Narrative:

Approach cleared us to intercept the localizer runway xxr. Navigation was selected (in green needles) and the localizer captured. The autopilot deviated .25 NM left of the localizer and began a very slow turn back to the right. ATC asked if we were intercepting the localizer to runway xxr and we answered that we were. There was never any conflict with other traffic. We were cleared for the approach and the approach mode was selected. The autopilot then deviated nearly 1 dot right of course (outside of the FAF). I manually took control of the airplane and manually flew the aircraft for the rest of the approach and landing. During the final approach; FAF inbound; the FD was giving good information and the localizer and GS were tracking without error. The approach mode of the autopilot worked flawlessly on the previous flight and also on the next 2 legs. It is not known if the localizer deviations were the result of an anomaly in the airplane or with the localizer equipment on the ground.

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Original NASA ASRS Text

Title: E190 Captain reports the autopilot deviated substantially from the localizer after capture.

Narrative: Approach cleared us to intercept the LOC Runway XXR. Navigation was selected (in green needles) and the LOC captured. The autopilot deviated .25 NM left of the LOC and began a very slow turn back to the right. ATC asked if we were intercepting the LOC to Runway XXR and we answered that we were. There was never any conflict with other traffic. We were cleared for the approach and the approach mode was selected. The autopilot then deviated nearly 1 dot right of course (outside of the FAF). I manually took control of the airplane and manually flew the aircraft for the rest of the approach and landing. During the final approach; FAF inbound; the FD was giving good information and the LOC and GS were tracking without error. The approach mode of the autopilot worked flawlessly on the previous flight and also on the next 2 legs. It is not known if the LOC deviations were the result of an anomaly in the airplane or with the LOC equipment on the ground.

Data retrieved from NASA's ASRS site as of April 2012 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.