B757-200 crew had uncommanded rudder oscillations after departure.

Attributes
ACN	568987
Time
Date	200212
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dfw.airport
State Reference	TX
Altitude	msl bound lower : 3000 msl bound upper : 4000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : d10.tracon
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Route In Use	departure : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	568987
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : diverted to another airport flight crew : landed as precaution other
Consequence	other other
Supplementary
Problem Areas	Chart Or Publication Company FAA Aircraft
Primary Problem	Aircraft

Narrative:

Captain was PF. After flap retraction, 3000 to 4000 ft MSL, 250 KIAS, ATC instructed right turn heading 280 degrees. Upon entering turn, aircraft began to oscillate/shimmy 2 times per second, rather violently, similar to wake encounter, decreased slightly, then increased again and continued to fishtail per aft flight attendant for about 30 seconds. Aircraft returned to normal flight. Decided to make precautionary return to dfw. On very short final, aircraft began similar fishtailing, but not as severe as first encounter. This was below 50 ft AGL right before touchdown. Had reviewed overweight landing in QRH before landing. Landed flaps 25 degrees, 217500 pounds weight, very soft touchdown at about 50 FPM descent. Returned to gate and briefed maintenance on oscillation and overweight landing. Callback conversation with reporter revealed the following information: the pilot reports they did not have time to deactivate the yaw damper system. They do not know whether this had anything to do with the problem or not. The reporter inspected the aircraft maintenance logs. All 3 rudder power control units were replaced. The aircraft was then test flown, with no repeat of the problem. The B757 has no abnormal or emergency procedure for uncommanded rudder actuation that some other aircraft have.

Original NASA ASRS Text

Title: B757-200 CREW HAD UNCOMMANDED RUDDER OSCILLATIONS AFTER DEP.

Narrative: CAPT WAS PF. AFTER FLAP RETRACTION, 3000 TO 4000 FT MSL, 250 KIAS, ATC INSTRUCTED R TURN HDG 280 DEGS. UPON ENTERING TURN, ACFT BEGAN TO OSCILLATE/SHIMMY 2 TIMES PER SECOND, RATHER VIOLENTLY, SIMILAR TO WAKE ENCOUNTER, DECREASED SLIGHTLY, THEN INCREASED AGAIN AND CONTINUED TO FISHTAIL PER AFT FLT ATTENDANT FOR ABOUT 30 SECONDS. ACFT RETURNED TO NORMAL FLT. DECIDED TO MAKE PRECAUTIONARY RETURN TO DFW. ON VERY SHORT FINAL, ACFT BEGAN SIMILAR FISHTAILING, BUT NOT AS SEVERE AS FIRST ENCOUNTER. THIS WAS BELOW 50 FT AGL RIGHT BEFORE TOUCHDOWN. HAD REVIEWED OVERWT LNDG IN QRH BEFORE LNDG. LANDED FLAPS 25 DEGS, 217500 LBS WT, VERY SOFT TOUCHDOWN AT ABOUT 50 FPM DSCNT. RETURNED TO GATE AND BRIEFED MAINT ON OSCILLATION AND OVERWT LNDG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE PLT RPTS THEY DID NOT HAVE TIME TO DEACTIVATE THE YAW DAMPER SYS. THEY DO NOT KNOW WHETHER THIS HAD ANYTHING TO DO WITH THE PROB OR NOT. THE RPTR INSPECTED THE ACFT MAINT LOGS. ALL 3 RUDDER PWR CTL UNITS WERE REPLACED. THE ACFT WAS THEN TEST FLOWN, WITH NO REPEAT OF THE PROB. THE B757 HAS NO ABNORMAL OR EMER PROC FOR UNCOMMANDED RUDDER ACTUATION THAT SOME OTHER ACFT HAVE.

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.