Narrative:

Arriving at the aircraft we learned the yaw damper was inoperative and the aircraft was being operated under MEL 22-X-xx relief. I reviewed the requirements of the provisos of the MEL and discussed it with the first officer. During the crew briefing with the flight attendants; I informed them of the MEL and inoperative yaw damper and advised they may feel a difference in the rear of the aircraft as a result. I continued that this was the first time I operated the B-737 with an inoperative yaw damper and was unsure of how significant a difference they would notice.we discussed the weather and the existence of a turbulence plot; but dispatch had filed us with ample fuel and at an altitude below the tropopause. They were informed that if the ride did get bumpy; sit immediately and do not wait for us to tell them; but we would communicate with them about any adverse conditions we were informed about as far in advance as possible.during climb to FL300; the flight was normal and without incident. We encountered an occasion light bump and noticed the lack of yaw damper operation was immediately apparent. After reaching FL300; approximately two to three minutes later; the aircraft encountered moderate turbulence. The response from the aircraft was shocking. The tail began to yaw dramatically left; then right; then left. The resulting yaw induced a significant and severe 'dutch roll'. The first officer (PF) instinctively disconnected the autopilot; and attempted to control the aircraft. Seeing the severe yawing and accompanying dutch roll; I instructed him to immediately re-engage the autopilot to prevent pilot induced oscillations and possible loss of control.I made an immediate PA for the flight attendants (flight attendant) to take their seats; contacted center; advised that we were in moderate turbulence and operating with no yaw damper and the aircraft's reaction to the turbulence was unacceptable. ATC issued a descent to FL280. We leveled at FL280 and had another severe dutch roll encounter. We sought and received another descent to FL260. Leveling at FL260; I instructed the first officer to maintain a speed of 280 KIAS or less and be prepared for more turbulence. I then called the flight attendants on the service interphone. Both flight attendant's (front and back) were on the interphone and were extremely shaken by the event. The B or C flight attendant on the line sounded almost panicked. She stated service items were tossed about; but they were able to get into a seat and were uninjured but passengers were getting sick; and were terrified.I made a PA to the passengers explaining that we had encountered clear air turbulence; to keep their seats with their seat belts securely fastened and that the flight attendants would be remaining in their seats as well.the aircraft handled much better at the lower altitude; but a subsequent descent to FL240 was required later to keep the aircraft manageable. I used acars to request voice contact with our dispatcher. Voice contact was established and I informed our dispatcher that it was our intention to continue but if we encountered any more severe yawing/dutch roll we would be diverting immediately. The dispatcher initially was confused and asked if we encountered severe turbulence. I explained that it was moderate turbulence; but a severe reaction by the aircraft to that turbulence. It was agreed that the dispatcher would keep a listening watch on down line frequencies to monitor our progress. Eventually; the ride was smooth and the flight attendants were able to get a service out to the customers.arriving at the gate; I was informed by the flight attendants that the flight was the worst they had ever experienced. They were still shaken by the event. As passengers deplaned; numerous passengers commented on their fear of the situation; but thanked us for getting them safely on the ground. Some of the passengers had gotten airsick as well.in the future I will not accept an aircraft with an inoperative yaw damper if the possibility of adverse weather exists on the route of flight. I fully believed; as did the first officer; that we were on the edge of departing controlled flight at least twice during the event. The apprehension of using manual rudder imputes without a yaw damper; possibly over controlling or experiencing pio; leading to possible aircraft damage or upset is just far too real. I believe it is a real threat to safety operating an aircraft under this MEL when any adverse weather exists.

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Original NASA ASRS Text

Title: B737-300 Captain reports being dispatched with an inoperative yaw damper and encounters moderate turbulence at FL300. The response from the aircraft was shocking with the tail yawing dramatically left; then right; then left producing a significant and severe 'Dutch roll'. Flight descends to a lower altitude and is able to continue to destination. The Dispatchers report is also included.

Narrative: Arriving at the aircraft we learned the yaw damper was inoperative and the aircraft was being operated under MEL 22-X-XX relief. I reviewed the requirements of the provisos of the MEL and discussed it with the First Officer. During the crew briefing with the Flight Attendants; I informed them of the MEL and inoperative yaw damper and advised they may feel a difference in the rear of the aircraft as a result. I continued that this was the first time I operated the B-737 with an inoperative yaw damper and was unsure of how significant a difference they would notice.We discussed the weather and the existence of a turbulence plot; but Dispatch had filed us with ample fuel and at an altitude below the tropopause. They were informed that if the ride did get bumpy; sit immediately and do not wait for us to tell them; but we would communicate with them about any adverse conditions we were informed about as far in advance as possible.During climb to FL300; the flight was normal and without incident. We encountered an occasion light bump and noticed the lack of yaw damper operation was immediately apparent. After reaching FL300; approximately two to three minutes later; the aircraft encountered moderate turbulence. The response from the aircraft was shocking. The tail began to yaw dramatically left; then right; then left. The resulting yaw induced a significant and severe 'Dutch roll'. The First Officer (PF) instinctively disconnected the autopilot; and attempted to control the aircraft. Seeing the severe yawing and accompanying Dutch roll; I instructed him to immediately re-engage the autopilot to prevent Pilot induced oscillations and possible loss of control.I made an immediate PA for the Flight Attendants (FA) to take their seats; contacted Center; advised that we were in moderate turbulence and operating with no yaw damper and the aircraft's reaction to the turbulence was unacceptable. ATC issued a descent to FL280. We leveled at FL280 and had another severe Dutch roll encounter. We sought and received another descent to FL260. Leveling at FL260; I instructed the First Officer to maintain a speed of 280 KIAS or less and be prepared for more turbulence. I then called the Flight Attendants on the service interphone. Both FA's (front and back) were on the interphone and were extremely shaken by the event. The B or C Flight Attendant on the line sounded almost panicked. She stated service items were tossed about; but they were able to get into a seat and were uninjured but Passengers were getting sick; and were terrified.I made a PA to the Passengers explaining that we had encountered clear air turbulence; to keep their seats with their seat belts securely fastened and that the Flight Attendants would be remaining in their seats as well.The aircraft handled much better at the lower altitude; but a subsequent descent to FL240 was required later to keep the aircraft manageable. I used ACARs to request voice contact with our Dispatcher. Voice contact was established and I informed our Dispatcher that it was our intention to continue but if we encountered ANY more severe yawing/Dutch roll we would be diverting immediately. The Dispatcher initially was confused and asked if we encountered severe turbulence. I explained that it was moderate turbulence; but a severe reaction by the aircraft to that turbulence. It was agreed that the Dispatcher would keep a listening watch on down line frequencies to monitor our progress. Eventually; the ride was smooth and the Flight Attendants were able to get a service out to the customers.Arriving at the gate; I was informed by the Flight Attendants that the flight was the worst they had ever experienced. They were still shaken by the event. As Passengers deplaned; numerous Passengers commented on their fear of the situation; but thanked us for getting them safely on the ground. Some of the Passengers had gotten airsick as well.In the future I will not accept an aircraft with an inoperative yaw damper if the possibility of adverse weather exists on the route of flight. I fully believed; as did the First Officer; that we were on the edge of departing controlled flight at least twice during the event. The apprehension of using manual rudder imputes without a yaw damper; possibly over controlling or experiencing PIO; leading to possible aircraft damage or upset is just far too real. I believe it is a real threat to safety operating an aircraft under this MEL when ANY adverse weather exists.

Data retrieved from NASA's ASRS site 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.