B737 flight crew had properly deferred yaw damper and maintenance found a hydraulic leak.

Attributes
ACN	475076
Time
Date	200006
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	ground : preflight ground : parked
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : flight engineer pilot : instrument pilot : multi engine pilot : atp
Experience	flight time last 90 days : 150 flight time total : 13800 flight time type : 7000
ASRS Report	475076
Person 2
Affiliation	company : air carrier government : faa government other
Qualification	pilot : instrument pilot : commercial pilot : multi engine
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa other flight crewb other other : 3
Consequence	other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Arrived at aircraft. During preflight, found there to be an MEL with the yaw damper inoperative. I reviewed the logbook and found there to be 2 write-ups concerning the yaw damper. One dated jun/xa/00 and one on jun/xb/00. After the second write-up the yaw damper was placed on MEL and the aircraft was released by maintenance back into service. The first officer and I reviewed our MEL book and found the aircraft could be flown without a yaw damper and there was a special procedure which we reviewed and found it to be a maintenance function. On the ground in ord, a mechanic went into the cockpit and shut down all aircraft power. We asked what was going on and he stated we were leaking fluid from under the APU. I thought he meant we had an APU problem. After 10-15 mins, he returned and told us we had a hydraulic leak and several nuts were hanging by their safety wire in the rudder. We went with him to inspect the tail section. We were lifted via 'cherry picker' to on top of the elevator and were shown where hydraulic fluid had leaked and eaten the paint and a seal away on top of the elevator and through 2 access doors where the nuts were hanging. No way could this have been seen during any normal preflight, with its location being on top of the elevator. At this point, maintenance grounded the aircraft.

Original NASA ASRS Text

Title: B737 FLC HAD PROPERLY DEFERRED YAW DAMPER AND MAINT FOUND A HYD LEAK.

Narrative: ARRIVED AT ACFT. DURING PREFLT, FOUND THERE TO BE AN MEL WITH THE YAW DAMPER INOP. I REVIEWED THE LOGBOOK AND FOUND THERE TO BE 2 WRITE-UPS CONCERNING THE YAW DAMPER. ONE DATED JUN/XA/00 AND ONE ON JUN/XB/00. AFTER THE SECOND WRITE-UP THE YAW DAMPER WAS PLACED ON MEL AND THE ACFT WAS RELEASED BY MAINT BACK INTO SVC. THE FO AND I REVIEWED OUR MEL BOOK AND FOUND THE ACFT COULD BE FLOWN WITHOUT A YAW DAMPER AND THERE WAS A SPECIAL PROC WHICH WE REVIEWED AND FOUND IT TO BE A MAINT FUNCTION. ON THE GND IN ORD, A MECH WENT INTO THE COCKPIT AND SHUT DOWN ALL ACFT PWR. WE ASKED WHAT WAS GOING ON AND HE STATED WE WERE LEAKING FLUID FROM UNDER THE APU. I THOUGHT HE MEANT WE HAD AN APU PROB. AFTER 10-15 MINS, HE RETURNED AND TOLD US WE HAD A HYD LEAK AND SEVERAL NUTS WERE HANGING BY THEIR SAFETY WIRE IN THE RUDDER. WE WENT WITH HIM TO INSPECT THE TAIL SECTION. WE WERE LIFTED VIA 'CHERRY PICKER' TO ON TOP OF THE ELEVATOR AND WERE SHOWN WHERE HYD FLUID HAD LEAKED AND EATEN THE PAINT AND A SEAL AWAY ON TOP OF THE ELEVATOR AND THROUGH 2 ACCESS DOORS WHERE THE NUTS WERE HANGING. NO WAY COULD THIS HAVE BEEN SEEN DURING ANY NORMAL PREFLT, WITH ITS LOCATION BEING ON TOP OF THE ELEVATOR. AT THIS POINT, MAINT GNDED THE ACFT.

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.