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.