An A320 captain describes an airframe vibration and yaw starting at about FL280. Vibration stopped w...

Attributes
ACN	751275
Time
Date	200708
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl bound lower : 28000 msl bound upper : 36000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude cruise : level
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 250 flight time total : 9000 flight time type : 2000
ASRS Report	751275
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control flight crew : took precautionary avoidance action flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Aircraft Maintenance Human Performance
Primary Problem	Aircraft

Narrative:

Between FL280 and FL290; aircraft started vibrating or shaking in yaw. We were flying 300 KIAS ATC assigned speed (about .78M). The vibration checklist was accomplished; and the vibration went away with rudder input in either direction. Higher altitudes and lower speeds both made the vibration less or go away completely. As a test; once at cruise; FL360; we accelerated to .80M. Vibration then was coming in waves; slight then building in intensity to a point; then off. A slow build to a maximum intensity; then stop. Over and over. We slowed to .78 and had no problems whatsoever. Continued to destination where we had agreed with maintenance and chief pilot that it should be parked until fixed. This is the same aircraft that I had the same problem with seven days earlier. It was also written up by another crew the day before.callback conversation with reporter revealed the following information: reporter followed up on the completed maintenance of this aircraft. He discovered that the 'green' and 'blue' rudder actuators were out of tolerance by 12 MM. Also the upper and lower rudder servos and rod ends were replaced. He repeated that the aircraft actions during this event were very pronounced.

Original NASA ASRS Text

Title: AN A320 CAPT DESCRIBES AN AIRFRAME VIBRATION AND YAW STARTING AT ABOUT FL280. VIBRATION STOPPED WHEN MACH/AIRSPEED SET AT .78.

Narrative: BETWEEN FL280 AND FL290; ACFT STARTED VIBRATING OR SHAKING IN YAW. WE WERE FLYING 300 KIAS ATC ASSIGNED SPEED (ABOUT .78M). THE VIBRATION CHECKLIST WAS ACCOMPLISHED; AND THE VIBRATION WENT AWAY WITH RUDDER INPUT IN EITHER DIRECTION. HIGHER ALTITUDES AND LOWER SPEEDS BOTH MADE THE VIBRATION LESS OR GO AWAY COMPLETELY. AS A TEST; ONCE AT CRUISE; FL360; WE ACCELERATED TO .80M. VIBRATION THEN WAS COMING IN WAVES; SLIGHT THEN BUILDING IN INTENSITY TO A POINT; THEN OFF. A SLOW BUILD TO A MAX INTENSITY; THEN STOP. OVER AND OVER. WE SLOWED TO .78 AND HAD NO PROBLEMS WHATSOEVER. CONTINUED TO DEST WHERE WE HAD AGREED WITH MAINT AND CHIEF PLT THAT IT SHOULD BE PARKED UNTIL FIXED. THIS IS THE SAME AIRCRAFT THAT I HAD THE SAME PROBLEM WITH SEVEN DAYS EARLIER. IT WAS ALSO WRITTEN UP BY ANOTHER CREW THE DAY BEFORE.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER FOLLOWED UP ON THE COMPLETED MAINTENANCE OF THIS ACFT. HE DISCOVERED THAT THE 'GREEN' AND 'BLUE' RUDDER ACTUATORS WERE OUT OF TOLERANCE BY 12 MM. ALSO THE UPPER AND LOWER RUDDER SERVOS AND ROD ENDS WERE REPLACED. HE REPEATED THAT THE ACFT ACTIONS DURING THIS EVENT WERE VERY PRONOUNCED.

Data retrieved from NASA's ASRS site as of January 2009 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.

An A320 captain describes an airframe vibration and yaw starting at about FL280. Vibration stopped when mach/airspeed set at .78.