Narrative:

Level at FL330 just after exiting an area of light chop we experienced what seemed to be a quick rudder kick. The movement of the aircraft was mild, and neither one of us made mention of it at that time. Within the next 10-15 mins, we experienced the same kick 2 additional times. No pedal movement was ever felt, however, we did notice 1/2 - 3/4 needle deflection of the yaw damper indicator. The movements occurred while we were in and out of light chop. We believed there was a possibility that the kicks were turbulence induced and we discussed this. My captain then told me that if it happened again we would divert to the nearest suitable airport. At this point my captain referenced the flight handbook. The captain then phone patched dispatch and ZZZ and advised them of the situation. ZZZ was unsure of the cause and we discussed the possibility of it being a yaw damper problem, since there was no pedal movement just yaw damper indicator movement. The captain then inquired about aircraft limitations with the yaw damper off. They were unaware of any airspeed or altitude limitations. We told them if it happened again we would turn off the yaw damper, slow, and descend and divert to the nearest suitable airport. No objections were received, end of patch. Approximately 25 mins from top of descent it occurred again. Notified dispatch, slowed, descended, and turned off yaw damper. This time we noticed 1 full needle width deflection. Decided to divert/continue to destination. Asked flight attendants if they felt anything, they said no. Landed uneventfully. Callback conversation with reporter revealed the following information: the reporter states that the air carrier is also extremely interested in irregularities where the rudder may be involved and that upon arriving at the destination a phone conference was initiated with at least 12 persons involved. As a result of this telecon, the yaw damper was determined to be the likely culprit. The yaw damper was thence removed from the aircraft for testing. At this writing, the results are not available. Hopefully, a crew member will notify ASRS when the results become available. At the time of the event, the reporter states that once the yaw damper was disabled, there were no further 'kicks' or indications of rudder displacement. The flight crew was in communication with maintenance while airborne and disconnected the yaw damper in agreement and suggestion of maintenance personnel.

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Original NASA ASRS Text

Title: B737-300 EXPERIENCES MULTIPLE AND PROGRESSIVE RUDDER DISPLACEMENTS WITH MOMENTARY 'QUICK RUDDER KICK' BEFORE LNDG ATL.

Narrative: LEVEL AT FL330 JUST AFTER EXITING AN AREA OF LIGHT CHOP WE EXPERIENCED WHAT SEEMED TO BE A QUICK RUDDER KICK. THE MOVEMENT OF THE ACFT WAS MILD, AND NEITHER ONE OF US MADE MENTION OF IT AT THAT TIME. WITHIN THE NEXT 10-15 MINS, WE EXPERIENCED THE SAME KICK 2 ADDITIONAL TIMES. NO PEDAL MOVEMENT WAS EVER FELT, HOWEVER, WE DID NOTICE 1/2 - 3/4 NEEDLE DEFLECTION OF THE YAW DAMPER INDICATOR. THE MOVEMENTS OCCURRED WHILE WE WERE IN AND OUT OF LIGHT CHOP. WE BELIEVED THERE WAS A POSSIBILITY THAT THE KICKS WERE TURB INDUCED AND WE DISCUSSED THIS. MY CAPT THEN TOLD ME THAT IF IT HAPPENED AGAIN WE WOULD DIVERT TO THE NEAREST SUITABLE ARPT. AT THIS POINT MY CAPT REFED THE FLT HANDBOOK. THE CAPT THEN PHONE PATCHED DISPATCH AND ZZZ AND ADVISED THEM OF THE SIT. ZZZ WAS UNSURE OF THE CAUSE AND WE DISCUSSED THE POSSIBILITY OF IT BEING A YAW DAMPER PROB, SINCE THERE WAS NO PEDAL MOVEMENT JUST YAW DAMPER INDICATOR MOVEMENT. THE CAPT THEN INQUIRED ABOUT ACFT LIMITATIONS WITH THE YAW DAMPER OFF. THEY WERE UNAWARE OF ANY AIRSPD OR ALT LIMITATIONS. WE TOLD THEM IF IT HAPPENED AGAIN WE WOULD TURN OFF THE YAW DAMPER, SLOW, AND DSND AND DIVERT TO THE NEAREST SUITABLE ARPT. NO OBJECTIONS WERE RECEIVED, END OF PATCH. APPROX 25 MINS FROM TOP OF DSCNT IT OCCURRED AGAIN. NOTIFIED DISPATCH, SLOWED, DSNDED, AND TURNED OFF YAW DAMPER. THIS TIME WE NOTICED 1 FULL NEEDLE WIDTH DEFLECTION. DECIDED TO DIVERT/CONTINUE TO DEST. ASKED FLT ATTENDANTS IF THEY FELT ANYTHING, THEY SAID NO. LANDED UNEVENTFULLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATES THAT THE ACR IS ALSO EXTREMELY INTERESTED IN IRREGULARITIES WHERE THE RUDDER MAY BE INVOLVED AND THAT UPON ARRIVING AT THE DEST A PHONE CONFERENCE WAS INITIATED WITH AT LEAST 12 PERSONS INVOLVED. AS A RESULT OF THIS TELECON, THE YAW DAMPER WAS DETERMINED TO BE THE LIKELY CULPRIT. THE YAW DAMPER WAS THENCE REMOVED FROM THE ACFT FOR TESTING. AT THIS WRITING, THE RESULTS ARE NOT AVAILABLE. HOPEFULLY, A CREW MEMBER WILL NOTIFY ASRS WHEN THE RESULTS BECOME AVAILABLE. AT THE TIME OF THE EVENT, THE RPTR STATES THAT ONCE THE YAW DAMPER WAS DISABLED, THERE WERE NO FURTHER 'KICKS' OR INDICATIONS OF RUDDER DISPLACEMENT. THE FLC WAS IN COM WITH MAINT WHILE AIRBORNE AND DISCONNECTED THE YAW DAMPER IN AGREEMENT AND SUGGESTION OF MAINT PERSONNEL.

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.