Narrative:

On feb/xa/00 I worked second shift and was assigned replacement of 'a' system hydraulic return filter. Because I had never performed this job before and no one was assigned to work with me, I first looked up the removal and installation procedures in the maintenance manual. Then I removed the old filter and O rings. Then I replaced them with a new filter and O rings. On several occasions prior to this date, my foreman had given me verbal warnings about taking too much time performing my work. The next work day my foreman explained that the job card replacing 'a' system hydraulic return filter should only take 1 hour to perform. On or about feb/xa/00 the aircraft in question made a test flight. During flight, 'a' system hydraulic pressure was lost and standby system hydraulics were used. An in-flight emergency was declared and the aircraft landed safely. Maintenance employees found that replacing 'a' system hydraulic return filter repaired the loss of pressure. Management tells me that no leaks were found in the preflight checks of 'a' system hydraulics. As of apr/xb/00 I do not know what really caused the aircraft in-flight shutdown. In my experience I have seen sits where the manuals and work cards leave out something which is needed to do the job perfectly.

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Original NASA ASRS Text

Title: A B737-200 ON TEST FLT DECLARED AN EMER AND RETURNED TO THE FIELD DUE TO LOSS OF 'A' SYS PRESSURE AND QUANTITY CAUSED BY INCORRECT FILTER INSTALLATION.

Narrative: ON FEB/XA/00 I WORKED SECOND SHIFT AND WAS ASSIGNED REPLACEMENT OF 'A' SYS HYD RETURN FILTER. BECAUSE I HAD NEVER PERFORMED THIS JOB BEFORE AND NO ONE WAS ASSIGNED TO WORK WITH ME, I FIRST LOOKED UP THE REMOVAL AND INSTALLATION PROCS IN THE MAINT MANUAL. THEN I REMOVED THE OLD FILTER AND O RINGS. THEN I REPLACED THEM WITH A NEW FILTER AND O RINGS. ON SEVERAL OCCASIONS PRIOR TO THIS DATE, MY FOREMAN HAD GIVEN ME VERBAL WARNINGS ABOUT TAKING TOO MUCH TIME PERFORMING MY WORK. THE NEXT WORK DAY MY FOREMAN EXPLAINED THAT THE JOB CARD REPLACING 'A' SYS HYD RETURN FILTER SHOULD ONLY TAKE 1 HR TO PERFORM. ON OR ABOUT FEB/XA/00 THE ACFT IN QUESTION MADE A TEST FLT. DURING FLT, 'A' SYS HYD PRESSURE WAS LOST AND STANDBY SYS HYDS WERE USED. AN INFLT EMER WAS DECLARED AND THE ACFT LANDED SAFELY. MAINT EMPLOYEES FOUND THAT REPLACING 'A' SYS HYD RETURN FILTER REPAIRED THE LOSS OF PRESSURE. MGMNT TELLS ME THAT NO LEAKS WERE FOUND IN THE PREFLT CHKS OF 'A' SYS HYDS. AS OF APR/XB/00 I DO NOT KNOW WHAT REALLY CAUSED THE ACFT INFLT SHUTDOWN. IN MY EXPERIENCE I HAVE SEEN SITS WHERE THE MANUALS AND WORK CARDS LEAVE OUT SOMETHING WHICH IS NEEDED TO DO THE JOB PERFECTLY.

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.