A B737-300 descending through 10000 ft declared an emergency due to a 2 second vibration with abrupt...

Attributes
ACN	534091
Time
Date	200112
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 10000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc tracon : zzz.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time type : 1166
ASRS Report	534091
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time type : 827
ASRS Report	534093
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : declared emergency
Consequence	other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Descending through 10000 ft at 250 KIAS, autoplt engaged. A 2 second vibration followed abruptly by a 20 degree right bank when caught by PF using right rudder and disengaging autoplt and autothrottles. Maintained straight and level with left rudder as yoke indicated 6 units right. Declared emergency. After surmising problem trimmed aileron. Uneventful until 30 degree flaps for runway 27R then excessive left rudder required to keep aircraft level as aileron again indicated 6 units right upon landing. Winds 270 degrees 11 KTS clear. Uneventful landing and taxi. Callback conversation with reporter revealed the following information: the reporter stated maintenance removed the airplane from service and accomplished the following: adjusted the autoplt rod servo inputs, aileron position sensors test and adjustment, rig test and adjustment of ailerons, autoplt test, yaw damper test and lvdt test and adjustment, yaw damper servo test. The reporter said the airplane was test flown satisfactory and returned to service.

Original NASA ASRS Text

Title: A B737-300 DSNDING THROUGH 10000 FT DECLARED AN EMER DUE TO A 2 SECOND VIBRATION WITH ABRUPT 20 DEG R BANK CORRECTED WITH R RUDDER. MAINTAINED LEVEL WITH L RUDDER WITH YOKE INDICATING 6 UNITS R. AT 30 DEG FLAPS EXCESSIVE L RUDDER REQUIRED.

Narrative: DSNDING THROUGH 10000 FT AT 250 KIAS, AUTOPLT ENGAGED. A 2 SECOND VIBRATION FOLLOWED ABRUPTLY BY A 20 DEG R BANK WHEN CAUGHT BY PF USING R RUDDER AND DISENGAGING AUTOPLT AND AUTOTHROTTLES. MAINTAINED STRAIGHT AND LEVEL WITH L RUDDER AS YOKE INDICATED 6 UNITS R. DECLARED EMER. AFTER SURMISING PROB TRIMMED AILERON. UNEVENTFUL UNTIL 30 DEG FLAPS FOR RWY 27R THEN EXCESSIVE L RUDDER REQUIRED TO KEEP ACFT LEVEL AS AILERON AGAIN INDICATED 6 UNITS R UPON LNDG. WINDS 270 DEGS 11 KTS CLR. UNEVENTFUL LNDG AND TAXI. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED MAINT REMOVED THE AIRPLANE FROM SVC AND ACCOMPLISHED THE FOLLOWING: ADJUSTED THE AUTOPLT ROD SERVO INPUTS, AILERON POS SENSORS TEST AND ADJUSTMENT, RIG TEST AND ADJUSTMENT OF AILERONS, AUTOPLT TEST, YAW DAMPER TEST AND LVDT TEST AND ADJUSTMENT, YAW DAMPER SERVO TEST. THE RPTR SAID THE AIRPLANE WAS TEST FLOWN SATISFACTORY AND RETURNED TO SVC.

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.

A B737-300 descending through 10000 ft declared an emergency due to a 2 second vibration with abrupt 20 degree right bank corrected with right rudder. Maintained level with left rudder with yoke indicating 6 units right. At 30 degree flaps excessive left rudder required.