B737 crew flew with an MEL'ed inoperative yaw damper.

Attributes
ACN	451190
Time
Date	199910
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sea.airport
State Reference	WA
Altitude	msl single value : 2700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : s46.tracon
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 34r other
Flight Phase	descent : approach
Route In Use	approach : visual approach : instrument precision
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : s46.tracon
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 34r
Flight Phase	descent : approach
Route In Use	approach : instrument precision approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : multi engine pilot : atp
Experience	flight time last 90 days : 250 flight time total : 13950 flight time type : 5750
ASRS Report	451190
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	aircraft equipment problem : critical inflight encounter : turbulence inflight encounter : wake turbulence other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : anomaly accepted
Factors
Maintenance	contributing factor : schedule pressure performance deficiency : scheduled maintenance
Supplementary
Problem Areas	Weather Company Aircraft FAA
Primary Problem	Aircraft

Narrative:

Aircraft dispatched with MEL'ed yaw damper inoperative (no restrs) lax-sea. Filed for FL350, we stayed at FL310 (captain's decision). We were the only aircraft that reported light turbulence. We had an uncomfortable ride -- dutch roll with aircraft nose moving r-l. Ended up at FL280 for better control. Into sea inside neeal to runway 34R flaps 10 degrees, 170 KTS and 2700 ft MSL, at 4 mi in trail of company B737, encountered wake turbulence. Right wing started to drop. Put in counter aileron, added power, stopped descent. Went at 1 DOT high on GS (aircraft still rolling to right, now at 10-15 degrees right wing down). Added more power, more left aileron, plus a very small (just a touch) of left rudder -- speed now 190 KTS, right wing at 25-30 degrees down before aircraft responded! Asked for runway 34L (due to closure, 190 KTS). I would have hoped for an immediate response from aircraft! Talked to maintenance on the ground. All procedures were accomplished by maintenance for yaw damper inoperative. Passed on information to outbound crew. Guess I just hit wingtip vortices/wake turbulence perfectly. Hit his left wing turbulence, followed by his right wing turbulence. WX was clear, surface wind at 350 degrees 9 KTS at XA15.

Original NASA ASRS Text

Title: B737 CREW FLEW WITH AN MEL'ED INOP YAW DAMPER.

Narrative: ACFT DISPATCHED WITH MEL'ED YAW DAMPER INOP (NO RESTRS) LAX-SEA. FILED FOR FL350, WE STAYED AT FL310 (CAPT'S DECISION). WE WERE THE ONLY ACFT THAT RPTED LIGHT TURB. WE HAD AN UNCOMFORTABLE RIDE -- DUTCH ROLL WITH ACFT NOSE MOVING R-L. ENDED UP AT FL280 FOR BETTER CTL. INTO SEA INSIDE NEEAL TO RWY 34R FLAPS 10 DEGS, 170 KTS AND 2700 FT MSL, AT 4 MI IN TRAIL OF COMPANY B737, ENCOUNTERED WAKE TURB. R WING STARTED TO DROP. PUT IN COUNTER AILERON, ADDED PWR, STOPPED DSCNT. WENT AT 1 DOT HIGH ON GS (ACFT STILL ROLLING TO R, NOW AT 10-15 DEGS R WING DOWN). ADDED MORE PWR, MORE L AILERON, PLUS A VERY SMALL (JUST A TOUCH) OF L RUDDER -- SPD NOW 190 KTS, R WING AT 25-30 DEGS DOWN BEFORE ACFT RESPONDED! ASKED FOR RWY 34L (DUE TO CLOSURE, 190 KTS). I WOULD HAVE HOPED FOR AN IMMEDIATE RESPONSE FROM ACFT! TALKED TO MAINT ON THE GND. ALL PROCS WERE ACCOMPLISHED BY MAINT FOR YAW DAMPER INOP. PASSED ON INFO TO OUTBOUND CREW. GUESS I JUST HIT WINGTIP VORTICES/WAKE TURB PERFECTLY. HIT HIS L WING TURB, FOLLOWED BY HIS R WING TURB. WX WAS CLR, SURFACE WIND AT 350 DEGS 9 KTS AT XA15.

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.