Narrative:

The first officer was the pilot flying. We were cleared to climb to FL300 in an ATC directed turn; with the center autopilot engaged. Flight conditions were scattered clouds and light chop. The seat belt sign was on. Climbing through FL260 we felt a sudden; extreme; un-commanded yaw of the aircraft. Approximately 30 seconds later there was a second extreme momentary yaw of the aircraft. There were no status messages or any other indications that we could see. The flight control schematic looked normal. We completed our turn and rolled wings level. Within seconds there was a third violent yaw that I would classify as an upset. The autopilot disengaged; the caution status message 'left yaw damper' appeared on the EICAS panel; and the left yaw damper inoperative light illuminated on the overhead panel. The first officer immediately rolled wings level and I directed him to level off at FL270 and slow to 280 KTS. After establishing that the aircraft was stable; I directed the first officer to engage the center autopilot. I coordinated with ATC to maintain this altitude and speed. I told the first officer to continue flying the aircraft and the relief pilot and I would work the malfunction. The relief pilot and I ran the checklist for the left yaw damper inoperative; which directed us to turn off the left yaw damper on the over head panel. We also reviewed the maintenance manual for further guidance. The aircraft was stable; so I directed the first officer to continue flying the aircraft and the relief pilot to monitor both the radios and back up the pilot flying. I then contacted dispatch and the maintenance coordinator. The maintenance coordinator told me that this ship had a history of doing this and that ours was the third such incident. His recommendation was that we continue the flight with the left yaw damper off.I was not comfortable with this assessment for numerous reasons:1. I have experienced yaw damper malfunctions on several other aircraft including the 767/757 and none of my previous occurrences approached this severity.2. There was the week long history of this flight control malfunction. Maintenance informed me on the radio phone conference that over the course of the week they had changed numerous components of the system without fixing the problem.3. We were flight planned for an oceanic crossing and the unique divert issues mechanical malfunctions can present. From the nature of the incident and the failure of multiple attempts to correct the mechanical problem; I was not convinced that it was a simple yaw damper problem and that we possibly had a more severe primary flight control issue.I spoke to ATC to coordinate the return to field. Through both voice communications and ACARS; dispatch and maintenance approved an overweight landing of approximately 10;000-15;000 pounds over max normal landing weight. The relief pilot and I went over all applicable procedures in all available manuals. I declared an emergency for both a possible flight control problem and the overweight landing. The QRH said we might have over-heated brakes. We descended to a lower altitude to burn off as much fuel as possible. We asked for the longest runway and were vectored for a 16 mile right base. I assumed control of the aircraft on downwind and flew the rest of the approach using normal procedures. I disconnected the autopilot on short final to duck slightly under glide slope to shallow out our landing. Sink and speed were normal for a flaps 25 landing. Touchdown was in normal range and there were no GPWS warnings. I disconnected the auto-brakes at 100 KTS and rolled to the end of the runway using spoilers and thrust reversers. We were at 15 KTS at the end of the rollout. We cleared the runway; told ground to terminate the emergency; and continued to the gate.when we arrived at the gate; I spoke to the purser; flight attendants; and also station personal concerning the situation. Several of the flight attendants told me that they had been knocked off balance during the event. The seat belt sign was on; but they had been standing in the galleys during the rudder movement. I then spoke to local maintenance. They repeated their desire to 'maintenance carry over' the left yaw damper. I told them that I would not accept the plane without identifying and fixing the exact problem. I told them that another round of in-exact guess work was unacceptable to me. The nature of a primary flight control malfunction is far too serious for this.the first officer and I arrived at the aircraft the next day in the late afternoon. I had a difficult time arranging transportation and did not receive a briefing from maintenance. I thoroughly reviewed the aircraft forms and was somewhat surprised. The previous night; maintenance had determined that it was probably the left yaw damper causing the problem. They replaced the yaw damper module with a replacement from company stores; but that did not solve the problem. They did other work on the rudder including; I believe; the servo or actuator. They worked on the ship 9-10 hours that day. The ship was not signed off on the maintenance computer until we arrived. We flew the plane uneventfully; with no problems noted. I strongly feel that I was not supported by my airline's maintenance control for my return to base after takeoff. This was a serious aircraft control problem. This flight control malfunction should have been thoroughly investigated and repaired a week earlier; which would have avoided the flight cancellation that caused problems for the passengers; and cost to the company. I strongly feel that if I had continued with this malfunction unresolved; it could have led to serious consequences for the aircraft and all on board.

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Original NASA ASRS Text

Title: B767 Captain experiences three hard over rudder events during climb through FL260. The third event is violent and causes the autopilot to disengage and the yaw damper INOP light to illuminate. After discussions with Maintenance; it is learned that the aircraft has had previous similar incidents and the Captain elects to return to departure airport for an overweight landing.

Narrative: The First Officer was the pilot flying. We were cleared to climb to FL300 in an ATC directed turn; with the center autopilot engaged. Flight conditions were scattered clouds and light chop. The seat belt sign was on. Climbing through FL260 we felt a sudden; extreme; un-commanded yaw of the aircraft. Approximately 30 seconds later there was a second extreme momentary yaw of the aircraft. There were no status messages or any other indications that we could see. The flight control schematic looked normal. We completed our turn and rolled wings level. Within seconds there was a third violent yaw that I would classify as an upset. The autopilot disengaged; the caution status message 'left yaw damper' appeared on the EICAS panel; and the left yaw damper INOP light illuminated on the overhead panel. The First Officer immediately rolled wings level and I directed him to level off at FL270 and slow to 280 KTS. After establishing that the aircraft was stable; I directed the First Officer to engage the center autopilot. I coordinated with ATC to maintain this altitude and speed. I told the First Officer to continue flying the aircraft and the Relief Pilot and I would work the malfunction. The Relief Pilot and I ran the checklist for the left yaw damper INOP; which directed us to turn off the left yaw damper on the over head panel. We also reviewed the Maintenance Manual for further guidance. The aircraft was stable; so I directed the First Officer to continue flying the aircraft and the Relief Pilot to monitor both the radios and back up the pilot flying. I then contacted Dispatch and the Maintenance Coordinator. The Maintenance Coordinator told me that this ship had a history of doing this and that ours was the third such incident. His recommendation was that we continue the flight with the left yaw damper off.I was not comfortable with this assessment for numerous reasons:1. I have experienced yaw damper malfunctions on several other aircraft including the 767/757 and none of my previous occurrences approached this severity.2. There was the week long history of this flight control malfunction. Maintenance informed me on the radio phone conference that over the course of the week they had changed numerous components of the system without fixing the problem.3. We were flight planned for an oceanic crossing and the unique divert issues mechanical malfunctions can present. From the nature of the incident and the failure of multiple attempts to correct the mechanical problem; I was not convinced that it was a simple yaw damper problem and that we possibly had a more severe primary flight control issue.I spoke to ATC to coordinate the return to field. Through both voice communications and ACARS; Dispatch and Maintenance approved an overweight landing of approximately 10;000-15;000 LBS over max normal landing weight. The Relief Pilot and I went over all applicable procedures in all available manuals. I declared an emergency for both a possible flight control problem and the overweight landing. The QRH said we might have over-heated brakes. We descended to a lower altitude to burn off as much fuel as possible. We asked for the longest runway and were vectored for a 16 mile right base. I assumed control of the aircraft on downwind and flew the rest of the approach using normal procedures. I disconnected the autopilot on short final to duck slightly under glide slope to shallow out our landing. Sink and speed were normal for a flaps 25 landing. Touchdown was in normal range and there were no GPWS warnings. I disconnected the auto-brakes at 100 KTS and rolled to the end of the runway using spoilers and thrust reversers. We were at 15 KTS at the end of the rollout. We cleared the runway; told Ground to terminate the emergency; and continued to the gate.When we arrived at the gate; I spoke to the Purser; flight attendants; and also station personal concerning the situation. Several of the flight attendants told me that they had been knocked off balance during the event. The seat belt sign was on; but they had been standing in the galleys during the rudder movement. I then spoke to local Maintenance. They repeated their desire to 'Maintenance carry over' the left yaw damper. I told them that I would not accept the plane without identifying and fixing the exact problem. I told them that another round of in-exact guess work was unacceptable to me. The nature of a primary flight control malfunction is far too serious for this.The First Officer and I arrived at the aircraft the next day in the late afternoon. I had a difficult time arranging transportation and did not receive a briefing from Maintenance. I thoroughly reviewed the aircraft forms and was somewhat surprised. The previous night; Maintenance had determined that it was probably the left yaw damper causing the problem. They replaced the yaw damper module with a replacement from company stores; but that did not solve the problem. They did other work on the rudder including; I believe; the servo or actuator. They worked on the ship 9-10 hours that day. The ship was not signed off on the maintenance computer until we arrived. We flew the plane uneventfully; with no problems noted. I strongly feel that I was not supported by my airline's Maintenance Control for my return to base after takeoff. This was a serious aircraft control problem. This flight control malfunction should have been thoroughly investigated and repaired a week earlier; which would have avoided the flight cancellation that caused problems for the passengers; and cost to the company. I strongly feel that if I had continued with this malfunction unresolved; it could have led to serious consequences for the aircraft and all on board.

Data retrieved from NASA's ASRS site as of April 2012 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.