Air carrier has autoflt try to turn off arrival course. Reset a different mode and all is well.

Attributes
ACN	453590
Time
Date	199910
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : spane
State Reference	UT
Altitude	msl single value : 19000
Aircraft 1
Controlling Facilities	tracon : s56.tracon
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival star : spane 2
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp
ASRS Report	453590
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

SPANE2 arrival into slc. Navigation track mode with raw data backup. Aircraft started a right turn 90 degrees off arrival track at spane intersection. Went to heading select to correct.

Original NASA ASRS Text

Title: ACR HAS AUTOFLT TRY TO TURN OFF ARR COURSE. RESET A DIFFERENT MODE AND ALL IS WELL.

Narrative: SPANE2 ARR INTO SLC. NAV TRACK MODE WITH RAW DATA BACKUP. ACFT STARTED A R TURN 90 DEGS OFF ARR TRACK AT SPANE INTXN. WENT TO HEADING SELECT TO CORRECT.

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.