Narrative:

Rudder oscillations that required us to turn off yaw damper and powered rudder. Referred to communication (cockpit operating manual) and performed appropriate procedure, discussed situation with dispatcher and company maintenance. Continued flight as scheduled without further problems. Discussed event with head of safety department and base chief pilot. Callback conversation with reporter revealed the following information: the captain was flying a DC9-30 when the rudder moved unexpectedly. The aft cabin attendant reported the movement as the crew started through their uncommanded control movement checklist. Later she came to the flight station and told them of other movement when the crew was following some troubleshooting suggestions from their maintenance control personnel and had turned on the yaw damper and rudder hydraulic power. The unusual movement stopped when the crew turned off the yaw damper and the hydraulic power to the rudder. They informed the dispatcher, maintenance control and ARTCC and continued to destination using manual rudder control. A large group of company and emergency personnel met the aircraft after they arrived and at that time they discovered that the controller had declared an emergency for them. The maintenance personnel could not say what specific failure caused the movement, they were sure that it was a yaw damper component.

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Original NASA ASRS Text

Title: AN ACR DC9 FLC EXPERIENCED UNCOMMANDED RUDDER MOVEMENT THAT, APPARENTLY, ORIGINATED FROM THE YAW DAMPER.

Narrative: RUDDER OSCILLATIONS THAT REQUIRED US TO TURN OFF YAW DAMPER AND POWERED RUDDER. REFERRED TO COM (COCKPIT OPERATING MANUAL) AND PERFORMED APPROPRIATE PROC, DISCUSSED SIT WITH DISPATCHER AND COMPANY MAINT. CONTINUED FLT AS SCHEDULED WITHOUT FURTHER PROBS. DISCUSSED EVENT WITH HEAD OF SAFETY DEPT AND BASE CHIEF PLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT WAS FLYING A DC9-30 WHEN THE RUDDER MOVED UNEXPECTEDLY. THE AFT CABIN ATTENDANT RPTED THE MOVEMENT AS THE CREW STARTED THROUGH THEIR UNCOMMANDED CTL MOVEMENT CHKLIST. LATER SHE CAME TO THE FLT STATION AND TOLD THEM OF OTHER MOVEMENT WHEN THE CREW WAS FOLLOWING SOME TROUBLESHOOTING SUGGESTIONS FROM THEIR MAINT CTL PERSONNEL AND HAD TURNED ON THE YAW DAMPER AND RUDDER HYD PWR. THE UNUSUAL MOVEMENT STOPPED WHEN THE CREW TURNED OFF THE YAW DAMPER AND THE HYD PWR TO THE RUDDER. THEY INFORMED THE DISPATCHER, MAINT CTL AND ARTCC AND CONTINUED TO DEST USING MANUAL RUDDER CTL. A LARGE GROUP OF COMPANY AND EMER PERSONNEL MET THE ACFT AFTER THEY ARRIVED AND AT THAT TIME THEY DISCOVERED THAT THE CTLR HAD DECLARED AN EMER FOR THEM. THE MAINT PERSONNEL COULD NOT SAY WHAT SPECIFIC FAILURE CAUSED THE MOVEMENT, THEY WERE SURE THAT IT WAS A YAW DAMPER COMPONENT.

Data retrieved from NASA's ASRS site as of July 2007 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.