Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 33.88; Flight Crew Total 8480.20; Flight Crew Type 4074.10
Situational Awareness; Communication Breakdown; Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
This flight was an OE [Operating Experience] with a New Hire FO [First Officer]; and double augmented crew. Normal briefings and departure preparations. Normal takeoff and climb out.I was on break at in the cabin with FO NAME (OE student). Approaching W040 at approximately XA:15 Z I was notified by one of the FAs [Flight Attendants] that I was needed on the Flight Deck.  When I arrived there; FO NAME and NAME1 told me that the 'L HYD QTY' EICAS had appeared and that they were working the HYD QTY - L (C; R) (FM 2.130.4) checklist. At that time the left hydraulic quantity was at .48 and while we were watching it dropped to .47. In accordance with the checklist; we turned off the left hydraulic pumps.We then contacted and consulted with Dispatch and Maintenance Control and made an ELB entry. Dispatch advised that the weather and winds were forecast to be favorable for our arrival in ZZZ. Dispatch said that they would contact ZZZ and advise them of the situation. Maintenance Control advised that it was likely a slow leak and that the checklist offered the best advice for the situation. After the checklist and all coordination was complete; I returned to the cabin to continue my rest. I chose not to wake FO NAME2 and to allow him to continue his rest uninterrupted so that he would be alert as PF.About 30 minutes later at XB:08 a FA woke me again and said that I was needed on the Flight Deck again. When I arrived; I was advised that the R YAW DAMPER EICAS had appeared. We completed the YAW DAMPER - L (R) (FM2.90.46) and made another ELB entry. We researched and found that the hydraulic power source for the right yaw damper is the left hydraulic system that we had just depressurized. We concluded that they were likely related. We advised Dispatch and made another ELB entry. I returned to the cabin to complete my rest period.During the approach briefing we calculated the landing distance for a normal landing; and one for the loss of the left hydraulic system. We were concerned that when we turned the pumps back on during the approach that we might lose the left system quantity completely. We initially planned to configure early for the approach; but on reflection decided to configure normally and then turn the pumps back on when fully configured. If we lost the remaining quantity at that time; we were prepared to reconfigure for a flaps 20 landing. It was agreed that FO NAME2 would make the landing if the system quantity held and that I would make the landing if it did not.On approach we turned the pumps back on after we were fully configured for landing. The pressure came up on the system and quantity held for the rest of the flight. The landing was normal and uneventful. ZZZ had CFR available for our arrival and a tug if it was needed to help us clear the runway.The cabin crew were aware of the situation; but we advised them it would be a normal operation. We choose not to advise the passengers as we fully anticipated a normal landing.One concern arose during the event. During the calculation of the landing distance there was some confusion on which line to use on the chart. With a potential loss of the L HYD system it was unclear if we were to use the line for HYD SYS PRESS L ONLY or HYD SYS PRESS R and C. The title of the column says Aircraft Config/Condition and that does not clarify which row to use. To be safe we calculated both and found that we had ample runway in either case. But it brings up the question does the row titled HYD SYS PRESS L ONLY mean that you 'only' have the left system and the other two are failed; or does it mean that 'only' the left system has failed? After looking at the landing distances; I believe the right row was indeed HYD SYS PRESS L ONLY. But it might be worth a look at this chart for crews who are managing a more critical landing distance issue without the time we had to study it.All the crew did an exceptional job during this event. FOs NAME; NAME1; and NAME2 in particular were exceptional in their handling of the event.
Captain reported loss of left hydraulic system that also caused the right hand yaw damper to fail.  The flight crew performed the required tasks and continued the flight to destination airport.