Narrative:

While at cruise flight at FL380; a very small; non-identified yaw moment was felt. The first officer did not feel it; but I did. However; I could not rule out just some turbulence. About 10 minutes later; a more significant yaw moment was felt by both of us. I turned to the flight control page; but noted no irregularities. No EICAS messages. Within two to three minutes; we began to experience a series of what felt to be rudder deflections. No EICAS messages; rudder movement on the flight control page were approximately 5 to 10% deflection within the limiter; and the slip indicator was nearly full deflection outside the sky pointer. The aircraft felt as if dutch roll was imminent; however; the yaw dampers recovered. This proceeded to continue. The first officer and I discussed the possible responses while observing the flight control page. I quickly checked the QRH for any procedure that may have been related to our issue; but did not identify a procedure that would apply. We decided that the safest thing was to divert. An ACARS was sent to dispatch of our possible diversion and suggested a nearby airport. We communicated with ATC requesting lower. We informed them that [we] were working through something and might need to divert. I communicated with the lead flight attendant of what were experiencing and our probable diversion.during the descent; the deflection of the rudder continued; so we informed ATC that we would be diverting. We declared an emergency due to flight control irregularity and requested crash fire rescue equipment. I informed the lead flight attendant of our status; precautionary landing; 15 minutes; no need to brace. I then made an announcement to the passengers. The arrival was uneventful; other than continued; however; lessened rudder deflection. Operations acquired a new aircraft; and the flight resumed with all passengers about 4 hours later. I am unaware of why we had rudder deflection. Possibilities range from yaw damper malfunction; but there were no EICAS messages to suggest this. Other possibilities included rudder damage or malfunction; which is why we diverted.

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Original NASA ASRS Text

Title: A CRJ-900 flight crew declared an emergency and diverted to a nearby airport due to repeated uncommanded rudder deflections.

Narrative: While at cruise flight at FL380; a very small; non-identified yaw moment was felt. The First Officer did not feel it; but I did. However; I could not rule out just some turbulence. About 10 minutes later; a more significant yaw moment was felt by both of us. I turned to the flight control page; but noted no irregularities. No EICAS messages. Within two to three minutes; we began to experience a series of what felt to be rudder deflections. No EICAS messages; rudder movement on the flight control page were approximately 5 to 10% deflection within the limiter; and the slip indicator was nearly full deflection outside the sky pointer. The aircraft felt as if Dutch Roll was imminent; however; the yaw dampers recovered. This proceeded to continue. The First Officer and I discussed the possible responses while observing the flight control page. I quickly checked the QRH for any procedure that may have been related to our issue; but did not identify a procedure that would apply. We decided that the safest thing was to divert. An ACARS was sent to Dispatch of our possible diversion and suggested a nearby airport. We communicated with ATC requesting lower. We informed them that [we] were working through something and might need to divert. I communicated with the lead Flight Attendant of what were experiencing and our probable diversion.During the descent; the deflection of the rudder continued; so we informed ATC that we would be diverting. We declared an emergency due to flight control irregularity and requested CFR. I informed the lead Flight Attendant of our status; precautionary landing; 15 minutes; no need to brace. I then made an announcement to the passengers. The arrival was uneventful; other than continued; however; lessened rudder deflection. Operations acquired a new aircraft; and the flight resumed with all passengers about 4 hours later. I am unaware of why we had rudder deflection. Possibilities range from YAW Damper malfunction; but there were no EICAS messages to suggest this. Other possibilities included rudder damage or malfunction; which is why we diverted.

Data retrieved from NASA's ASRS site as of July 2013 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.