Narrative:

How should a flight crew respond when their aircraft suddenly exhibits apparent flight control malfunctions which don't have a corresponding QRH procedure? Here is how we handled the situation when it happened to us: the flight crew consisted of [our] captain; flight attendant and I; as first officer. During that flight I was pilot flying; and while enroute at FL300 with autopilot engaged; the aircraft suddenly and abruptly yawed first in one direction; then the other; followed by EICAS displaying a yaw damper-1 (yd-1) inoperative status message. We attempted to reset yd-1; but within moments yd-1 disengaged itself again; with another significant lateral movement of the aircraft and corresponding deviation of the EFIS 'brick'. Moments prior to yd-1 disengaging a mechanical 'shudder' was felt in both rudder pedals.there is no specific QRH procedure for operating with one yaw damper inoperative; so we referenced QRH 'yaw damper caution message' in case we lost the other yaw damper; kept yd-1 off; continued to destination and landed there. Contract maintenance came out; and after troubleshooting it was decided that the aircraft should be ferried under special flight permit with yd-1 disengaged. As yd-1 was to remain disengaged; we briefed the departure at the gate to include possibly having to reference QRH in the event that yd-2 also went offline. We took off with the captain flying and me performing pilot not flying duties. Ride conditions were smooth and everything appeared normal until approximately 16;000 ft in the climb; at which time a sudden; abrupt lateral movement was felt. It seemed to be the same symptom as we had experienced on our earlier flight.we verified that yd-1 was still disengaged and yd-2 remained engaged; nevertheless after a few moments we felt another sharp lateral movement. Thinking that we might now have a problem with yd-2; and with no specific QRH procedure available; we reasoned that disconnecting yd-2 might resolve the issue. We disconnected yd-2; which also resulted in disconnection of the autopilot. At first it seemed like the issue was resolved; but after approximately 30-45 seconds the aircraft again abruptly deviated laterally. For a time; the aircraft remained in a skid with the 'brick' displaced to the left; showing that left rudder trim was needed. The captain applied left rudder trim; but the 'brick' unexpectedly moved even further left. The trim was then neutralized; but while EICAS indicated that the rudder trim had returned to neutral; the aircraft continued to skid with the 'brick' displaced to the left. Additional abrupt deviations were felt in both directions for the remainder of the flight with increasing frequency and variable extent.I estimate that on average we experienced these excursions at intervals ranging from approximately once every 45 seconds to one minute; but with occasional 'bursts' of multiple excursions in the space of 5-10 seconds. The frequency and severity seemed random; both before and after yd-2 was disengaged. I must stress that these events were not related to turbulence; nor were they the result of any control input by the flight crew. I have flown both the crj-200 and 900 series for several years under a wide variety of conditions; however the only time I have encountered similar symptoms was during my initial simulator training while the sim instructor was demonstrating flight with both yaw dampers disengaged and my sim partner kicked the rudder pedals sharply (as directed by the sim instructor).the excursions we experienced were spontaneous and on occasion quite violent; sometimes resulting in approximately 15-degrees of heading change in one second with no apparent change in track. We appeared to have a primary flight control malfunction with an unknown cause producing unpredictable effects; and were concerned that the excursions might worsen and perhaps eventually become unrecoverable. We decided it would be prudent to land the aircraft as soon as practicable. The next airport on our route was directly ahead of us about 15 minutes flying time; we declared an emergency and initially requested clearance there; and began a descent to 10;000 ft. We were cleared as requested; but while descending we realized another airport was considerably closer (approximately 20 NM away); and also had a long runway (12;600 ft). We decided to go there instead; and were re-cleared direct to that airport; then handed off to approach. We requested weather; which was reported as wind calm; BKN027; 10SM; and we were told to expect an ILS approach. We configured the FMS and navigation radios; briefed the flight attendant; and performed the descent and approach checklists. The aircraft continued to exhibit erratic lateral controllability; but the captain was able to hand-fly to the final approach course and join the localizer inbound. We decided to land at flaps 20; because we believed we might retain better controllability with a faster approach speed and the resultant higher airflow and a flatter touchdown profile. We also referenced QRH because with both yaw dampers disengaged we had the yaw damper caution message displayed; and this procedure directs a landing at flaps 20. We completed the approach and landed under control; rolled out and cleared the runway; and were directed by ground crew to a hardstand. Knowing that maintaining [electrical] power was essential to preserving any fault codes; we kept the APU running for an hour or more while waiting for a ground power unit to become available. After establishing ground power we handed the airplane over to the ground personnel; having explained to them that it was imperative that the [electrical] power remain on until maintenance arrived.

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Original NASA ASRS Text

Title: A Captain and First Officer report experiencing sudden; sharp; uncommanded lateral rudder inputs while flying a CRJ-200 aircraft during a revenue and ferry flight. Uncommanded lateral movements kept recurring every 30 to 60 seconds even with yaw dampers-1 and -2 and autopilot disengaged. No QRH procedure available to remedy malfunction. Emergency landing was declared.

Narrative: How should a flight crew respond when their aircraft suddenly exhibits apparent flight control malfunctions which don't have a corresponding QRH procedure? Here is how we handled the situation when it happened to us: The flight crew consisted of [our] Captain; Flight Attendant and I; as First Officer. During that flight I was pilot flying; and while enroute at FL300 with autopilot engaged; the aircraft suddenly and abruptly yawed first in one direction; then the other; followed by EICAS displaying a Yaw Damper-1 (YD-1) INOP status message. We attempted to reset YD-1; but within moments YD-1 disengaged itself again; with another significant lateral movement of the aircraft and corresponding deviation of the EFIS 'brick'. Moments prior to YD-1 disengaging a mechanical 'shudder' was felt in both rudder pedals.There is no specific QRH procedure for operating with one Yaw Damper INOP; so we referenced QRH 'YAW DAMPER Caution Message' in case we lost the other Yaw Damper; kept YD-1 off; continued to destination and landed there. Contract Maintenance came out; and after troubleshooting it was decided that the aircraft should be ferried under Special Flight Permit with YD-1 disengaged. As YD-1 was to remain disengaged; we briefed the departure at the gate to include possibly having to reference QRH in the event that YD-2 also went offline. We took off with the Captain flying and me performing pilot not flying duties. Ride conditions were smooth and everything appeared normal until approximately 16;000 FT in the climb; at which time a sudden; abrupt lateral movement was felt. It seemed to be the same symptom as we had experienced on our earlier flight.We verified that YD-1 was still disengaged and YD-2 remained engaged; nevertheless after a few moments we felt another sharp lateral movement. Thinking that we might now have a problem with YD-2; and with no specific QRH procedure available; we reasoned that disconnecting YD-2 might resolve the issue. We disconnected YD-2; which also resulted in disconnection of the autopilot. At first it seemed like the issue was resolved; but after approximately 30-45 seconds the aircraft again abruptly deviated laterally. For a time; the aircraft remained in a skid with the 'brick' displaced to the left; showing that left rudder trim was needed. The Captain applied left rudder trim; but the 'brick' unexpectedly moved even further left. The trim was then neutralized; but while EICAS indicated that the rudder trim had returned to neutral; the aircraft continued to skid with the 'brick' displaced to the left. Additional abrupt deviations were felt in both directions for the remainder of the flight with increasing frequency and variable extent.I estimate that on average we experienced these excursions at intervals ranging from approximately once every 45 seconds to one minute; but with occasional 'bursts' of multiple excursions in the space of 5-10 seconds. The frequency and severity seemed random; both before and after YD-2 was disengaged. I must stress that these events were not related to turbulence; nor were they the result of any control input by the flight crew. I have flown both the CRJ-200 and 900 series for several years under a wide variety of conditions; however the only time I have encountered similar symptoms was during my initial simulator training while the SIM instructor was demonstrating flight with both Yaw Dampers disengaged and my SIM partner kicked the rudder pedals sharply (as directed by the SIM instructor).The excursions we experienced were spontaneous and on occasion quite violent; sometimes resulting in approximately 15-degrees of heading change in one second with no apparent change in track. We appeared to have a Primary Flight Control malfunction with an unknown cause producing unpredictable effects; and were concerned that the excursions might worsen and perhaps eventually become unrecoverable. We decided it would be prudent to land the aircraft as soon as practicable. The next airport on our route was directly ahead of us about 15 minutes flying time; we declared an Emergency and initially requested clearance there; and began a descent to 10;000 FT. We were cleared as requested; but while descending we realized another airport was considerably closer (approximately 20 NM away); and also had a long runway (12;600 FT). We decided to go there instead; and were re-cleared direct to that airport; then handed off to Approach. We requested weather; which was reported as wind calm; BKN027; 10SM; and we were told to expect an ILS approach. We configured the FMS and NAV radios; briefed the Flight Attendant; and performed the Descent and Approach Checklists. The aircraft continued to exhibit erratic lateral controllability; but the Captain was able to hand-fly to the final approach course and join the localizer inbound. We decided to land at Flaps 20; because we believed we might retain better controllability with a faster approach speed and the resultant higher airflow and a flatter touchdown profile. We also referenced QRH because with both Yaw Dampers disengaged we had the YAW DAMPER Caution message displayed; and this procedure directs a landing at Flaps 20. We completed the approach and landed under control; rolled out and cleared the runway; and were directed by Ground crew to a hardstand. Knowing that maintaining [electrical] power was essential to preserving any fault codes; we kept the APU running for an hour or more while waiting for a Ground Power Unit to become available. After establishing Ground Power we handed the airplane over to the ground personnel; having explained to them that it was imperative that the [electrical] power remain on until Maintenance arrived.

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.