Narrative:

On the morning of jun/xa/00, aircraft xyz (flight XXX) experienced loss of hydraulic pressure after departure from ZZZ airport. The aircraft air-returned to ZZZ and subsequent inspection of the aircraft revealed both hydraulic 'a' and 'B' system pneumatic head pressure relief valves were left in the open (pressure relief) position held with pieces of safety wire. The relief valves were held open in order to change both hydraulic system case drain filters. This was done to accomplish a portion of the A-2 check. After completing the filter change, I failed to return the relief valves to their normal position. Since I did not return relief valves to normal position, aircraft hydraulic system could not maintain constant pressure. Aircraft xyz then returned as soon as problem was recognized. Once aircraft xyz returned, inspection of hydraulic system was accomplished, both 'a' and 'B' system filters were changed and inspected. No damage was evident and aircraft xyz was returned to normal confign to continue flight. Callback conversation with reporter revealed the following information: the reporter stated the job card for the case drain filter replacement gave no directions for depressurization of the reservoirs or where the information could be found.

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Original NASA ASRS Text

Title: A B737-700 WAS DISPATCHED IN NON COMPLIANCE WITH THE 'A' AND 'B' HYD SYS RESERVOIR PRESSURE RELIEF VALVES WIRED OPEN.

Narrative: ON THE MORNING OF JUN/XA/00, ACFT XYZ (FLT XXX) EXPERIENCED LOSS OF HYD PRESSURE AFTER DEP FROM ZZZ ARPT. THE ACFT AIR-RETURNED TO ZZZ AND SUBSEQUENT INSPECTION OF THE ACFT REVEALED BOTH HYD 'A' AND 'B' SYS PNEUMATIC HEAD PRESSURE RELIEF VALVES WERE LEFT IN THE OPEN (PRESSURE RELIEF) POS HELD WITH PIECES OF SAFETY WIRE. THE RELIEF VALVES WERE HELD OPEN IN ORDER TO CHANGE BOTH HYD SYS CASE DRAIN FILTERS. THIS WAS DONE TO ACCOMPLISH A PORTION OF THE A-2 CHK. AFTER COMPLETING THE FILTER CHANGE, I FAILED TO RETURN THE RELIEF VALVES TO THEIR NORMAL POS. SINCE I DID NOT RETURN RELIEF VALVES TO NORMAL POS, ACFT HYD SYS COULD NOT MAINTAIN CONSTANT PRESSURE. ACFT XYZ THEN RETURNED AS SOON AS PROB WAS RECOGNIZED. ONCE ACFT XYZ RETURNED, INSPECTION OF HYD SYS WAS ACCOMPLISHED, BOTH 'A' AND 'B' SYS FILTERS WERE CHANGED AND INSPECTED. NO DAMAGE WAS EVIDENT AND ACFT XYZ WAS RETURNED TO NORMAL CONFIGN TO CONTINUE FLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE JOB CARD FOR THE CASE DRAIN FILTER REPLACEMENT GAVE NO DIRECTIONS FOR DEPRESSURIZATION OF THE RESERVOIRS OR WHERE THE INFO COULD BE FOUND.

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.