Narrative:

IFR flight plan. Departed pne to hgr. Given routing mxe V474 scape direct. Modena was notamed unusable. Using RNAV kns-80. 5 NM prior to mxe cleared direct delro. Set up off lrp 248 degree radial 18 NM since mxe unusable. 10 NM west of mxe given vector southwest for spacing and then was turned direct drlro. Set up correctly as noted above. ATC called and advised 4 NM off course, although HSI showed centered. Rechked RNAV setting and continued. ATC then advised aircraft was off course to the northwest and gave radar vectors. Continued radar vectors to scape. RNAV was then set to lrp or ths. Pointer 20 degrees to the right of course compared to #2 VOR set on ths up until noeno at which point it corrected to agree with #2 VOR. At scape set RNAV to hgr off ths. Accurate to landing. The thing that bothered me was that even though the RNAV was obviously off by 20 degrees, there was no indication whatsoever. The needles and flags showed a correct course. Trying to reconcile course and exact position off the airway was very difficult given the location. Once on the airway, it became clear how far the RNAV was off (other actions). Once the discrepancy was first noted by ATC, I should have asked for vectors, until I worked out the discrepancy.

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Original NASA ASRS Text

Title: PLT OF AN SMT PVT ACFT FAILED TO FOLLOW IFR CLRNC ROUTING TRACK DUE TO A FAULTY RNAV RADIO RECEIVER INDICATOR.

Narrative: IFR FLT PLAN. DEPARTED PNE TO HGR. GIVEN ROUTING MXE V474 SCAPE DIRECT. MODENA WAS NOTAMED UNUSABLE. USING RNAV KNS-80. 5 NM PRIOR TO MXE CLRED DIRECT DELRO. SET UP OFF LRP 248 DEG RADIAL 18 NM SINCE MXE UNUSABLE. 10 NM W OF MXE GIVEN VECTOR SW FOR SPACING AND THEN WAS TURNED DIRECT DRLRO. SET UP CORRECTLY AS NOTED ABOVE. ATC CALLED AND ADVISED 4 NM OFF COURSE, ALTHOUGH HSI SHOWED CTRED. RECHKED RNAV SETTING AND CONTINUED. ATC THEN ADVISED ACFT WAS OFF COURSE TO THE NW AND GAVE RADAR VECTORS. CONTINUED RADAR VECTORS TO SCAPE. RNAV WAS THEN SET TO LRP OR THS. POINTER 20 DEGS TO THE R OF COURSE COMPARED TO #2 VOR SET ON THS UP UNTIL NOENO AT WHICH POINT IT CORRECTED TO AGREE WITH #2 VOR. AT SCAPE SET RNAV TO HGR OFF THS. ACCURATE TO LNDG. THE THING THAT BOTHERED ME WAS THAT EVEN THOUGH THE RNAV WAS OBVIOUSLY OFF BY 20 DEGS, THERE WAS NO INDICATION WHATSOEVER. THE NEEDLES AND FLAGS SHOWED A CORRECT COURSE. TRYING TO RECONCILE COURSE AND EXACT POS OFF THE AIRWAY WAS VERY DIFFICULT GIVEN THE LOCATION. ONCE ON THE AIRWAY, IT BECAME CLR HOW FAR THE RNAV WAS OFF (OTHER ACTIONS). ONCE THE DISCREPANCY WAS FIRST NOTED BY ATC, I SHOULD HAVE ASKED FOR VECTORS, UNTIL I WORKED OUT THE DISCREPANCY.

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.