B737 loses hydraulic pressure in one system.

Attributes
ACN	447641
Time
Date	199908
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : sdf.airport
State Reference	KY
Altitude	msl single value : 26000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : sdf.tracon
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	descent : approach landing : roll
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 240 flight time total : 13000 flight time type : 6000
ASRS Report	447641
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
Independent Detector	aircraft equipment other aircraft equipment : pressure indication other flight crewa
Resolutory Action	controller : issued new clearance flight crew : landed as precaution
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

On descent, 'a' system hydraulic pressure dropped to 1300 psi which resulted in degraded performance of leading edge devices, landing gear and nosewheel steering. Problem was treated as a loss of 'a' system and followed up with loss of 'a' system checklist. A flaps 15 degree landing was made uneventful and aircraft was towed from runway to gate due to lack of nosewheel steering. The following day I discussed the repairs with our maintenance personnel and was informed the problem arose from a faulty 'a' system modulator unit.

Original NASA ASRS Text

Title: B737 LOSES HYD PRESSURE IN ONE SYS.

Narrative: ON DSCNT, 'A' SYS HYD PRESSURE DROPPED TO 1300 PSI WHICH RESULTED IN DEGRADED PERFORMANCE OF LEADING EDGE DEVICES, LNDG GEAR AND NOSEWHEEL STEERING. PROB WAS TREATED AS A LOSS OF 'A' SYS AND FOLLOWED UP WITH LOSS OF 'A' SYS CHKLIST. A FLAPS 15 DEG LNDG WAS MADE UNEVENTFUL AND ACFT WAS TOWED FROM RWY TO GATE DUE TO LACK OF NOSEWHEEL STEERING. THE FOLLOWING DAY I DISCUSSED THE REPAIRS WITH OUR MAINT PERSONNEL AND WAS INFORMED THE PROB AROSE FROM A FAULTY 'A' SYS MODULATOR UNIT.

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.