B737-300. ZAB controller notes that the aircraft was not proceeding to the cleared VOR.

Attributes
ACN	546070
Time
Date	200205
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : fmn.airport
State Reference	NM
Altitude	msl single value : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 5500 flight time type : 3700
ASRS Report	546070
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance other anomaly other other spatial deviation
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : issued alert controller : issued new clearance controller : provided flight assist flight crew : diverted to another airport flight crew : landed as precaution none taken : detected after the fact other
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

During flight to oak, the captain and I were flying at FL350 when center called and asked if we were still on a heading or cleared direct to ilc. The captain responded that we were proceeding direct to ilc. I immediately checked our navigation to confirm that ilc was still shown direct in the FMS and that LNAV was selected. Center informed us that we needed to turn right 20 degrees to proceed direct. At that time I selected ilc once again to proceed direct. Prior to the selection of direct ilc, our HSI showed us direct. Upon selecting direct once again, there was no change in heading and no change in course. I began a right hand turn using heading sel to proceed in the direction that center had stated, while we began to look at our situation. Neither autoplt corrected the heading problem and we concluded we had an IRS/FMS problem. The captain pulled out the QRH. The QRH did not lead to a solution. About this time center called us and stated that we needed to come an additional 10 degrees right. He responded that we were possibly having a navigation problem, while I dialed in an additional 10 degrees right. The captain referred to the aircraft manual without success. Once again center called with an additional heading change, which I complied with. It appeared that our heading system was either completely off or drifting slowly. I proceeded to hand fly the aircraft as neither autoplt would engage. I took over the radios and continued to fly as the captain contacted the duty pilot. While the captain worked the problem through company radio, I kept center informed of our situation and requested a block altitude of FL350-FL370. Company maintenance was not able to supply any additional information on the problem, so at this time the captain decided that we needed to stay VMC and through coordination with the dispatcher, slc was determined to be our best divert. WX at oak was 1100 ft overcast. The captain then resumed control of the radios and requested that we wanted to remain VMC to the field. ATC complied and stated that we could deviate as necessary to stay VMC. We proceeded to slc and landed uneventfully. Maintenance met the captain at the gate, and after a few mins, we were informed that slc had a spare aircraft for us to continue to oak.

Original NASA ASRS Text

Title: B737-300. ZAB CTLR NOTES THAT THE ACFT WAS NOT PROCEEDING TO THE CLRED VOR.

Narrative: DURING FLT TO OAK, THE CAPT AND I WERE FLYING AT FL350 WHEN CTR CALLED AND ASKED IF WE WERE STILL ON A HEADING OR CLRED DIRECT TO ILC. THE CAPT RESPONDED THAT WE WERE PROCEEDING DIRECT TO ILC. I IMMEDIATELY CHKED OUR NAV TO CONFIRM THAT ILC WAS STILL SHOWN DIRECT IN THE FMS AND THAT LNAV WAS SELECTED. CTR INFORMED US THAT WE NEEDED TO TURN R 20 DEGS TO PROCEED DIRECT. AT THAT TIME I SELECTED ILC ONCE AGAIN TO PROCEED DIRECT. PRIOR TO THE SELECTION OF DIRECT ILC, OUR HSI SHOWED US DIRECT. UPON SELECTING DIRECT ONCE AGAIN, THERE WAS NO CHANGE IN HEADING AND NO CHANGE IN COURSE. I BEGAN A R HAND TURN USING HEADING SEL TO PROCEED IN THE DIRECTION THAT CTR HAD STATED, WHILE WE BEGAN TO LOOK AT OUR SIT. NEITHER AUTOPLT CORRECTED THE HEADING PROB AND WE CONCLUDED WE HAD AN IRS/FMS PROB. THE CAPT PULLED OUT THE QRH. THE QRH DID NOT LEAD TO A SOLUTION. ABOUT THIS TIME CTR CALLED US AND STATED THAT WE NEEDED TO COME AN ADDITIONAL 10 DEGS R. HE RESPONDED THAT WE WERE POSSIBLY HAVING A NAV PROB, WHILE I DIALED IN AN ADDITIONAL 10 DEGS R. THE CAPT REFERRED TO THE ACFT MANUAL WITHOUT SUCCESS. ONCE AGAIN CTR CALLED WITH AN ADDITIONAL HEADING CHANGE, WHICH I COMPLIED WITH. IT APPEARED THAT OUR HEADING SYS WAS EITHER COMPLETELY OFF OR DRIFTING SLOWLY. I PROCEEDED TO HAND FLY THE ACFT AS NEITHER AUTOPLT WOULD ENGAGE. I TOOK OVER THE RADIOS AND CONTINUED TO FLY AS THE CAPT CONTACTED THE DUTY PLT. WHILE THE CAPT WORKED THE PROB THROUGH COMPANY RADIO, I KEPT CTR INFORMED OF OUR SIT AND REQUESTED A BLOCK ALT OF FL350-FL370. COMPANY MAINT WAS NOT ABLE TO SUPPLY ANY ADDITIONAL INFO ON THE PROB, SO AT THIS TIME THE CAPT DECIDED THAT WE NEEDED TO STAY VMC AND THROUGH COORD WITH THE DISPATCHER, SLC WAS DETERMINED TO BE OUR BEST DIVERT. WX AT OAK WAS 1100 FT OVCST. THE CAPT THEN RESUMED CTL OF THE RADIOS AND REQUESTED THAT WE WANTED TO REMAIN VMC TO THE FIELD. ATC COMPLIED AND STATED THAT WE COULD DEVIATE AS NECESSARY TO STAY VMC. WE PROCEEDED TO SLC AND LANDED UNEVENTFULLY. MAINT MET THE CAPT AT THE GATE, AND AFTER A FEW MINS, WE WERE INFORMED THAT SLC HAD A SPARE ACFT FOR US TO CONTINUE TO OAK.

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.