Narrative:

Cleared for approach for ILS xxl. Aircraft on autopilot; ILS armed. Joined localizer properly outside of intersection; about 18 miles final. Aircraft then began to drift off of localizer center almost one dot to right of course. This was drifting toward parallel traffic and did not seem to be correcting. Pilot flying used tcs (touch control steering) to reposition aircraft on localizer with needle centered and then allowed autopilot to have control again. For second time aircraft drifts off center; to left of course this time to almost one dot and again control taken with tcs. After third time went back to the right again pilot flying disengaged autopilot and hand flew to about 1000 ft AGL at which point autopilot was re-engaged and was successfully flown for rest of approach and landing. Flight director was on during entire approach. Good CRM was used between captain (pilot flying) and first officer (pilot not flying) to maintain situational awareness and avoid potential traffic conflict as well as to avoid possible go-around. Not sure; I have seen this four other times on various runways; but this is the worst I have seen a captured localizer drift off. I have heard that this has been a problem on the E190; but do not know the cause or a fix for it other than to turn off the automation and hand fly until closer. From what I have heard and seen this has been an occasional problem when turned onto a localizer on a long final. It does not seem to occur on shorter finals in the same way and it does seem to finally correct once on short final. Put out a bulletin describing this problem and how the E190 training department suggests to best deal with a drifting localizer when captured on ILS. If there are any temporary fixes or work arounds I would suggest using them until embraer can implement a full fix. This is enough drift that without pilot intervention we would have exceeded ILS tolerances and possibly conflicted with parallel traffic. I consider this a navigational error with the E190 automation that should be looked into.callback conversation with reporter revealed the following information: reporter advised the flight director command bars were not commanding a return to course either. He felt this implies that the failure mode affects the entire auto flight system and is not indicative of a simple auto pilot anomaly. He also advised the aircraft does have a navigation mode annunciator system (the precise name of which he had forgotten) and that it did indicate a localizer capture in every instance. Unfortunately; he was not aware of the equipment manufacturer.

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Original NASA ASRS Text

Title: Embraer 190 Captain experienced repeated failures of autopilot to track the localizer when on a long final.

Narrative: Cleared for approach for ILS XXL. Aircraft on autopilot; ILS armed. Joined localizer properly outside of intersection; about 18 miles final. Aircraft then began to drift off of localizer center almost one dot to right of course. This was drifting toward parallel traffic and did not seem to be correcting. Pilot flying used TCS (Touch Control Steering) to reposition aircraft on localizer with needle centered and then allowed autopilot to have control again. For second time aircraft drifts off center; to left of course this time to almost one dot and again control taken with TCS. After third time went back to the right again pilot flying disengaged autopilot and hand flew to about 1000 FT AGL at which point autopilot was re-engaged and was successfully flown for rest of approach and landing. Flight Director was on during entire approach. Good CRM was used between Captain (pilot flying) and First Officer (pilot not flying) to maintain situational awareness and avoid potential traffic conflict as well as to avoid possible go-around. Not sure; I have seen this four other times on various runways; but this is the worst I have seen a captured localizer drift off. I have heard that this has been a problem on the E190; but do not know the cause or a fix for it other than to turn off the automation and hand fly until closer. From what I have heard and seen this has been an occasional problem when turned onto a localizer on a long final. It does not seem to occur on shorter finals in the same way and it does seem to finally correct once on short final. Put out a bulletin describing this problem and how the E190 Training Department suggests to best deal with a drifting localizer when captured on ILS. If there are any temporary fixes or work arounds I would suggest using them until Embraer can implement a full fix. This is enough drift that without pilot intervention we would have exceeded ILS tolerances and possibly conflicted with parallel traffic. I consider this a navigational error with the E190 automation that should be looked into.Callback conversation with reporter revealed the following information: Reporter advised the Flight Director command bars were not commanding a return to course either. He felt this implies that the failure mode affects the entire auto flight system and is not indicative of a simple auto pilot anomaly. He also advised the aircraft does have a navigation mode annunciator system (the precise name of which he had forgotten) and that it did indicate a localizer capture in every instance. Unfortunately; he was not aware of the equipment manufacturer.

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.