Air carrier reporter shows on airway while ARTCC radar indicates off course.

Attributes
ACN	172386
Time
Date	199103
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bal
State Reference	MA
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : alb
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute airway : j518
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 10000 flight time type : 180
ASRS Report	172386
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

I was working with center on 134.15 on J518 midway between baltimore and indian head. I overheard ATC direct the aircraft ahead of us to turn right and get back on J518. He responded that he would turn right, but that he was showing on J518. That caused us to check our position on J518 and it looked good. Shortly after we were directed to turn 30 degrees right and get on J518. We too showed centerline on the arwy. We did as requested and asked the controller to advise us when we showed on J518 to them. They indicated that we were centered on J518 when we showed 3 degrees right (north of course). I checked our navigation radios on the ground with the vot at minneapolis, mn, and all seemed normal. I don't know if the arwy shows different to the controllers or if the changeover point 114 mi from baltimore or 20 mi from indian head causes a problem. Baltimore dots start to fluctuate, but the NAVAID change takes place only 20 mi from indian head. Perhaps this could be checked out.

Original NASA ASRS Text

Title: ACR REPORTER SHOWS ON AIRWAY WHILE ARTCC RADAR INDICATES OFF COURSE.

Narrative: I WAS WORKING WITH CENTER ON 134.15 ON J518 MIDWAY BTWN BALTIMORE AND INDIAN HEAD. I OVERHEARD ATC DIRECT THE ACFT AHEAD OF US TO TURN RIGHT AND GET BACK ON J518. HE RESPONDED THAT HE WOULD TURN RIGHT, BUT THAT HE WAS SHOWING ON J518. THAT CAUSED US TO CHK OUR POS ON J518 AND IT LOOKED GOOD. SHORTLY AFTER WE WERE DIRECTED TO TURN 30 DEGS RIGHT AND GET ON J518. WE TOO SHOWED CENTERLINE ON THE ARWY. WE DID AS REQUESTED AND ASKED THE CTLR TO ADVISE US WHEN WE SHOWED ON J518 TO THEM. THEY INDICATED THAT WE WERE CENTERED ON J518 WHEN WE SHOWED 3 DEGS RIGHT (N OF COURSE). I CHKED OUR NAV RADIOS ON THE GND WITH THE VOT AT MINNEAPOLIS, MN, AND ALL SEEMED NORMAL. I DON'T KNOW IF THE ARWY SHOWS DIFFERENT TO THE CTLRS OR IF THE CHANGEOVER POINT 114 MI FROM BALTIMORE OR 20 MI FROM INDIAN HEAD CAUSES A PROB. BALTIMORE DOTS START TO FLUCTUATE, BUT THE NAVAID CHANGE TAKES PLACE ONLY 20 MI FROM INDIAN HEAD. PERHAPS THIS COULD BE CHKED OUT.

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.