Narrative:

While in cruise at FL260; with the autopilot engaged; we felt a sudden jolt and a very noticeable yaw back and forth. As the pilot flying I took a tighter hold of the control yoke and we both started looking at all the indicators to try to see what had been the cause; including checking if there was any nearby traffic above us that might have been the cause of a wake turbulence encounter.there were no obvious abnormalities; no warning lights or indications.we started to feel the additional yaw excursions. One of us selected the flight cntrl page on the EICAS; and we could then see fairly significant movement of the rudder (not extreme excursions; but more than would normally be seen in cruise).I called for the QRH for un-commanded rudder movement. We ran through the steps; including disconnecting the autopilot and yaw dampers. As soon as the yds (yaw dampers) were disconnected the un-commanded movements stopped.as the conditions did not persist; we were not required to land at the nearest suitable airport. As the aircraft was controllable we decided it was acceptable to continue on. However; as we were worried that the problem could reoccur I determined the safest course of action was to inform ATC so that if we needed to divert everything would be in place for us.we asked for and received a new clearance for lower and slower; and ATC also gave us direct to [the destination]. We were asked for and provided the usual information (souls on board; fuel; etc) as well as a basic description of the problem.we also contacted dispatch and maintenance via ACARS; advising them of the problem; our current condition; and intention to land if nothing further happened; or divert if necessary.lastly; we advised the flight attendants what was happening; that we expected a normal landing and taxi-in; but to be prepared in case the situation worsened and called for a change in plans.we continued the flight; with me flying manually. We asked for and received clearances to allow for relatively gentle descents and turns and a long final so as to keep stresses on the controls light.I performed a normal visual; backed up with the ILS; to the longest runway; followed by a normal touchdown and roll-out.normal taxi-in and parking; after which I contacted [maintenance operations] via telephone to discuss what had happened and the write-up entry I was doing.it appeared to me to be just and odd equipment abnormality. We did discuss the local weather (was it a wind shear issue; etc); but all the weather was far west of our position when it was happening; so that was ruled out as a factor. As I stated above; we thought about a wake turbulence issue; but there was no traffic anywhere near us. And as soon as the yaw dampeners were disconnected the problem seemed to stop.I will also add that it required considerable right rudder trim to center the brick once I started manually flying. Somewhere in the 30-40% range of the indicated available travel. This might or might not be a symptom of the issue.

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Original NASA ASRS Text

Title: CRJ-900 Captain reported that they disconnected the autopilot and yaw dampeners and flew the aircraft manually due to uncommanded rudder movements.

Narrative: While in cruise at FL260; with the autopilot engaged; we felt a sudden jolt and a very noticeable yaw back and forth. As the pilot flying I took a tighter hold of the control yoke and we both started looking at all the indicators to try to see what had been the cause; including checking if there was any nearby traffic above us that might have been the cause of a wake turbulence encounter.There were no obvious abnormalities; no warning lights or indications.We started to feel the additional yaw excursions. One of us selected the FLT CNTRL page on the EICAS; and we could then see fairly significant movement of the rudder (not extreme excursions; but more than would normally be seen in cruise).I called for the QRH for un-commanded rudder movement. We ran through the steps; including disconnecting the autopilot and yaw dampers. As soon as the YDs (Yaw Dampers) were disconnected the un-commanded movements stopped.As the conditions did NOT persist; we were not required to land at the nearest suitable airport. As the aircraft was controllable we decided it was acceptable to continue on. However; as we were worried that the problem could reoccur I determined the safest course of action was to inform ATC so that if we needed to divert everything would be in place for us.We asked for and received a new clearance for lower and slower; and ATC also gave us direct to [the destination]. We were asked for and provided the usual information (souls on board; fuel; etc) as well as a basic description of the problem.We also contacted Dispatch and Maintenance via ACARS; advising them of the problem; our current condition; and intention to land if nothing further happened; or divert if necessary.Lastly; we advised the Flight Attendants what was happening; that we expected a normal landing and taxi-in; but to be prepared in case the situation worsened and called for a change in plans.We continued the flight; with me flying manually. We asked for and received clearances to allow for relatively gentle descents and turns and a long final so as to keep stresses on the controls light.I performed a normal visual; backed up with the ILS; to the longest runway; followed by a normal touchdown and roll-out.Normal taxi-in and parking; after which I contacted [maintenance operations] via telephone to discuss what had happened and the write-up entry I was doing.It appeared to me to be just and odd equipment abnormality. We did discuss the local weather (was it a wind shear issue; etc); but all the weather was far west of our position when it was happening; so that was ruled out as a factor. As I stated above; we thought about a wake turbulence issue; but there was no traffic anywhere near us. And as soon as the Yaw Dampeners were disconnected the problem seemed to stop.I will also add that it required considerable right rudder trim to center the brick once I started manually flying. Somewhere in the 30-40% range of the indicated available travel. This might or might not be a symptom of the issue.

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.