B777 Captain reported low engine oil quantity during cruise. The flight crew shut down the engine; diverted to an alternate airport and landed safely.

Narrative

To be clear. I was the relief captain; but was in command of the jet while the flying captain was on break when the engine was shut down. We were told by dispatch while still at the hotel that the jet was ready for us once we got to the airport. The limo dropped us off at ZZZZ and there was no one there to meet us. We called dispatch and they said someone would be right over; which took about 20 minutes. Person A met us; I'm not sure who the man was; but said they were still working on the jet as they had done a high power test on the jet (this was a Maintenance ferry flight for the aircraft ZZZZ-ZZZ due to a left engine change) and there was a prob with the a valve of some sort on the engine. We were told to wait outside security for an hour and he would come back at XA:00 with an update on the progress. The drop dead Critical Crew Offtime (CCO) time was XC:40. The four of us (2 Captains and 2 First Officers) went to a restaurant and waited for an hour; and around XB:15 we were given an escort who took us through security and customs to a parking stand where the aircraft was waiting. We went through the ferry flight checklist and conducted all the necessary items to get ready for departure. Once we were ready the aircraft was closed up but there was an issue with the mobile jet bridge. It would not start and it took 15-20 minutes for the ground crew to tow the jet bridge away from the jet. We taxied out but were unable to make the CCO time; so we taxied back and shut down and waited to get a new flight plan to go ZZZZ-ZZZ1. That took about an hour and we taxied for takeoff and then what happened after is covered in the following details; which was the report jointly written by myself and the flying captain. My portion of the report written in 3rd person. I am Person DZZZZ-ZZZ1 and subsequent diversion to ZZZZ1This was a maintenance ferry from ZZZZ-ZZZ1. Aircraft 777-300ER had a left engine change performed at ZZZZ. Takeoff (at XB:44) and level off was uneventful with the Flying Captain (Person B) and Flying FO (Person C) at the controls and Relief Captain (Person D) and Relief FO (Person E) in the observer seats. The Relief Pilots went to the bunk passing FL180 and the flying pilots conducted a ETOPS verification and sent the code to MX. At XG:16 the Relief Pilots took over and the flyers went to the bunk. At XG:27 the Relief Pilots notified Maintenance Control via ACARS that the L Engine Oil quantity was at 2 quarts. They flowed up at XG:31 after no response; with a reminder to Maintenance Control that this was the new motor. The response from Maintenance Control was 'Capt; So Im clear the left engine is indicating only 2 qts NOW?' Upon receiving this; Person D gave control of the aircraft to Person E and called Dispatch/Maintenance Control on SATCOM to confer and the result was to continue on the route and monitor the Oil Pressure and Oil Temperature. At that time the L and R oil pressures were around the same at approx 58psi. Within 10 mins after the call to Maintenance Control; the Left Engine Oil Pressure began to slowly decrease at the rate of about 1PSI every 10 minutes. Dispatch and Maintenance were called again to notify them that the Oil Pressure had dropped to 45PSI with fluctuations to 43PSI. At that time the jet was now past the CP Person D had slowed the Aircraft down to keep us on the ZZZZ2 side to try and avoid the ZZZZ3 side) Person D and Person E conferred with Dispatch and Maintenance Control agreed and decided the best action was to head to ZZZZ1. Person D told Dispatch to stay on the line with Person E while he went back to confer with Person B who was in the bunk sleeping. Person B agreed with Person D and Person D went back to the cockpit and told Dispatch and Maintenance Control; the Aircraft would be conducting a precautionary diversion to ZZZZ1.The relief crew notified ZZZZ [ARTCC] via CPDLC of the need to divert. With no answer; the relief crew called ZZZZ [ARTCC] on HF and got an initial clearance and a descent from the Block FL 350-360 to a hard FL 350. Person E reprogrammed the FMC and Person D started a left turn and descended to FL 350 and turned all the exterior lights on until on a direct heading to the new waypoint. The remainder of the clearance came via CPDLC. At XH:19 ZZZZ [ARTCC] requested the reason for the divert and the relief crew responded with 'precautionary divert due to left engine oil issues'. The Diversion procedures in both the FOM and FM (Flight Manual) were reviewed and the Chief Pilot was contacted via ACARS and advised to contact dispatch for an update on our diversion. The oil pressure continued to decrease to 25PSI (changing from white to amber numbers) at approx XI:00At XI:25 Dispatch/ Maintenance Control was contacted to find out when the caution would come on for low oil pressure; as it had now dropped to 18PSI. The relief crew contacted ZZZZ [ARTCC] for a block FL280-350 (which was denied) to set up a preemptive single engine cruising altitude. (the rate of decrease of Oil pressure as time elapsed; indicated the crew would need to shut down the affected engine.) The relief crew also preemptively ran through the Low Oil Pressure L checklist to see what was coming. As stated previously; the oil pressure dropped about 1 PSI every 10 minutes and it became apparent the relief crew would have to shut the engine down. In anticipation they asked for a descent to the engine out altitude of FL280. At 10 PSI the low oil pressure caution came on and Person D called Person B in the bunk and told him to come to the cockpit and handed the jet over to Person E and ran the Low Oil Pressure L checklist. The Relief Crew also ran the QRC driftdown procedure; without having to turn off course. Person B and Person C came back on duty; well rested and took their respective seats after an extensive turnover of all events/reports etc. The flying crew requested FL 240 and flew for 30 minutes at that altitude coordinating with dispatch and ATC for our arrival runway of XXR. The entire crew; under the leadership of Person B (and Person D in his absence ); used CRM and went through the many options available and elected on a Flaps 20; max auto brakes; ILS to XXR with a wet [runway] and winds XXX/15. The flying captain did an excellent job and landed safely in the touchdown zone. As requested by the Captain; the ground crew was waiting ready for any potential safety problems. Captain [Person B's] input: Crew was scheduled to do a maintenance ferry flight from ZZZZ-ZZZ. Upon arrival at the airport we were advised by station personnel that there were some open log items to be completed but they were aware that the crew had a limited time before we would go illegal for the length of the flight. After an hour they escorted the crew to the aircraft we completed the normal preflight duties and taxied to the runway. Unfortunately as we approached the runway we missed our CCO time. We were rescheduled to fly the aircraft to ZZZ1. Taxi out and departure were uneventful. During the climb the relief crew; Captain [Person D] and FO [Person E]; went back for their XX:10 break. During cruise FO [Person C] and I performed normal ETOPS operational items including a required ETOPS maintenance verification on the left engine; which had just been replaced. During cruise I cycled through the system pages a couple times but noted no issues with the new engine. The relief pilots took over with a normal transition brief and myself and FO [Person C] went on our break. Approximately; an hour into our rest Captain [Person D] woke me up to advise me the left engine was losing oil quantity and oil pressure. He had been conferring with dispatch and Maintenance Control and we discussed a precautionary return to ZZZZ1 while the engine was still in an operational state. All parties agreed and Captain [Person D] and FO [Person E] orchestrated the process to begin our return to ZZZZ1. After assuring the situation was stable I went back to my break so I would be well rested for the approach and landing should we need to shut the engine down prior to our landing. Approximately an hour later Captain [Person D] called the bunk and advised me that they were going to have to shut down the left engine. At this point myself and FO [Person C] returned to the cockpit. We transitioned into control seats after being briefed on the situation. Dispatch; Maintenance Control and ATC had already been advised. As a crew we all worked together to make sure all contingencies and appropriate checklists had been accomplished. We picked the longest runway available and had dispatch confirm landing distance for our conditions. The approach was briefed and ATC was advised. We did not require fuel jettison. ATC vectored us and cleared us for the requested ILS to XXR. As the PF I had the autopilot fly down to approximately 400'. The landing was uneventful; we cleared runway and taxied to our hardstand without incident. After arrival I made all the required verbal notifications to dispatch and the Chief Pilot.