Date: 201308
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Dawn
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Cruise
Aircraft component: Autoflight Yaw Damper
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Human factors: Troubleshooting
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: At cruise FL310; about 5 minutes into leveling out; I noticed an abrupt yawing motion. I initially thought that the Captain had bumped the rudder pedal. I looked over at him and his feet were not near the pedals. I asked him if he felt that and he said 'Yes'. It was not turbulence; as it was a smooth altitude and didn't feel like turbulence. After another minute or two it happened again; in both directions. I then decided to disconnect the autopilot and hand fly it to make sure it wasn't the automation. As I was hand flying and my feet resting on the rudder pedals it happened again in both directions. I then reconnected the autopilot and every 2-3 minutes we'd get that same uncommanded yaw. The rudder pedals would move along with the direction of yaw as though someone was pushing on them. It created very obvious yaw motion with a few degree nose left/right each time. It created an unstable and undesirable flight path. About seven minutes after we noticed the issue; we asked for lower and descended to FL270. As it kept happening in small intervals we slowed down to Vma. We had no guidance from the QRH; or any other books; so we decided to divert. We were about 40 miles away when we decided to divert. We were cleared direct to the airport and made a left turn; descended and landed uneventfully. The rudder kept kicking left and right during the descent. Upon landing the Yaw Damper-1 (YD-1) Status message illuminated. We found out later the Yaw Damper-1 was faulty. We were nervous the rudder movement was going to get worse and we didn't want any type of full rudder deflection so that's why we decided to divert. I had never experienced this before in the past 5.5 years as a First Officer and the Captain was green with high minimums; so we took the precaution. Mechanical issue...no suggestions except create a checklist for 'Uncommanded Rudder Movement.'


Second narrative: The yaw movements appeared to come from rouge rudder movements; rudder deflection remained minimal (referencing the Flight Control page on the EICAS). Troubleshooting a vital control component with Maintenance was not considered a safe alternative; instead we decided that an expeditious landing was the safest course while the aircraft was in our complete control. No EICAS message appeared in flight. 'YD 1 INOP' status message was noticed on roll-out after landing on [Runway] XR; and remained on into the gate. The AP was disengaged in-flight in an attempt to isolate the rudder deflection; the rudder continued to deflect. The rudder remained responsive to our control inputs throughout the flight. The landing occurred under the aircraft's Max Landing Weight.


Synopsis: A flight crew reported they experienced abrupt yawing motions in a CRJ-200 aircraft that created an unstable flight path.  The First Officer noted the rudder pedals would move along with the direction of yaw as though someone was pushing on them. Rudder continued to kick left and right during descent. No QRH procedure available for uncommanded rudder movement.