Date: 201807
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B767 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Hydraulic System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness; Troubleshooting
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Contributing factors: Airspace Structure; Aircraft
Primary problem: Aircraft

Narrative: I was the Captain. Preflight preparation; push-back; start-up and taxi out were uneventful. We took off on runway XX with a flaps 5 setting. Climb out to FL340 was also uneventful. Approximately 40 minutes after takeoff we got a C HYD QTY EICAS message. We pulled up the status page and noticed that the Center hydraulic quantity was at .43 and decreasing rapidly. The First Officer pulled out the QRH and iPad and referenced the procedures for this anomaly. The Center pumps; both electric and the demand pumps were secured. This slowed the quantity decrease; but did not stop it. I initiated a SATCOM call to Dispatch and was eventually conferenced in with [Maintenance]; the [Operations] and the 756 fleet guys. A detailed discussion ensued covering all implications of continuing the flight or turning around and returning to ZZZZ or another suitable divert aerodrome. The divert option was eventually ruled out as it would involve fuel dumping (13000 available to dump) and at least two hours of loitering to burn down to max landing weight for the 767-300. My concerns about the legality of continuing an ETOPS flight without the Center system and associated loss of our HMG (Hydraulic Motor Generator) were assuaged and we collectively (internal flight crew and external resources) decided to continue the crossing. The flight proceeded normally until approaching ZZZ. I was on third break and returned to the cockpit approximately 50 minutes before scheduled landing. The Center system quantity at this point was .11. The three of us discussed all possible scenarios again and we began our descent. When we checked in with Approach; we [advised ATC] and requested the ILS to XXR so as not to interrupt normal operations on the center and left runways. This also gave us potential maneuvering airspace on the less congested side of the airport.At 6000 ft. and about 35 miles from the approach end of XXR; we ran the checklist items. We were reasonably certain that the Center system would not work due to the 'spoiler' EICAS when I deployed speed brakes on the descent. When the demand pump was turned on; the Center pressure lights remained on; so we continued the applicable checklist. We had slowed to 220 knots clean maneuvering and began to bring the flaps down via the alternate method. As the flaps transited from 0 to 1; we got a LE SLATS ASYMMETRY EICAS and the flaps stopped moving. We were now around 22 miles from the runway and still at 220 knots. We informed tower that we might have to execute a 360 degree turn to work the additional emergency of split slats. We had also lost the Left Yaw damper earlier in the flight. The relief pilot was working the LE slats problem while we continued the alternate flap problem. I called for the alternate gear extension at some point in this process and the gear came down and locked as advertised. I asked the PM (Pilot Monitoring) to select flaps 5 on the alternate switch and around 12 miles from touchdown; the flaps began to move again; but still with the asymmetry indication. I asked the relief pilot if that was going to be a problem and he said 'not if the flaps come down.' We continued to dial the speed back as the flaps came down and after almost 6 minutes from alternate flap initiation and at approximately 8-10 miles; we got the aircraft at flaps 20 and target speed 150 (ref 144 + 6 knots for the wind {120/12}).I disengaged the auto flight at 1500 ft. and flew a normal approach to touch down on XXR. We exited the runway and with the Reserve Steering and Brakes switch engaged had enough standpipe pressure to clear the runway using nose wheel steering. Emergency responders were there immediately and confirmed that we still had hydraulic fluid leaking from the port wheel well area and we soon had zero Center quantity as the remaining fluid leaked out. A tug eventually came and towed us to [our] gate. I would like to say that this was a textbook collaboration of resources; both internal (cockpit and cabin) and external. We worked as a team and resolved what could have been a serious emergency. I kept the pursuer engaged from soon after the caution light until after landing. I did not ask that the cabin be prepared for evacuation; due to the nature of the problem and only an extra 8-10 knot approach speed expected. Although I didn't use the term 'Cabin Advisory'; the words I used when briefing her were reflective of that process. Tip of the hat to all involved and 220 souls on board were happy to have landed safely.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B767 flight crew reported a hydraulic leak that developed inflight worsened inflight causing an Asymmetrical flap and slat problem as well as the loss of the left yaw dampener and primary steering upon landing.