An air carrier pilot reports the stx VOR bearing signals are unreliable and fluctuate excessively.

Attributes
ACN	755141
Time
Date	200709
Place
Locale Reference	navaid : coy.vor
State Reference	VI
Altitude	msl single value : 7000
Aircraft 1
Controlling Facilities	artcc : zsu.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	cruise : enroute altitude change
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial
ASRS Report	755141
Events
Anomaly	other spatial deviation
Resolutory Action	flight crew : returned to intended or assigned course
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Navigational Facility
Primary Problem	Navigational Facility
Situations
Navigational Aid	COY.VOR

Narrative:

Cleared direct st croix VOR -- 76 NM (7000 ft cruise) 134 radial inbound; needle initially centered. Proceeded to go full scale left (north) of course. After a few seconds went full scale to 1 DOT right (south) of course. Approximately 60 miles from VOR stayed within 1/4 DOT -- 1 full DOT deviations then centered. Continued minor deviations (1/2 DOT to 1 DOT) until approach into stx. We asked ATC to verify our position (direct stx). Our heading was correct but the CDI wasn't centered. It was 1/2 DOT off to the south. St croix VOR is very unreliable at any distance.

Original NASA ASRS Text

Title: AN ACR PILOT REPORTS THE STX VOR BEARING SIGNALS ARE UNRELIABLE AND FLUCTUATE EXCESSIVELY.

Narrative: CLRED DIRECT ST CROIX VOR -- 76 NM (7000 FT CRUISE) 134 RADIAL INBOUND; NEEDLE INITIALLY CENTERED. PROCEEDED TO GO FULL SCALE LEFT (NORTH) OF COURSE. AFTER A FEW SECONDS WENT FULL SCALE TO 1 DOT RIGHT (SOUTH) OF COURSE. APPROX 60 MILES FROM VOR STAYED WITHIN 1/4 DOT -- 1 FULL DOT DEVIATIONS THEN CENTERED. CONTINUED MINOR DEVIATIONS (1/2 DOT TO 1 DOT) UNTIL APCH INTO STX. WE ASKED ATC TO VERIFY OUR POSITION (DIRECT STX). OUR HDG WAS CORRECT BUT THE CDI WASN'T CENTERED. IT WAS 1/2 DOT OFF TO THE SOUTH. ST CROIX VOR IS VERY UNRELIABLE AT ANY DISTANCE.

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.