A DC9-30 climbing through 1000 ft AGL declared an emergency and diverted due to uncommanded rudder inputs causing full yoke displacements to maintain control.

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Attributes
ACN	564136
Time
Date	200210
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 1000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : zzz.tracon tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude climbout : initial
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : private pilot : flight engineer pilot : multi engine pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 240 flight time total : 12000 flight time type : 8000
ASRS Report	564136
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : declared emergency flight crew : diverted to another airport
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Climbing thru 1000 ft AGL the aircraft suffered 3 uncommanded abrupt rudder inputs causing full yoke displacements to maintain control. We climbed to 5000 AGL with flaps extend at 15 and 180 KTS. Dispatch and maintenance control contacted. A failed yaw damper was suspected. Yaw damper turned off along with rudder servo. Aircraft then configured for landing and controlability. Uneventful landing to runway 36L in ZZZ emergency was declared. Callback conversation with reporter revealed the following information: the reporter stated once we recognized the rudder problem the rudder power and the yaw damper were shutoff. The reporter said maintenance found the rudder power unit defective and replaced the unit. The reporter stated this was the first rudder power unit that he was aware of being replaced for failure.

Original NASA ASRS Text

Title: A DC9-30 CLBING THROUGH 1000 FT AGL DECLARED AN EMER AND DIVERTED DUE TO UNCOMMANDED RUDDER INPUTS CAUSING FULL YOKE DISPLACEMENTS TO MAINTAIN CTL.

Narrative: CLBING THRU 1000 FT AGL THE ACFT SUFFERED 3 UNCOMMANDED ABRUPT RUDDER INPUTS CAUSING FULL YOKE DISPLACEMENTS TO MAINTAIN CTL. WE CLBED TO 5000 AGL WITH FLAPS EXTEND AT 15 AND 180 KTS. DISPATCH AND MAINT CTL CONTACTED. A FAILED YAW DAMPER WAS SUSPECTED. YAW DAMPER TURNED OFF ALONG WITH RUDDER SERVO. ACFT THEN CONFIGURED FOR LNDG AND CONTROLABILITY. UNEVENTFUL LNDG TO RWY 36L IN ZZZ EMER WAS DECLARED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED ONCE WE RECOGNIZED THE RUDDER PROB THE RUDDER POWER AND THE YAW DAMPER WERE SHUTOFF. THE RPTR SAID MAINT FOUND THE RUDDER POWER UNIT DEFECTIVE AND REPLACED THE UNIT. THE RPTR STATED THIS WAS THE FIRST RUDDER POWER UNIT THAT HE WAS AWARE OF BEING REPLACED FOR FAILURE.

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.