Flight crew was flying off course due to FMC equipment problem.

Attributes
ACN	419020
Time
Date	199810
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fnt
State Reference	MI
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp
Experience	flight time last 90 days : 180 flight time total : 4800 flight time type : 2400
ASRS Report	419020
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

ZOB asked us if we were cleared direct pmm or on our flight planned route. I replied flight planned route. After looking at FMC, we realized dewit intersection and possibly fnt dropped out. Never have seen this before. We checked our position with NAVAID and we were 4 NM from centerline.

Original NASA ASRS Text

Title: FLC WAS FLYING OFF COURSE DUE TO FMC EQUIP PROB.

Narrative: ZOB ASKED US IF WE WERE CLRED DIRECT PMM OR ON OUR FLT PLANNED RTE. I REPLIED FLT PLANNED RTE. AFTER LOOKING AT FMC, WE REALIZED DEWIT INTXN AND POSSIBLY FNT DROPPED OUT. NEVER HAVE SEEN THIS BEFORE. WE CHKED OUR POS WITH NAVAID AND WE WERE 4 NM FROM CTRLINE.

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.