MD80 flight crew drifted south of ATC's intended course, following the published VOR radial.

Attributes
ACN	495361
Time
Date	200012
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : jct.vortac
State Reference	TX
Altitude	msl single value : 26000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	cruise : level
Route In Use	departure sid : jcti.jct enroute airway : j86.airway
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 220 flight time total : 23000 flight time type : 16000
ASRS Report	495361
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp pilot : cfi
Experience	flight time last 90 days : 240 flight time total : 14000 flight time type : 1400
ASRS Report	495360
Events
Anomaly	non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Aircraft Navigational Facility Flight Crew Human Performance
Primary Problem	Navigational Facility
Air Traffic Incident	Pilot Deviation

Narrative:

We had leveled off at FL260 and were tracking the junction 1 departure as cleared per the pre departure clearance. Shortly after leveloff, both vors showed on course. I had just tuned mine to the junction VOR. I was correcting about 20 degrees to the left to stay on course. Center questioned what we were doing and gave us direct to the centex VOR direct to the san angelo VOR. Perhaps we had some fluctuations of the VOR signal to cause center's concern. It was center, ZHU. The controller commented about a possible equipment problem. On dec/xa/00 we flew the same route with a different aircraft. We noted the junction 090 degree radial showed 1/2 DOT south when tracking out the humble 273 degree radial from 80 mi west of humble to 115 mi west.

Original NASA ASRS Text

Title: MD80 FLC DRIFTED S OF ATC'S INTENDED COURSE, FOLLOWING THE PUBLISHED VOR RADIAL.

Narrative: WE HAD LEVELED OFF AT FL260 AND WERE TRACKING THE JUNCTION 1 DEP AS CLRED PER THE PDC. SHORTLY AFTER LEVELOFF, BOTH VORS SHOWED ON COURSE. I HAD JUST TUNED MINE TO THE JUNCTION VOR. I WAS CORRECTING ABOUT 20 DEGS TO THE L TO STAY ON COURSE. CTR QUESTIONED WHAT WE WERE DOING AND GAVE US DIRECT TO THE CENTEX VOR DIRECT TO THE SAN ANGELO VOR. PERHAPS WE HAD SOME FLUCTUATIONS OF THE VOR SIGNAL TO CAUSE CTR'S CONCERN. IT WAS CENTER, ZHU. THE CTLR COMMENTED ABOUT A POSSIBLE EQUIP PROB. ON DEC/XA/00 WE FLEW THE SAME RTE WITH A DIFFERENT ACFT. WE NOTED THE JUNCTION 090 DEG RADIAL SHOWED 1/2 DOT S WHEN TRACKING OUT THE HUMBLE 273 DEG RADIAL FROM 80 MI W OF HUMBLE TO 115 MI W.

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.