Narrative:

Prior to takeoff while holding in blocks, facing 270 degrees (winds out of 180 degrees and gusting), another aircraft informed us fuel leaking from left wing. Captain and flight engineer checked and ascertained that with full fuel in left tank and increased temperature since fueling, some fuel (in small quantity) leaking from vent and running inboard not unusual for large transport. All hydraulic pressures and quantity normal. About 40-45 mins after takeoff and almost level at 31000 ft, we lost B system hydraulics. Performed all appropriate checklists and eventually diverted to phl due to WX in ewr and extensive holding. Our perception of situation prior to takeoff was of a normal leak of overflow fuel. In retrospect, it was probably the small beginning of a hydraulic leak. We, as a crew, used our best judgement and checked all system to be normal prior to takeoff. We decided all system to be normal and to continue the flight. Supplemental information from acn 239353: post-flight inspection revealed the leak came from a blown o- ring in a left wing spoiler actuator.

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Original NASA ASRS Text

Title: AN ACR LGT HAD A HYD SYS FAILURE. IT WAS NOTICED ON THE GND BY ANOTHER ACFT.

Narrative: PRIOR TO TKOF WHILE HOLDING IN BLOCKS, FACING 270 DEGS (WINDS OUT OF 180 DEGS AND GUSTING), ANOTHER ACFT INFORMED US FUEL LEAKING FROM L WING. CAPT AND FE CHKED AND ASCERTAINED THAT WITH FULL FUEL IN L TANK AND INCREASED TEMP SINCE FUELING, SOME FUEL (IN SMALL QUANTITY) LEAKING FROM VENT AND RUNNING INBOARD NOT UNUSUAL FOR LGT. ALL HYD PRESSURES AND QUANTITY NORMAL. ABOUT 40-45 MINS AFTER TKOF AND ALMOST LEVEL AT 31000 FT, WE LOST B SYS HYDS. PERFORMED ALL APPROPRIATE CHKLISTS AND EVENTUALLY DIVERTED TO PHL DUE TO WX IN EWR AND EXTENSIVE HOLDING. OUR PERCEPTION OF SIT PRIOR TO TKOF WAS OF A NORMAL LEAK OF OVERFLOW FUEL. IN RETROSPECT, IT WAS PROBABLY THE SMALL BEGINNING OF A HYD LEAK. WE, AS A CREW, USED OUR BEST JUDGEMENT AND CHKED ALL SYS TO BE NORMAL PRIOR TO TKOF. WE DECIDED ALL SYS TO BE NORMAL AND TO CONTINUE THE FLT. SUPPLEMENTAL INFO FROM ACN 239353: POST-FLT INSPECTION REVEALED THE LEAK CAME FROM A BLOWN O- RING IN A L WING SPOILER ACTUATOR.

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.