Unexplained localizer needle deviation on final approach.

Attributes
ACN	284305
Time
Date	199409
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sfo
State Reference	CA
Altitude	msl bound lower : 3700 msl bound upper : 3700
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 13000 flight time type : 2000
ASRS Report	284305
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

On approach to runway 28R sfo, about 7 mi final, the #2 autoplt captured the localizer and started to track it. Then the localizer needle went hard to the right as if the localizer failed, no flags. We corrected to the right, but could not get localizer to come back. Approach turned us to the left, and localizer centered -- we were back on course, instruments checked ok (with ATC concurrence) and we landed without incident. We wrote up the compass system.

Original NASA ASRS Text

Title: UNEXPLAINED LOC NEEDLE DEV ON FINAL APCH.

Narrative: ON APCH TO RWY 28R SFO, ABOUT 7 MI FINAL, THE #2 AUTOPLT CAPTURED THE LOC AND STARTED TO TRACK IT. THEN THE LOC NEEDLE WENT HARD TO THE R AS IF THE LOC FAILED, NO FLAGS. WE CORRECTED TO THE R, BUT COULD NOT GET LOC TO COME BACK. APCH TURNED US TO THE L, AND LOC CTRED -- WE WERE BACK ON COURSE, INSTS CHKED OK (WITH ATC CONCURRENCE) AND WE LANDED WITHOUT INCIDENT. WE WROTE UP THE COMPASS SYS.

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.