Narrative:

On jan/tue/02, aircraft X #4 engine hydraulic driven pump, came in on a flight with overheat, so I was assigned to work on this aircraft. After running #4 engine we found that the edp (engine driven pump) was not producing hydraulic pressure. So we proceeded to open the cowls and to change the edp. Upon removal of the edp per maintenance manual 29-11-05 and maintenance manual 29-30-00 we did not notice anything out of the ordinary. Hydraulic fluid looked normal. The dpi's (differential pressure indicators, pop out indicator if filter plugged) were normal. All hydraulic lines looked normal no discrepancies found. After installation we motored the engine found no leaks and hydraulic pressure was normal, 3000 psi, then made a write-up for the next shift to run engine for 5 mins and check for leaks. This happened jan/tue/02, and on jan/wed/02, aircraft took off and could not retract r-hand gear door. So returned to field. Then I happened to pick aircraft up at gate and towed to maintenance. Found #4 hydraulic system with adp on was at 2600 psi after 15 mins of running was at 1500 psi on jan/thu/02. Another group of mechanics found contamination and that one of the supply lines was clogged inside. This was on jan/thu/02. Supplemental information from acn 536044: during replacement of #4 edp per maintenance manual 29-11-05, we noticed no discoloration or abnormal smell of skydrol. We noticed no blockage of sludge in the lines. I felt that maintenance manuals were contradicting and not specific concerning specific problems.

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Original NASA ASRS Text

Title: A B747-400 WAS DISPATCHED IN NON COMPLIANCE WITH CONTAMINATED #4 HYD FLUID NOT FOUND DURING #4 ENG DRIVEN PUMP REPLACEMENT.

Narrative: ON JAN/TUE/02, ACFT X #4 ENG HYD DRIVEN PUMP, CAME IN ON A FLT WITH OVERHEAT, SO I WAS ASSIGNED TO WORK ON THIS ACFT. AFTER RUNNING #4 ENG WE FOUND THAT THE EDP (ENG DRIVEN PUMP) WAS NOT PRODUCING HYD PRESSURE. SO WE PROCEEDED TO OPEN THE COWLS AND TO CHANGE THE EDP. UPON REMOVAL OF THE EDP PER MAINT MANUAL 29-11-05 AND MAINT MANUAL 29-30-00 WE DID NOT NOTICE ANYTHING OUT OF THE ORDINARY. HYD FLUID LOOKED NORMAL. THE DPI'S (DIFFERENTIAL PRESSURE INDICATORS, POP OUT INDICATOR IF FILTER PLUGGED) WERE NORMAL. ALL HYD LINES LOOKED NORMAL NO DISCREPANCIES FOUND. AFTER INSTALLATION WE MOTORED THE ENG FOUND NO LEAKS AND HYD PRESSURE WAS NORMAL, 3000 PSI, THEN MADE A WRITE-UP FOR THE NEXT SHIFT TO RUN ENG FOR 5 MINS AND CHK FOR LEAKS. THIS HAPPENED JAN/TUE/02, AND ON JAN/WED/02, ACFT TOOK OFF AND COULD NOT RETRACT R-HAND GEAR DOOR. SO RETURNED TO FIELD. THEN I HAPPENED TO PICK ACFT UP AT GATE AND TOWED TO MAINT. FOUND #4 HYD SYS WITH ADP ON WAS AT 2600 PSI AFTER 15 MINS OF RUNNING WAS AT 1500 PSI ON JAN/THU/02. ANOTHER GROUP OF MECHS FOUND CONTAMINATION AND THAT ONE OF THE SUPPLY LINES WAS CLOGGED INSIDE. THIS WAS ON JAN/THU/02. SUPPLEMENTAL INFO FROM ACN 536044: DURING REPLACEMENT OF #4 EDP PER MAINT MANUAL 29-11-05, WE NOTICED NO DISCOLORATION OR ABNORMAL SMELL OF SKYDROL. WE NOTICED NO BLOCKAGE OF SLUDGE IN THE LINES. I FELT THAT MAINT MANUALS WERE CONTRADICTING AND NOT SPECIFIC CONCERNING SPECIFIC PROBS.

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.