Narrative:

While in cruise on [airway]; we got a hydraulic qty low 1 EICAS (engine indication and crew alerting system) message. We ran the checklist. At this time we had normal pressure in all hydraulic (hydraulic) systems. I believe the system 1 quantity at this time was approximately .23. It steadily decreased before our very eyes; with the pressure holding. I contacted dispatch on the sat (satellite) phone; who patched in mx (maintenance) control. Mx control recommended continuing to ZZZ; and keep an eye on it. We figured we were going to lose the pressure when we started with the flaps and gear; but that could happen in one hour; or in 8. We agreed to keep an eye on it. Further along; we step climbed from 310 to 330. Upon movement of the elevator to climb; the hydraulic system pressure 1 dropped briefly; then came back up. We leveled off; then shortly thereafter; the pressure bottomed out; and we got the hydraulic press system 1 EICAS message. We ran that checklist. Concurrently; the quantity on system 4 dropped from .9; to .63. Again I called dispatch; and mx control. I asked if there was a reason system 4 should be dropping; while in cruise. They had no definitive answer. At this time I determined it wasn't prudent to cross the pacific. Between dispatch; mx; [maintenance operations manager]; and whoever else; we made the decision to divert into ZZZZ. We advised ATC) of such; and that we needed to dump fuel for approximately 45 minutes. We developed an arrival plan; dumped approximately 50.0 fuel; and proceeded inbound to land. I had dispatch advise ZZZZ we would be needing a tug; due to no nose wheel steering; and I advised ATC of such; also. I had ZZZZ have the emergency equipment standby as a precaution; but declined to declare an emergency; unless further issues dictated. We made an uneventful arrival/approach/landing. I was able to taxi clear of the runway using a combination of a/south steering effectiveness; differential braking/power; and a convenient taxiway. We stopped; shut down; and were towed into the gate. Mx advised that there was a major hydraulic leak coming from the tail. [Both first officers] did an excellent job throughout this event; as did the dispatcher; mx (maintenance) control; and whoever else participated behind the scenes. There was good communication between myself and dispatch; mx control; and operations personnel. We had an initial plan; then when circumstances dictated; we adjusted the plan; and executed it. Communication between all concerned was excellent; and that showed in the end result. I let it be known to the crew that we had gas (plenty of gas); and presently; we had time. So we will be slow; deliberate; and make sure we cross all the t's; and dot all the i's; in all phases of what we were doing. First officer's did an excellent job; and to me were an excellent reflection on the job that the training center does. It all went like it was supposed to.

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Original NASA ASRS Text

Title: B747-400 flight crew encountered a hydraulic leak and diverted.

Narrative: While in cruise on [airway]; we got a HYD QTY LOW 1 EICAS (Engine Indication And Crew Alerting System) message. We ran the checklist. At this time we had normal pressure in all HYD (Hydraulic) systems. I believe the system 1 quantity at this time was approximately .23. It steadily decreased before our very eyes; with the pressure holding. I contacted Dispatch on the SAT (Satellite) phone; who patched in MX (Maintenance) Control. MX Control recommended continuing to ZZZ; and keep an eye on it. We figured we were going to lose the pressure when we started with the flaps and gear; but that could happen in one hour; or in 8. We agreed to keep an eye on it. Further along; we step climbed from 310 to 330. Upon movement of the elevator to climb; the HYD SYS pressure 1 dropped briefly; then came back up. We leveled off; then shortly thereafter; the pressure bottomed out; and we got the HYD PRESS SYS 1 EICAS message. We ran that checklist. Concurrently; the quantity on SYS 4 dropped from .9; to .63. Again I called Dispatch; and MX Control. I asked if there was a reason system 4 should be dropping; while in cruise. They had no definitive answer. At this time I determined it wasn't prudent to cross the Pacific. Between Dispatch; MX; [Maintenance Operations Manager]; and whoever else; we made the decision to divert into ZZZZ. We advised ATC) of such; and that we needed to dump fuel for approximately 45 minutes. We developed an arrival plan; dumped approximately 50.0 fuel; and proceeded inbound to land. I had Dispatch advise ZZZZ we would be needing a tug; due to no nose wheel steering; and I advised ATC of such; also. I had ZZZZ have the emergency equipment standby as a precaution; but declined to declare an emergency; unless further issues dictated. We made an uneventful arrival/approach/landing. I was able to taxi clear of the runway using a combination of A/S steering effectiveness; differential braking/power; and a convenient taxiway. We stopped; shut down; and were towed into the gate. MX advised that there was a major hydraulic leak coming from the tail. [Both First Officers] did an excellent job throughout this event; as did the Dispatcher; MX (Maintenance) Control; and whoever else participated behind the scenes. There was good communication between myself and Dispatch; MX Control; and Operations personnel. We had an initial plan; then when circumstances dictated; we adjusted the plan; and executed it. Communication between all concerned was excellent; and that showed in the end result. I let it be known to the crew that we had gas (plenty of gas); and presently; we had time. So we will be slow; deliberate; and make sure we cross all the t's; and dot all the i's; in all phases of what we were doing. FO's did an excellent job; and to me were an excellent reflection on the job that the training center does. It all went like it was supposed to.

Data retrieved from NASA's ASRS site 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.