B747-200 crew had the lower yaw damper malfunction.

Attributes
ACN	633012
Time
Date	200409
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : rjtg.artcc
State Reference	FO
Altitude	msl single value : 31000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : rjtg.artcc
Operator	common carrier : air carrier
Make Model Name	B747-200
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
Experience	controller military : 7 controller radar : 20 flight time last 90 days : 180 flight time total : 12000 flight time type : 4000
ASRS Report	633012
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

During climb out to FL350 with the first officer flying and autoplt B engaged, I noticed the autoplt requiring about a 10 degree right wing down deflection to maintain course. The lower rudder indicator was slightly out to the left. I asked the first officer to check the trim of the aircraft which she did by disconnecting the autoplt and trimming rudder. The aircraft required approximately 1 1/2 units of left rudder trim to maintain wings level. Shortly after the first officer reengaged the B autoplt, we experienced a significant and uncommanded yaw. I took the aircraft, disconnected the autoplt again and stopped the climb. We experienced another yaw. As the so was getting out the communication procedures for the appropriate malfunction checklist, I asked him to disengage the yaw dampers (after the first yaw, I had my feet on the rudders and noted no rudder movement with the second yaw and I know from previous experience that we can operate without either yaw damper). We accomplished the communication procedure 'uncommanded rudder movement' and found that the lower yaw damper was the problem. We operated the remainder of the flight to tpe with the lower yaw damper off. All other system including hydraulics were normal. Also, normal flight control function of both yaw dampers had been observed on the taxi-out check.

Original NASA ASRS Text

Title: B747-200 CREW HAD THE LOWER YAW DAMPER MALFUNCTION.

Narrative: DURING CLBOUT TO FL350 WITH THE FO FLYING AND AUTOPLT B ENGAGED, I NOTICED THE AUTOPLT REQUIRING ABOUT A 10 DEG R WING DOWN DEFLECTION TO MAINTAIN COURSE. THE LOWER RUDDER INDICATOR WAS SLIGHTLY OUT TO THE L. I ASKED THE FO TO CHK THE TRIM OF THE ACFT WHICH SHE DID BY DISCONNECTING THE AUTOPLT AND TRIMMING RUDDER. THE ACFT REQUIRED APPROX 1 1/2 UNITS OF L RUDDER TRIM TO MAINTAIN WINGS LEVEL. SHORTLY AFTER THE FO REENGAGED THE B AUTOPLT, WE EXPERIENCED A SIGNIFICANT AND UNCOMMANDED YAW. I TOOK THE ACFT, DISCONNECTED THE AUTOPLT AGAIN AND STOPPED THE CLB. WE EXPERIENCED ANOTHER YAW. AS THE SO WAS GETTING OUT THE COM PROCS FOR THE APPROPRIATE MALFUNCTION CHKLIST, I ASKED HIM TO DISENGAGE THE YAW DAMPERS (AFTER THE FIRST YAW, I HAD MY FEET ON THE RUDDERS AND NOTED NO RUDDER MOVEMENT WITH THE SECOND YAW AND I KNOW FROM PREVIOUS EXPERIENCE THAT WE CAN OPERATE WITHOUT EITHER YAW DAMPER). WE ACCOMPLISHED THE COM PROC 'UNCOMMANDED RUDDER MOVEMENT' AND FOUND THAT THE LOWER YAW DAMPER WAS THE PROB. WE OPERATED THE REMAINDER OF THE FLT TO TPE WITH THE LOWER YAW DAMPER OFF. ALL OTHER SYS INCLUDING HYDS WERE NORMAL. ALSO, NORMAL FLT CTL FUNCTION OF BOTH YAW DAMPERS HAD BEEN OBSERVED ON THE TAXI-OUT CHK.

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.