Yaw damper fails at FL370 on a B727.

Attributes
ACN	349921
Time
Date	199610
Day	Tue
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : dvc
State Reference	CO
Altitude	msl bound lower : 29000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	349921
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Climbing through FL330 to FL370, control column gradually displaced 20 degrees to left, autoplt on, 3-4 degrees of left rudder. Trim did not help. Fuel balanced. First officer disconnected autoplt and remarked aircraft not responding to trim attempts. Aircraft began 30 plus degree rolls in each direction without pilot input. I requested a descent to FL330 which we received almost immediately. During descent, first officer had a 'handful of aircraft' and did a great job, sleeping passenger not awakened. Prior to FL330 I noticed lower rudder indice displaced more than one width of indice from upper rudder. Turned off lower yaw damper. All controls normal. Both indices married. Less than 1 degree of rudder trim required. Descended to FL240, 280 KTS. Completed abnormal checklist. Called dispatch/atl maintenance coordinator. Rest of flight uneventful. Comments: 1) we might have caught the rudder displacement earlier, but at XA00 things process slower. 2) crew involved with FAA 'downing' aircraft in las for maintenance problems. We switched equipment and were 1.5 hours delayed. 3) when pilots are involved with control problem of aircraft at FL370, it is difficult to split your thinking into analyzing problem and attempting to control aircraft. 4) I chose not to take control of aircraft from first officer because of his experience level, and because it was not necessary. I would have taken the aircraft from a new first officer. 5) briefed all flight attendants on problem and our decision to continue to mci. 6) no comments at all from passenger upon deplaning. Callback conversation with reporter revealed the following information: reporter states that it took the flight crew a period of time to analyze what the difficulty in flying the aircraft was being caused by. It was when the trim indices for the rudder were displaced that the captain believed the lower yaw damper might be faulty. When descending the lower yaw damper was turned off and the aircraft stopped its dutch roll at FL330. Reporter continued descent to FL290 as that is the maximum altitude for a yaw damper inoperative limitation.

Original NASA ASRS Text

Title: YAW DAMPER FAILS AT FL370 ON A B727.

Narrative: CLBING THROUGH FL330 TO FL370, CTL COLUMN GRADUALLY DISPLACED 20 DEGS TO L, AUTOPLT ON, 3-4 DEGS OF L RUDDER. TRIM DID NOT HELP. FUEL BALANCED. FO DISCONNECTED AUTOPLT AND REMARKED ACFT NOT RESPONDING TO TRIM ATTEMPTS. ACFT BEGAN 30 PLUS DEG ROLLS IN EACH DIRECTION WITHOUT PLT INPUT. I REQUESTED A DSCNT TO FL330 WHICH WE RECEIVED ALMOST IMMEDIATELY. DURING DSCNT, FO HAD A 'HANDFUL OF ACFT' AND DID A GREAT JOB, SLEEPING PAX NOT AWAKENED. PRIOR TO FL330 I NOTICED LOWER RUDDER INDICE DISPLACED MORE THAN ONE WIDTH OF INDICE FROM UPPER RUDDER. TURNED OFF LOWER YAW DAMPER. ALL CTLS NORMAL. BOTH INDICES MARRIED. LESS THAN 1 DEG OF RUDDER TRIM REQUIRED. DSNDED TO FL240, 280 KTS. COMPLETED ABNORMAL CHKLIST. CALLED DISPATCH/ATL MAINT COORDINATOR. REST OF FLT UNEVENTFUL. COMMENTS: 1) WE MIGHT HAVE CAUGHT THE RUDDER DISPLACEMENT EARLIER, BUT AT XA00 THINGS PROCESS SLOWER. 2) CREW INVOLVED WITH FAA 'DOWNING' ACFT IN LAS FOR MAINT PROBS. WE SWITCHED EQUIP AND WERE 1.5 HRS DELAYED. 3) WHEN PLTS ARE INVOLVED WITH CTL PROB OF ACFT AT FL370, IT IS DIFFICULT TO SPLIT YOUR THINKING INTO ANALYZING PROB AND ATTEMPTING TO CTL ACFT. 4) I CHOSE NOT TO TAKE CTL OF ACFT FROM FO BECAUSE OF HIS EXPERIENCE LEVEL, AND BECAUSE IT WAS NOT NECESSARY. I WOULD HAVE TAKEN THE ACFT FROM A NEW FO. 5) BRIEFED ALL FLT ATTENDANTS ON PROB AND OUR DECISION TO CONTINUE TO MCI. 6) NO COMMENTS AT ALL FROM PAX UPON DEPLANING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT IT TOOK THE FLC A PERIOD OF TIME TO ANALYZE WHAT THE DIFFICULTY IN FLYING THE ACFT WAS BEING CAUSED BY. IT WAS WHEN THE TRIM INDICES FOR THE RUDDER WERE DISPLACED THAT THE CAPT BELIEVED THE LOWER YAW DAMPER MIGHT BE FAULTY. WHEN DSNDING THE LOWER YAW DAMPER WAS TURNED OFF AND THE ACFT STOPPED ITS DUTCH ROLL AT FL330. RPTR CONTINUED DSCNT TO FL290 AS THAT IS THE MAX ALT FOR A YAW DAMPER INOP LIMITATION.

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.