A B747-200 received uncommanded yaw damper inputs. The crew followed abnormal procedures and disconnected the lower yaw damper system to regain control.

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Attributes
ACN	633087
Time
Date	200410
Day	Sun
Place
Locale Reference	airport : rjaa.airport
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
Route In Use	enroute : pacific
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : atp pilot : flight engineer pilot : multi engine
Experience	flight time last 90 days : 110 flight time total : 7000
ASRS Report	633087
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi pilot : commercial pilot : flight engineer pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 100 flight time total : 9000 flight time type : 520
ASRS Report	632883
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : trim indicator other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

We were climbing through FL310 when the captain asked the first officer to trim the aircraft. The first officer disconnected the autoplt and it took a lot of rudder trim. There was a movement of the aircraft that surprised the captain and first officer. The captain took control of the aircraft and told the first officer to request clearance to level at FL310. We received clearance and the captain was working to maintain straight and level. The captain said he was getting rudder inputs but not through the pedals. He said to turn off the upper and lower yaw dampers, which I did. I broke out the fom and performed 'uncommanded rudder movement.' it was determined that the lower yaw damper was the problem and with the upper yaw damper on, we continued the flight uneventfully. The appropriate log entries were made. No other abnormalities were observed. Supplemental information from acn 632883: at FL310, B autoplt connected, noticed autoplt needed about 10 degrees wing down to maintain course. Disconnected autoplt and trimmed aircraft. 1 1/2 left rudder trim was needed.

Original NASA ASRS Text

Title: A B747-200 RECEIVED UNCOMMANDED YAW DAMPER INPUTS. THE CREW FOLLOWED ABNORMAL PROCS AND DISCONNECTED THE LOWER YAW DAMPER SYS TO REGAIN CTL.

Narrative: WE WERE CLBING THROUGH FL310 WHEN THE CAPT ASKED THE FO TO TRIM THE ACFT. THE FO DISCONNECTED THE AUTOPLT AND IT TOOK A LOT OF RUDDER TRIM. THERE WAS A MOVEMENT OF THE ACFT THAT SURPRISED THE CAPT AND FO. THE CAPT TOOK CTL OF THE ACFT AND TOLD THE FO TO REQUEST CLRNC TO LEVEL AT FL310. WE RECEIVED CLRNC AND THE CAPT WAS WORKING TO MAINTAIN STRAIGHT AND LEVEL. THE CAPT SAID HE WAS GETTING RUDDER INPUTS BUT NOT THROUGH THE PEDALS. HE SAID TO TURN OFF THE UPPER AND LOWER YAW DAMPERS, WHICH I DID. I BROKE OUT THE FOM AND PERFORMED 'UNCOMMANDED RUDDER MOVEMENT.' IT WAS DETERMINED THAT THE LOWER YAW DAMPER WAS THE PROB AND WITH THE UPPER YAW DAMPER ON, WE CONTINUED THE FLT UNEVENTFULLY. THE APPROPRIATE LOG ENTRIES WERE MADE. NO OTHER ABNORMALITIES WERE OBSERVED. SUPPLEMENTAL INFO FROM ACN 632883: AT FL310, B AUTOPLT CONNECTED, NOTICED AUTOPLT NEEDED ABOUT 10 DEGS WING DOWN TO MAINTAIN COURSE. DISCONNECTED AUTOPLT AND TRIMMED ACFT. 1 1/2 L RUDDER TRIM WAS NEEDED.

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.