPT THE INCIDENT TO MAINT BECAUSE WE THOUGHT IT WAS A FREAK OCCURRENCE NOT EASILY REPRODUCED. WE SUBMIT THE RPT TO NASA IN THE EVENT OTHER SUCH SITUATIONS ARE OBSERVED AND AN ALERT TO OPERATORS IS DEEMED NECESSARY.

Data retrieved from NASA's ASRS site as of January 2009 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.