Regional Jet 900 (CRJ900)
Troubleshooting; Training / Qualification; Confusion; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action; General Maintenance Action
Procedure; MEL; Aircraft
After showing up to start our shift I noticed that Yaw Damper (YD) 1 had been deferred. I briefed the MEL book and verified that 'YD1 inop' status message was indeed illuminated indicating that YD 1 was selected off. All of the MEL parameters had been complied with. After take off the status of the yaw dampers had changed to a yellow caution message. Which led me to believe that neither YD was engaged. The auto pilot would not engage. I reset YD2 and all YD messages were gone I selected YD1 engage so as to disconnect YD1. YD 1 did not disconnect. We continued our climb as we tried to figure out the issue. Finally at flight level 340 we felt uncommanded yaw inputs which were verified by the flight controls EICAS page. There were no abnormal EICAS messages.  We described the situation to Center and requested lower to trouble shoot the problem. After being cleared to FL240 we descended and slowed the aircraft as I searched through the QRH for possible corrective actions. After finding 'uncommanded yaw inputs' I was directed to turn off both yaw dampers. I selected both yaw engage buttons but neither yaw damper disconnected. I tried this several times. I requested priority handling from Center and was cleared direct to our filed destination. We slowed the aircraft to 250 knots as directed by the QRH. Sometime later the YD 1 white status message appeared on EICAS 2We considered deviating and landing at several other airports. After the YD inop status message appeared the uncommanded yaws stopped. Although I did notice that some yaw was occurring on the Flight control page. We continued on to our filed destination and landed without further event.
A CRJ-900 Yaw Damper 1 (YD1) was MEL'ed. After takeoff; YD-2 was engaged which also apparently engaged YD-1. At cruise uncommanded yaw inputs occurred which were verified on the EICAS. The crew descended; completed the UNCOMMANDED YAW INPUT QRH procedure and disconnected both yaw dampers.