Narrative:

We were maintenance ferrying an airplane with a landing gear vibration history from clt to gso. Level at 10000 ft and 300 KIAS, we noticed the airplane was yawing rapidly 5-10 degrees left and right. The yaw rate indice was moving so rapidly it was almost a blur. I turned off the yaw damper and the rapid yawing stopped immediately. The yaw indice was now parked 1/2 scale to the right and the airplane was yawing very slightly to the left. Using rudder trim was not effective in trimming the rudder. It either moved the nose too far right or too far left, the effect being that I could not get the airplane into rudder trim. I turned 1 hydraulic rudder control switch off, then the second one off, placing the rudder into the manual reversion mode. We could not move the rudder off center, even both pilots pushing as hard as we could. We slowed to 250 KIAS and still could not budge the rudder. Slowing to 230 KIAS did not help either. I re-pwred the rudder, it worked, but was still cocked slightly to the left. I wrote the problem up in the maintenance logbook and left a final sentence saying that the airplane should be test flown before flying any revenue flts again to ensure that the manual reversion mode of the rudder was working properly. Maintenance agreed with my assessment. The next day maintenance was able to duplicate the flutter and isolate a faulty yaw damper computer and worn components in the rudder actuation system. The FAA is criticizing me for trouble shooting the system by placing the rudder into the manual reversion mode. I feel I had moral responsibility to do this. At least 2 fatal crashes have occurred from this type of failure in the past. I just did not want to take any chances. Callback conversation with reporter revealed the following information: the reporter had just leveled off and established the aircraft in cruise at 300 KIAS at 10000 ft. He slid his seat back and had given control to the first officer so that he could get out the necessary approach charts for their destination. Just after he started to review the charts the first officer asked him to 'look at this.' the aircraft was yawing 5 or 6 degrees left and right very rapidly. The yaw damper indicator was moving so fast it was a 'blur' to the reporter. They switched off the yaw damper and that solved the yaw problem, but the rudder stayed 5 degrees left of center position. Attempts to center the rudder by use of rudder trim were unsuccessful. The flight crew next attempted to determine if one or both hydraulic system were displacing the rudder by shutting off the system one at a time and finally ending in manual reversion. In this condition the flight crew found that they could not move the rudder so they put the hydraulics back on. They decided to accept the rudder displacement and made a normal landing at gso. Maintenance found that the yaw damper computer's variable rate transducer had failed and that some of the spring pwred rudder centering mechanism was worn beyond limits. The FAA, the company and the manufacturer have investigated this incident. The company management and the FAA feel that the flight crew went a bit far in their investigation of the manual reversion potential of the rudder system, but the captain thinks that given the same situation he would probably do a similar check. The manufacturer, however, has accused the company of poor maintenance practices and improper training (the FAA does not concur). The manufacturer has accused the captain of endangering their reputation and attempting to discredit their aircraft. They have revealed to the flight department's surprise that manual reversion of the rudder is only effective below 200 KIAS. Supplemental information from acn 310634: we were level at 10000 ft and 300 KIAS when the nose began to yaw rapidly left and right. The captain turned off the yaw damper and the yawing stopped but the rudder was cocked off to the left. The captain de-pwred the rudder to manual reversion and it centered up. At 300 KIAS we could not budge the rudder, nor at 250 KIAS, nor at 230 KIAS. We re-pwred the rudder system and made an uneventful landing with the yaw damper off.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACFT EQUIP PROB -- ON A FERRY FLT THIS ACR CREW EXPERIENCES YAW DAMPER AND RUDDER MANUAL REVERSION MALFUNCTIONS, BUT THEY MANAGE TO LAND SAFELY.

Narrative: WE WERE MAINT FERRYING AN AIRPLANE WITH A LNDG GEAR VIBRATION HISTORY FROM CLT TO GSO. LEVEL AT 10000 FT AND 300 KIAS, WE NOTICED THE AIRPLANE WAS YAWING RAPIDLY 5-10 DEGS L AND R. THE YAW RATE INDICE WAS MOVING SO RAPIDLY IT WAS ALMOST A BLUR. I TURNED OFF THE YAW DAMPER AND THE RAPID YAWING STOPPED IMMEDIATELY. THE YAW INDICE WAS NOW PARKED 1/2 SCALE TO THE R AND THE AIRPLANE WAS YAWING VERY SLIGHTLY TO THE L. USING RUDDER TRIM WAS NOT EFFECTIVE IN TRIMMING THE RUDDER. IT EITHER MOVED THE NOSE TOO FAR R OR TOO FAR L, THE EFFECT BEING THAT I COULD NOT GET THE AIRPLANE INTO RUDDER TRIM. I TURNED 1 HYD RUDDER CTL SWITCH OFF, THEN THE SECOND ONE OFF, PLACING THE RUDDER INTO THE MANUAL REVERSION MODE. WE COULD NOT MOVE THE RUDDER OFF CTR, EVEN BOTH PLTS PUSHING AS HARD AS WE COULD. WE SLOWED TO 250 KIAS AND STILL COULD NOT BUDGE THE RUDDER. SLOWING TO 230 KIAS DID NOT HELP EITHER. I RE-PWRED THE RUDDER, IT WORKED, BUT WAS STILL COCKED SLIGHTLY TO THE L. I WROTE THE PROB UP IN THE MAINT LOGBOOK AND LEFT A FINAL SENTENCE SAYING THAT THE AIRPLANE SHOULD BE TEST FLOWN BEFORE FLYING ANY REVENUE FLTS AGAIN TO ENSURE THAT THE MANUAL REVERSION MODE OF THE RUDDER WAS WORKING PROPERLY. MAINT AGREED WITH MY ASSESSMENT. THE NEXT DAY MAINT WAS ABLE TO DUPLICATE THE FLUTTER AND ISOLATE A FAULTY YAW DAMPER COMPUTER AND WORN COMPONENTS IN THE RUDDER ACTUATION SYS. THE FAA IS CRITICIZING ME FOR TROUBLE SHOOTING THE SYS BY PLACING THE RUDDER INTO THE MANUAL REVERSION MODE. I FEEL I HAD MORAL RESPONSIBILITY TO DO THIS. AT LEAST 2 FATAL CRASHES HAVE OCCURRED FROM THIS TYPE OF FAILURE IN THE PAST. I JUST DID NOT WANT TO TAKE ANY CHANCES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR HAD JUST LEVELED OFF AND ESTABLISHED THE ACFT IN CRUISE AT 300 KIAS AT 10000 FT. HE SLID HIS SEAT BACK AND HAD GIVEN CTL TO THE FO SO THAT HE COULD GET OUT THE NECESSARY APCH CHARTS FOR THEIR DEST. JUST AFTER HE STARTED TO REVIEW THE CHARTS THE FO ASKED HIM TO 'LOOK AT THIS.' THE ACFT WAS YAWING 5 OR 6 DEGS L AND R VERY RAPIDLY. THE YAW DAMPER INDICATOR WAS MOVING SO FAST IT WAS A 'BLUR' TO THE RPTR. THEY SWITCHED OFF THE YAW DAMPER AND THAT SOLVED THE YAW PROB, BUT THE RUDDER STAYED 5 DEGS L OF CTR POS. ATTEMPTS TO CTR THE RUDDER BY USE OF RUDDER TRIM WERE UNSUCCESSFUL. THE FLC NEXT ATTEMPTED TO DETERMINE IF ONE OR BOTH HYD SYS WERE DISPLACING THE RUDDER BY SHUTTING OFF THE SYS ONE AT A TIME AND FINALLY ENDING IN MANUAL REVERSION. IN THIS CONDITION THE FLC FOUND THAT THEY COULD NOT MOVE THE RUDDER SO THEY PUT THE HYDS BACK ON. THEY DECIDED TO ACCEPT THE RUDDER DISPLACEMENT AND MADE A NORMAL LNDG AT GSO. MAINT FOUND THAT THE YAW DAMPER COMPUTER'S VARIABLE RATE TRANSDUCER HAD FAILED AND THAT SOME OF THE SPRING PWRED RUDDER CENTERING MECHANISM WAS WORN BEYOND LIMITS. THE FAA, THE COMPANY AND THE MANUFACTURER HAVE INVESTIGATED THIS INCIDENT. THE COMPANY MGMNT AND THE FAA FEEL THAT THE FLC WENT A BIT FAR IN THEIR INVESTIGATION OF THE MANUAL REVERSION POTENTIAL OF THE RUDDER SYS, BUT THE CAPT THINKS THAT GIVEN THE SAME SIT HE WOULD PROBABLY DO A SIMILAR CHK. THE MANUFACTURER, HOWEVER, HAS ACCUSED THE COMPANY OF POOR MAINT PRACTICES AND IMPROPER TRAINING (THE FAA DOES NOT CONCUR). THE MANUFACTURER HAS ACCUSED THE CAPT OF ENDANGERING THEIR REPUTATION AND ATTEMPTING TO DISCREDIT THEIR ACFT. THEY HAVE REVEALED TO THE FLT DEPT'S SURPRISE THAT MANUAL REVERSION OF THE RUDDER IS ONLY EFFECTIVE BELOW 200 KIAS. SUPPLEMENTAL INFO FROM ACN 310634: WE WERE LEVEL AT 10000 FT AND 300 KIAS WHEN THE NOSE BEGAN TO YAW RAPIDLY L AND R. THE CAPT TURNED OFF THE YAW DAMPER AND THE YAWING STOPPED BUT THE RUDDER WAS COCKED OFF TO THE L. THE CAPT DE-PWRED THE RUDDER TO MANUAL REVERSION AND IT CTRED UP. AT 300 KIAS WE COULD NOT BUDGE THE RUDDER, NOR AT 250 KIAS, NOR AT 230 KIAS. WE RE-PWRED THE RUDDER SYS AND MADE AN UNEVENTFUL LNDG WITH THE YAW DAMPER OFF.

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.