Air carrier fails to capture localizer when ILS mode of autoflt is engaged.

Attributes
ACN	779207
Time
Date	200803
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : slc.airport
State Reference	UT
Altitude	msl single value : 11000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : s56.tracon
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 16l
Flight Phase	descent : approach
Route In Use	arrival star : skees
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp pilot : multi engine pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 12000 flight time type : 7000
ASRS Report	779207
Events
Anomaly	aircraft equipment problem : less severe non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	controller : issued advisory flight crew : overrode automation flight crew : diverted to another airport
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

On skees 2 RNAV arrival to slc from the north. At approximately irron intersection while in the navigation mode; we were cleared for the ILS 16L approach. With the raw data for the localizer 16L centered and verified; ILS mode was selected. The aircraft immediately initiated a 30 degree bank r-hand turn uncommanded. As soon as it was recognized that this was not a capture maneuver; the autoplt was disconnected; and a turn back to intercept localizer was initiated. Approximately 45 degrees of heading change occurred. A call was received from approach control while in the turn-back; instructing us to come left to recapture the localizer. No loss of separation is believed to have occurred; and the reason for the uncommanded right turn is unknown to me at this time. In the future; I will be much more wary of transitions from navigation to ILS; and be that much quicker to disconnect the autoplt when observing an unsatisfactory response.

Original NASA ASRS Text

Title: ACR FAILS TO CAPTURE LOCALIZER WHEN ILS MODE OF AUTOFLT IS ENGAGED.

Narrative: ON SKEES 2 RNAV ARR TO SLC FROM THE N. AT APPROX IRRON INTXN WHILE IN THE NAV MODE; WE WERE CLRED FOR THE ILS 16L APCH. WITH THE RAW DATA FOR THE LOC 16L CTRED AND VERIFIED; ILS MODE WAS SELECTED. THE ACFT IMMEDIATELY INITIATED A 30 DEG BANK R-HAND TURN UNCOMMANDED. AS SOON AS IT WAS RECOGNIZED THAT THIS WAS NOT A CAPTURE MANEUVER; THE AUTOPLT WAS DISCONNECTED; AND A TURN BACK TO INTERCEPT LOC WAS INITIATED. APPROX 45 DEGS OF HDG CHANGE OCCURRED. A CALL WAS RECEIVED FROM APCH CTL WHILE IN THE TURN-BACK; INSTRUCTING US TO COME L TO RECAPTURE THE LOC. NO LOSS OF SEPARATION IS BELIEVED TO HAVE OCCURRED; AND THE REASON FOR THE UNCOMMANDED R TURN IS UNKNOWN TO ME AT THIS TIME. IN THE FUTURE; I WILL BE MUCH MORE WARY OF TRANSITIONS FROM NAV TO ILS; AND BE THAT MUCH QUICKER TO DISCONNECT THE AUTOPLT WHEN OBSERVING AN UNSATISFACTORY RESPONSE.

Data retrieved from NASA's ASRS site as of May 2009 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.