An A320 developed a pitch oscillation above M.74. A yellow elevator servo was replaced. Two flts lat...

Attributes
ACN	794866
Time
Date	200806
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zzz.artcc
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	A320
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
ASRS Report	794866
Events
Anomaly	aircraft equipment problem : less severe maintenance problem : improper maintenance
Resolutory Action	aircraft : equipment problem dissipated flight crew : regained aircraft control flight crew : took precautionary avoidance action
Consequence	other
Supplementary
Problem Areas	Maintenance Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

During climb out of ZZZ; the aircraft began oscillating in the pitch axis with autoplt on. This oscillation began as a noticeable slight vibration; increasing exponentially to at least a moderate washboard effect turbulent condition. Switching autoplts had no effect as well as disconnecting autoplt altogether. Slowing to approximately mach .74 seemed to result in smooth flight. Dispatcher was contacted. We pressed on to ZZZ1 with maintenance's blessings. Increasing speed to mach .81 later in the flight had no further effect. Yellow hydraulic pressure noted at 3250 psi. ZZZ replaced hydraulic pump; and found yellow elevator servo to be faulty. All fixed; flight on to lax went without incident. Flight ZZZ2-ZZZ1 had recurring problem we experienced out of ZZZ. Written up in maintenance log briefed oncoming crew. Seat of the pants flying; followed up by interphone calls from cabin; moderate washboard effect type turbulence experienced onboard aircraft.

Original NASA ASRS Text

Title: AN A320 DEVELOPED A PITCH OSCILLATION ABOVE M.74. A YELLOW ELEVATOR SERVO WAS REPLACED. TWO FLTS LATER THE EVENT OCCURRED AGAIN.

Narrative: DURING CLBOUT OF ZZZ; THE ACFT BEGAN OSCILLATING IN THE PITCH AXIS WITH AUTOPLT ON. THIS OSCILLATION BEGAN AS A NOTICEABLE SLIGHT VIBRATION; INCREASING EXPONENTIALLY TO AT LEAST A MODERATE WASHBOARD EFFECT TURBULENT CONDITION. SWITCHING AUTOPLTS HAD NO EFFECT AS WELL AS DISCONNECTING AUTOPLT ALTOGETHER. SLOWING TO APPROX MACH .74 SEEMED TO RESULT IN SMOOTH FLT. DISPATCHER WAS CONTACTED. WE PRESSED ON TO ZZZ1 WITH MAINT'S BLESSINGS. INCREASING SPD TO MACH .81 LATER IN THE FLT HAD NO FURTHER EFFECT. YELLOW HYD PRESSURE NOTED AT 3250 PSI. ZZZ REPLACED HYD PUMP; AND FOUND YELLOW ELEVATOR SERVO TO BE FAULTY. ALL FIXED; FLT ON TO LAX WENT WITHOUT INCIDENT. FLT ZZZ2-ZZZ1 HAD RECURRING PROB WE EXPERIENCED OUT OF ZZZ. WRITTEN UP IN MAINT LOG BRIEFED ONCOMING CREW. SEAT OF THE PANTS FLYING; FOLLOWED UP BY INTERPHONE CALLS FROM CABIN; MODERATE WASHBOARD EFFECT TYPE TURB EXPERIENCED ONBOARD ACFT.

Data retrieved from NASA's ASRS site as of May 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 developed a pitch oscillation above M.74. A yellow elevator servo was replaced. Two flts later the event occurred again.