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.