Narrative:

During taxi out the first officer pointed out that the center hydraulic system quantity was near RF level. Since it was within limit we continued and took off. After reaching climb we checked the level again and it was at 90 which was a good bit more than we had read during taxi. We continued to monitor the center hydraulic quantity but noticed as we neared the east coast of canada prior to entering atlantic ETOPS that the level was dropping. We noted that it was decreasing at a rate of about .01 per 7 mins of flying. By this time the level had dropped to below RF and continued to drop. I first sent an ACARS note to ZZZZ maintenance about the observation and asked for an opinion. I got no response from them. Once we confirmed the level continued to drop I made a satcom call to dispatch and had maintenance control patch on. We had a discussion as to how to proceed but I continued to see the quantity drop and quickly made a decision to return to the united states. We followed the flight manual procedure for C hydraulic quantity EICAS even though we had not reached the .50 level. I saw that within time we would reach that level anyway. The procedure led us to turn off the center pumps to preserve what fluid we had and turn them back on during approach to land. I made a decision to divert to ZZZ as it is a maintenance station and seemed closest airport for us with good facilities. It was about 1 hour 30 mins to ZZZ. During this time we briefed the cabin purser and had them use a cabin advisory. We also reviewed the checklist for C hydraulic pressure lights in case we got into that situation. At this point I was a bit disappointed with our maintenance department because we tried to reach them to ask at what level of quantity would we expect to lose pressure and be in that situation. Maintenance control could not connect us to the B767 controller and only a B737 controller could speak to us so we did not get good information back. As we descended into ZZZ at about FL200 as the first officer followed the approach descent check we then got the C hydraulic pressure EICAS message. We immediately declared an emergency; asked for emergency equipment in ZZZ and to land into the wind with the longest runway. I had the first officer fly while I ran the C hydraulic pressure loss checklist up to the point of putting the gear down. I then took command of flying and had the other 2 first officer's finish the list. It worked better that way to fly the approach more normally. We had to lower the gear with alternate method; lower the flaps with alternate flaps switches and land flaps 20 degrees. The landing progressed normally and we were able to exit the runway at the end and taxi under our own control at the gate. ZZZ maintenance found a pin hole had ruptured the hydraulic line from the stabilizer trim. It was repaired in ZZZ and we ferried the aircraft back to ZZZ1 the next day.

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Original NASA ASRS Text

Title: B767 FLT CREW REPORTS CENTER HYDRAULIC LEAK IN THE STABILIZER TRIM LINE. THE PRESSURE LOSS REQUIRED ALTERNATE METHODS OF FLAP AND GEAR EXTENSION AT DIVERT ARPT.

Narrative: DURING TAXI OUT THE FO POINTED OUT THAT THE CTR HYD SYS QUANTITY WAS NEAR RF LEVEL. SINCE IT WAS WITHIN LIMIT WE CONTINUED AND TOOK OFF. AFTER REACHING CLB WE CHKED THE LEVEL AGAIN AND IT WAS AT 90 WHICH WAS A GOOD BIT MORE THAN WE HAD READ DURING TAXI. WE CONTINUED TO MONITOR THE CTR HYD QUANTITY BUT NOTICED AS WE NEARED THE EAST COAST OF CANADA PRIOR TO ENTERING ATLANTIC ETOPS THAT THE LEVEL WAS DROPPING. WE NOTED THAT IT WAS DECREASING AT A RATE OF ABOUT .01 PER 7 MINS OF FLYING. BY THIS TIME THE LEVEL HAD DROPPED TO BELOW RF AND CONTINUED TO DROP. I FIRST SENT AN ACARS NOTE TO ZZZZ MAINT ABOUT THE OBSERVATION AND ASKED FOR AN OPINION. I GOT NO RESPONSE FROM THEM. ONCE WE CONFIRMED THE LEVEL CONTINUED TO DROP I MADE A SATCOM CALL TO DISPATCH AND HAD MAINT CTL PATCH ON. WE HAD A DISCUSSION AS TO HOW TO PROCEED BUT I CONTINUED TO SEE THE QUANTITY DROP AND QUICKLY MADE A DECISION TO RETURN TO THE UNITED STATES. WE FOLLOWED THE FLT MANUAL PROC FOR C HYD QUANTITY EICAS EVEN THOUGH WE HAD NOT REACHED THE .50 LEVEL. I SAW THAT WITHIN TIME WE WOULD REACH THAT LEVEL ANYWAY. THE PROC LED US TO TURN OFF THE CTR PUMPS TO PRESERVE WHAT FLUID WE HAD AND TURN THEM BACK ON DURING APCH TO LAND. I MADE A DECISION TO DIVERT TO ZZZ AS IT IS A MAINT STATION AND SEEMED CLOSEST ARPT FOR US WITH GOOD FACILITIES. IT WAS ABOUT 1 HR 30 MINS TO ZZZ. DURING THIS TIME WE BRIEFED THE CABIN PURSER AND HAD THEM USE A CABIN ADVISORY. WE ALSO REVIEWED THE CHKLIST FOR C HYD PRESSURE LIGHTS IN CASE WE GOT INTO THAT SIT. AT THIS POINT I WAS A BIT DISAPPOINTED WITH OUR MAINT DEPT BECAUSE WE TRIED TO REACH THEM TO ASK AT WHAT LEVEL OF QUANTITY WOULD WE EXPECT TO LOSE PRESSURE AND BE IN THAT SIT. MAINT CTL COULD NOT CONNECT US TO THE B767 CTLR AND ONLY A B737 CTLR COULD SPEAK TO US SO WE DID NOT GET GOOD INFO BACK. AS WE DSNDED INTO ZZZ AT ABOUT FL200 AS THE FO FOLLOWED THE APCH DSCNT CHK WE THEN GOT THE C HYD PRESSURE EICAS MESSAGE. WE IMMEDIATELY DECLARED AN EMER; ASKED FOR EMER EQUIP IN ZZZ AND TO LAND INTO THE WIND WITH THE LONGEST RWY. I HAD THE FO FLY WHILE I RAN THE C HYD PRESSURE LOSS CHKLIST UP TO THE POINT OF PUTTING THE GEAR DOWN. I THEN TOOK COMMAND OF FLYING AND HAD THE OTHER 2 FO'S FINISH THE LIST. IT WORKED BETTER THAT WAY TO FLY THE APCH MORE NORMALLY. WE HAD TO LOWER THE GEAR WITH ALTERNATE METHOD; LOWER THE FLAPS WITH ALTERNATE FLAPS SWITCHES AND LAND FLAPS 20 DEGS. THE LNDG PROGRESSED NORMALLY AND WE WERE ABLE TO EXIT THE RWY AT THE END AND TAXI UNDER OUR OWN CTL AT THE GATE. ZZZ MAINT FOUND A PIN HOLE HAD RUPTURED THE HYD LINE FROM THE STABILIZER TRIM. IT WAS REPAIRED IN ZZZ AND WE FERRIED THE ACFT BACK TO ZZZ1 THE NEXT DAY.

Data retrieved from NASA's ASRS site as of May 2009 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.