Aircraft navigation system became unreliable. Flight crew diverts to VFR airport.

Attributes
ACN	546263
Time
Date	200205
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : fmn.vortac
State Reference	NM
Altitude	msl single value : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other Other
Flight Phase	cruise : level
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 6500 flight time type : 1700
ASRS Report	546263
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other controllerb
Resolutory Action	controller : provided flight assist controller : issued new clearance controller : issued advisory flight crew : diverted to another airport
Consequence	faa : reviewed incident with flight crew other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance Weather
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Somewhere east of lvs, we were cleared to fly direct RNAV to ilc. Our FMS had been accurate up to around fmn. About 100-150 DME west of fmn, center called to ask if we were still on an assigned heading. I replied that we were not on a heading, but flying direct to ilc. We were then told we were off course and to turn 20 degrees right. We complied and began to check the status of our FMS. The 'verify position' message appeared and it became evident that the FMS had lost its alignment. The automatic window of the VOR flashed 108.0, meaning it could not find a station from which to get a fix. We were given a turn another 15 degrees right. We consulted our new operations manuals. The QRH had no procedure. The operations manual, volume 2, had a brief description of what to do for a loss of alignment. It involved selecting 'att' mode on the IRS panel and entering heading manually. After another 40 degree turn to the right, the copilot stated that the heading was 'way off.' it appeared to me that he was right. We discussed selecting 'att.' we selected 'att' on the IRS and promptly lost the autoplt and the RDMI and HSI. The copilot then manually flew and talked on the radio while I contacted the dispatcher. The duty pilot was not available, so we talked with the maintenance coordinator. He suggested pulling and resetting several circuit breakers. We did this and temporarily lost the ADI. When I got the ADI back, I discontinued the 'help' of maintenance. Our destination, oak, was IFR, so I requested a divert to a VMC field and vectors to remain in VMC to landing. This was granted and we landed in slc uneventfully. Conclusions: the training on the IRS and the FMS is very limited and usually only done at the initial school. We just converted to new manuals and have not yet been fully trained in their use. As captain, I could have taken more time to assess the situation before acting. The decision to divert to a VFR field I felt was a good one.

Original NASA ASRS Text

Title: ACFT NAV SYS BECAME UNRELIABLE. FLC DIVERTS TO VFR ARPT.

Narrative: SOMEWHERE E OF LVS, WE WERE CLRED TO FLY DIRECT RNAV TO ILC. OUR FMS HAD BEEN ACCURATE UP TO AROUND FMN. ABOUT 100-150 DME W OF FMN, CTR CALLED TO ASK IF WE WERE STILL ON AN ASSIGNED HDG. I REPLIED THAT WE WERE NOT ON A HDG, BUT FLYING DIRECT TO ILC. WE WERE THEN TOLD WE WERE OFF COURSE AND TO TURN 20 DEGS R. WE COMPLIED AND BEGAN TO CHK THE STATUS OF OUR FMS. THE 'VERIFY POS' MESSAGE APPEARED AND IT BECAME EVIDENT THAT THE FMS HAD LOST ITS ALIGNMENT. THE AUTO WINDOW OF THE VOR FLASHED 108.0, MEANING IT COULD NOT FIND A STATION FROM WHICH TO GET A FIX. WE WERE GIVEN A TURN ANOTHER 15 DEGS R. WE CONSULTED OUR NEW OPS MANUALS. THE QRH HAD NO PROC. THE OPS MANUAL, VOLUME 2, HAD A BRIEF DESCRIPTION OF WHAT TO DO FOR A LOSS OF ALIGNMENT. IT INVOLVED SELECTING 'ATT' MODE ON THE IRS PANEL AND ENTERING HDG MANUALLY. AFTER ANOTHER 40 DEG TURN TO THE R, THE COPLT STATED THAT THE HDG WAS 'WAY OFF.' IT APPEARED TO ME THAT HE WAS RIGHT. WE DISCUSSED SELECTING 'ATT.' WE SELECTED 'ATT' ON THE IRS AND PROMPTLY LOST THE AUTOPLT AND THE RDMI AND HSI. THE COPLT THEN MANUALLY FLEW AND TALKED ON THE RADIO WHILE I CONTACTED THE DISPATCHER. THE DUTY PLT WAS NOT AVAILABLE, SO WE TALKED WITH THE MAINT COORDINATOR. HE SUGGESTED PULLING AND RESETTING SEVERAL CIRCUIT BREAKERS. WE DID THIS AND TEMPORARILY LOST THE ADI. WHEN I GOT THE ADI BACK, I DISCONTINUED THE 'HELP' OF MAINT. OUR DEST, OAK, WAS IFR, SO I REQUESTED A DIVERT TO A VMC FIELD AND VECTORS TO REMAIN IN VMC TO LNDG. THIS WAS GRANTED AND WE LANDED IN SLC UNEVENTFULLY. CONCLUSIONS: THE TRAINING ON THE IRS AND THE FMS IS VERY LIMITED AND USUALLY ONLY DONE AT THE INITIAL SCHOOL. WE JUST CONVERTED TO NEW MANUALS AND HAVE NOT YET BEEN FULLY TRAINED IN THEIR USE. AS CAPT, I COULD HAVE TAKEN MORE TIME TO ASSESS THE SIT BEFORE ACTING. THE DECISION TO DIVERT TO A VFR FIELD I FELT WAS A GOOD ONE.

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.