Narrative:

For about 8 months I have noticed that phoenix VOR has had an anomaly in the northeast quadrant. Coming in on the fossl 2 arrival, the course deviation indicators for both navigation receivers have fluctuated plus or minus 5 degrees. This occurs from 30-60 NM out and from FL250 and below. This has happened in different aircraft and to both navigation receivers so I don't think it is a problem on the airplanes. I know that it happens in the mornings, although recently on an afternoon arrival, the VOR seemed to work normally. This anomaly has caused my aircraft to start to turn in before reaching the pxr 015 degrees radial when using the autoplt VOR/localizer feature to capture the course. If it hadn't been VFR and we weren't familiar with the geographic position of the radial we would have turned to a heading of 195 degrees about 8 mi too soon. Even if the crew doesn't use the VOR/localizer feature of the autoplt or flight director system, having the CDI jump inward could mislead a crew into turning in prior to the actual course. I don't know if this anomaly has caused any traffic problems. I have mentioned it to ZAB and phoenix TRACON, and they don't seem to have had any other comments about it. The initial CDI movements are erratic so most pilots probably recognize that the needle movements are erroneous. However, as I mentioned before, if the crew uses the autoplt VOR/localizer feature to capture the pxr 015 degree radial the aircraft will start to turn to a heading of 195 degrees too soon.

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Original NASA ASRS Text

Title: ATC NAV AID PROB ERRATIC VOR.

Narrative: FOR ABOUT 8 MONTHS I HAVE NOTICED THAT PHOENIX VOR HAS HAD AN ANOMALY IN THE NE QUADRANT. COMING IN ON THE FOSSL 2 ARR, THE COURSE DEV INDICATORS FOR BOTH NAV RECEIVERS HAVE FLUCTUATED PLUS OR MINUS 5 DEGS. THIS OCCURS FROM 30-60 NM OUT AND FROM FL250 AND BELOW. THIS HAS HAPPENED IN DIFFERENT ACFT AND TO BOTH NAV RECEIVERS SO I DON'T THINK IT IS A PROB ON THE AIRPLANES. I KNOW THAT IT HAPPENS IN THE MORNINGS, ALTHOUGH RECENTLY ON AN AFTERNOON ARR, THE VOR SEEMED TO WORK NORMALLY. THIS ANOMALY HAS CAUSED MY ACFT TO START TO TURN IN BEFORE REACHING THE PXR 015 DEGS RADIAL WHEN USING THE AUTOPLT VOR/LOC FEATURE TO CAPTURE THE COURSE. IF IT HADN'T BEEN VFR AND WE WEREN'T FAMILIAR WITH THE GEOGRAPHIC POS OF THE RADIAL WE WOULD HAVE TURNED TO A HEADING OF 195 DEGS ABOUT 8 MI TOO SOON. EVEN IF THE CREW DOESN'T USE THE VOR/LOC FEATURE OF THE AUTOPLT OR FLT DIRECTOR SYS, HAVING THE CDI JUMP INWARD COULD MISLEAD A CREW INTO TURNING IN PRIOR TO THE ACTUAL COURSE. I DON'T KNOW IF THIS ANOMALY HAS CAUSED ANY TFC PROBS. I HAVE MENTIONED IT TO ZAB AND PHOENIX TRACON, AND THEY DON'T SEEM TO HAVE HAD ANY OTHER COMMENTS ABOUT IT. THE INITIAL CDI MOVEMENTS ARE ERRATIC SO MOST PLTS PROBABLY RECOGNIZE THAT THE NEEDLE MOVEMENTS ARE ERRONEOUS. HOWEVER, AS I MENTIONED BEFORE, IF THE CREW USES THE AUTOPLT VOR/LOC FEATURE TO CAPTURE THE PXR 015 DEG RADIAL THE ACFT WILL START TO TURN TO A HDG OF 195 DEGS TOO SOON.

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.