Crj-200 first officer reported that on approach mode the autopilot kept wanting to roll left.

Narrative:

On approach we had been given a left turn to intercept the localizer and we were cleared for the approach. We got an auto pilot trim warning message that had gone away on its own. No pilot action. Approach mode was armed and the auto pilot seemed to join and track the localizer until it did two separate snap rolls of 10 degrees or more to the right which was opposite of the correction needed for the localizer. At that time I disconnected the autopilot and rejoined the localizer. After we rejoined the localizer the airplane kept wanting to roll left even after adding more than half of the available rearward aileron trim. We were now established on the ILS with the airplane still wanting to roll to the left; due to the hard tendency to roll left we had become left of course and unstable. We had reached visual conditions and elected to continue due to it being a possible flight control issue that seemed to be getting worse as we flew. We landed and rolled out without incident. We called and notified maintenance of the discrepancy.autopilot making incorrect and erratic corrections to track the localizer. Night IMC conditions with a trim system that seemed to be fighting our inputs.remember to keep a quick and efficient instrument scan going even when the scan requires you to check other things that you normally wouldn't. Possibly add into preflight or approach briefings what actions you would take if you have a flight control or trim issue just like we brief if we have an engine failure.

Original NASA ASRS Text

Title: CRJ-200 First Officer reported that on approach mode the autopilot kept wanting to roll left.

Narrative: On approach we had been given a left turn to intercept the LOC and we were cleared for the approach. We got an auto pilot trim warning message that had gone away on its own. No pilot action. Approach mode was armed and the auto pilot seemed to join and track the LOC until it did two separate snap rolls of 10 degrees or more to the right which was opposite of the correction needed for the LOC. At that time I disconnected the autopilot and rejoined the LOC. After we rejoined the LOC the airplane kept wanting to roll left even after adding more than half of the available Rearward aileron trim. We were now established on the ILS with the airplane still wanting to roll to the left; due to the hard tendency to roll left we had become left of course and unstable. We had reached visual conditions and elected to continue due to it being a possible flight control issue that seemed to be getting worse as we flew. We landed and rolled out without incident. We called and notified Maintenance of the discrepancy.Autopilot making incorrect and erratic corrections to track the LOC. Night IMC conditions with a trim system that seemed to be fighting our inputs.Remember to keep a quick and efficient instrument scan going even when the scan requires you to check other things that you normally wouldn't. Possibly add into preflight or approach briefings what actions you would take if you have a flight control or trim issue just like we brief if we have an engine failure.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1521557
Time
Date	201802
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.TRACON
State Reference	US
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	Regional Jet 200 ER/LR (CRJ200)
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Inflight Event / Encounter Unstabilized Approach