Reporter was 4 mi off course as viewed by ATC radar and on centerline as viewed by aircraft FMS.

Attributes
ACN	297580
Time
Date	199502
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : csn
State Reference	VA
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 5500 flight time type : 265
ASRS Report	297580
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Center called to tell us we were 3 NM east of J48 into csn, and asked if we were RNAV equipped. We said that we were. Our FMS showed us to be centered on the jet route with no x-track error. The controller gave us a 265 degree heading for a few min, then cleared us direct to csn flight plan route. The captain asked how far we had gotten off course and he said 4 NM. We asked for direct clrncs to mol and odf after that, and wrote up our FMS. No further discussions entailed. Our FMS must have been off.

Original NASA ASRS Text

Title: RPTR WAS 4 MI OFF COURSE AS VIEWED BY ATC RADAR AND ON CTRLINE AS VIEWED BY ACFT FMS.

Narrative: CTR CALLED TO TELL US WE WERE 3 NM E OF J48 INTO CSN, AND ASKED IF WE WERE RNAV EQUIPPED. WE SAID THAT WE WERE. OUR FMS SHOWED US TO BE CTRED ON THE JET RTE WITH NO X-TRACK ERROR. THE CTLR GAVE US A 265 DEG HDG FOR A FEW MIN, THEN CLRED US DIRECT TO CSN FLT PLAN RTE. THE CAPT ASKED HOW FAR WE HAD GOTTEN OFF COURSE AND HE SAID 4 NM. WE ASKED FOR DIRECT CLRNCS TO MOL AND ODF AFTER THAT, AND WROTE UP OUR FMS. NO FURTHER DISCUSSIONS ENTAILED. OUR FMS MUST HAVE BEEN OFF.

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.