B757-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Landed in Emergency Condition
Aircraft
At Cruise after departing the track shortly after the Captain (CA) began her rest break; we got a L HYD QTY status message and the L RSVR light illuminated.  We were down to .41 with RF showing on the left system with good pressure.  C and R systems were normal and remained so for the remainder of the flight.  The First Officer (FO) and I consulted the QRH and as time went on we determined we were slowly loosing quantity.  We evaluated our position and weather and had multiple choices if needed.  We both believed that we would eventually end up with a complete loss of the left hydraulic system.  We called the CA back to the flight deck.  We briefed the CA on the failure and discussed the many issues involved with the impending loss of the left HYD system.  We contacted dispatch and maintenance on SAT and eventually decided to continue to destination.  The L system quantity continued to decrease and eventually (still at cruise) we got a L HYD ENG PUMP and PRESS.  We turned off the L ENG HYD PUMP as per the QRH.  We reviewed the HYDRAULIC SYSTEM PRESSURE (L only) QRH procedure and were prepared for the long checklist to configure the aircraft for landing using the alternate flap and gear extension and were prepared for all the associated losses to aircraft performance and stopping capabilities.  We coordinated with approach and arrival for a long slow final to configure the aircraft and as expected; when we went for Flaps 1 we got the L SYS PRESS light.  We ran the QRH procedure and configured as per the QRH and landed.  The FO landed and the CA was able to clear the runway.  We shut down and were towed to the gate.
Left Hydraulic System Leak; I was the pilot monitoring and while on my rest break the flight attendant came and got me to tell me that the co-pilots wanted me back on the flight deck. When I arrived on the flight deck I was briefed that they had gotten a L HYD QTY EICAS message with an Amber RSVR light on the overhead panel. They accomplished the QRH procedure which was simply a 'condition' statement that the hydraulic quantity was low. The Left HYD QTY on the EICAS showed .41 with an RF symbol and normal pressure. In the time they briefed me the quantity was continuing to decrease. I placed a call to dispatch and advised them of our situation; they in turn put us through to maintenance. He had a copy of our QRH and was reading the procedures. His response to us was that he felt it was not a very good checklist. We all agreed that the most likely scenario would be that we would eventually lose the Left Hydraulic System and he suggested we turn off the Left HYD Engine pump and Left HYD Electric pump. I told him that I would not go outside the box and turn off pumps until the EICAS warnings were present and the QRH called for the procedure. He understood and agreed. After discussing our options with dispatch we agreed to continue on to destination. The weather was good there; the field had long runways available with favorable winds. We were preparing ourselves for a complete loss of the Left Hydraulic System which would leave us with Alternate Flap Extension; Alternate Gear Extension; Manual Speedbrake Extension; Left Thrust Reverser Inoperative (Inop); some Spoilers Inop and Rudder Ratio Inop.The Left Hydraulic Quantity eventually dropped to .18 and fluctuated lower to .14-.12. System pressure started to fluctuate and we got a L HYD ENG PUMP EICAS message with an Amber PRESS light on the overhead panel. We followed the QRH and turned the Eng HYD Pump OFF. We requested priority handling for a long and slow final for the longest runway.Descent was normal and we got vectors for the ILS. When Slats were extended we got the L HYD SYS PRESS EICAS MSG and the amber overhead SYS PRESS light. We continued with the QRH procedure. The [relief officer] and I working the checklist and the first officer flying and communicating. We alternately extended the flaps and gear and advised ATC that there was a possibility that we would not be able to clear the runway due to loss of nose wheel steering. The landing was normal and I was able to clear the runway. Once clear Airport Rescue and Fire Fighting (ARFF) assessed the condition of the aircraft and landing gear. ARFF reported the aircraft was normal and ground personnel could approach. We shut down the engines and waited for maintenance to tow us to the gate. The tow to the gate was normal and uneventful.
A B757 flight crew experienced low fluid quantity in the left hydraulic system about two hours from destination and elected to continue. Before leaving cruise altitude the fluid was depleted and pressure was lost. Alternate gear and flap extension QRH procedures were used and a normal landing ensued.