Narrative:

While operating a B737-200 on final approach at flaps 5 degrees, 210 KTS, encountered a cyclic yaw oscillation of approximately 5 degrees left and right at a 1 to 2 second interval. Landing was uneventful other than the feeling that the rudder was very ineffective and not responding to inputs. Callback conversation with reporter revealed the following information: the captain said that the first officer was flying the aircraft on approach to gso with the flaps at 5 degrees and the gear up when they first noticed the yaw. The aircraft nose was moving 10-12 degrees left and right. This movement continued through the rest of the flap and gear extension and into the flare and touchdown. The captain said that it was as if the rudder system had a mind of its own. During their brief time of troubleshooting, the flight crew noticed that when they shut off the yaw damper the movement continued and the yaw damper indicator continued to display movement of the rudder. The captain also noticed that when he disconnected the autoplt and re-engaged the yaw damper he could push the rudder pedals 3 to 4 inches in on either side without the rudder itself, apparently, deflecting. The reporter said that he spoke to several maintenance technicians after the flight and one of the engineers said that he had seen this before and it was due to hydraulic fluid contamination. He was later told that the rudder and standby rudder pcus and the yaw damper system had been removed and sent to boeing for further investigation. The reporter wanted to emphasize that he had a great deal of experience with a number of aircraft in the air force and in civilian flying, but this was the first time that he felt that an aircraft was out of control.

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Original NASA ASRS Text

Title: THIS ACR FLC WAS FLYING A B737-200 ON FINAL APCH WHEN IT STARTED YAWING 10 TO 12 DEGS EITHER SIDE. THIS YAWING MOTION CONTINUED THROUGH FLAP AND GEAR EXTENSION AND ALL THE WAY TO TOUCHDOWN. 148 PT 2.

Narrative: WHILE OPERATING A B737-200 ON FINAL APCH AT FLAPS 5 DEGS, 210 KTS, ENCOUNTERED A CYCLIC YAW OSCILLATION OF APPROX 5 DEGS L AND R AT A 1 TO 2 SECOND INTERVAL. LNDG WAS UNEVENTFUL OTHER THAN THE FEELING THAT THE RUDDER WAS VERY INEFFECTIVE AND NOT RESPONDING TO INPUTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT SAID THAT THE FO WAS FLYING THE ACFT ON APCH TO GSO WITH THE FLAPS AT 5 DEGS AND THE GEAR UP WHEN THEY FIRST NOTICED THE YAW. THE ACFT NOSE WAS MOVING 10-12 DEGS L AND R. THIS MOVEMENT CONTINUED THROUGH THE REST OF THE FLAP AND GEAR EXTENSION AND INTO THE FLARE AND TOUCHDOWN. THE CAPT SAID THAT IT WAS AS IF THE RUDDER SYS HAD A MIND OF ITS OWN. DURING THEIR BRIEF TIME OF TROUBLESHOOTING, THE FLC NOTICED THAT WHEN THEY SHUT OFF THE YAW DAMPER THE MOVEMENT CONTINUED AND THE YAW DAMPER INDICATOR CONTINUED TO DISPLAY MOVEMENT OF THE RUDDER. THE CAPT ALSO NOTICED THAT WHEN HE DISCONNECTED THE AUTOPLT AND RE-ENGAGED THE YAW DAMPER HE COULD PUSH THE RUDDER PEDALS 3 TO 4 INCHES IN ON EITHER SIDE WITHOUT THE RUDDER ITSELF, APPARENTLY, DEFLECTING. THE RPTR SAID THAT HE SPOKE TO SEVERAL MAINT TECHNICIANS AFTER THE FLT AND ONE OF THE ENGINEERS SAID THAT HE HAD SEEN THIS BEFORE AND IT WAS DUE TO HYD FLUID CONTAMINATION. HE WAS LATER TOLD THAT THE RUDDER AND STANDBY RUDDER PCUS AND THE YAW DAMPER SYS HAD BEEN REMOVED AND SENT TO BOEING FOR FURTHER INVESTIGATION. THE RPTR WANTED TO EMPHASIZE THAT HE HAD A GREAT DEAL OF EXPERIENCE WITH A NUMBER OF ACFT IN THE AIR FORCE AND IN CIVILIAN FLYING, BUT THIS WAS THE FIRST TIME THAT HE FELT THAT AN ACFT WAS OUT OF CTL.

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.