B777 flight crew reported engine oil pressure and quantity fluctuations during cruise resulted in a diversion.
Synopsis
B777 flight crew reported engine oil pressure and quantity fluctuations during cruise resulted in a diversion.
Narrative
At cruise altitude L ENG oil QTY decreased to 4 quarts initially and we established 1st of 4 SATCOM calls with Dispatch; Maintenance Control; Chief Pilot; and I had engineering looped in for advice over a 3+ hour time period. Initially L ENG psi was 58. Continuous slow deterioration and eventual fluctuation of L ENG psi and oil QTY (quarts) lead to divert to ZZZ. It was the Maintenance Control assessment the engine probably would not continue to operate all the way to ZZZ1. Largest factor in the decision was the continuous deterioration of the L ENG psi combined with fluctuations and low oil QTY and engine history lead to conclusion. Maintenance attempted to solve why this L ENG had been losing or burning oil on previous flights and unable to resolve. Person A est psi was 23 on L ENG after divert was initiated to ZZZ. Engine never had to be shut down. 2+15 to ZZZ once the divert decision was made. More than 4 hours remained to ZZZ1. Priority handling was requested with ATC; SATCOM call made to Center and CPDLC to ZZZ received. Fuel jettison was not needed. Landed 2;000 lbs under Max Structural Landing Weight. Outstanding flight deck and cabin crew support and professionalism from dispatch and all team members. Successful safe outcome.
Second reporter narrative
While enroute; cruise; FL340; between longitude XX and XY; we noticed left oil quantity had decreased to 4 qts. Pressure was slightly lower than the right side; by about 3-6 psi. We initiated contact with dispatch and Maintenance Control and reviewed engine oil systems in the Flight Manual (FM). They said there were 'many' more quarts in the system and it shouldn't be an issue as long as the pressure didn't decrease substantially; but to monitor quantity and pressure trends and keep them in the loop. Maintenance Control noted this engine had had a history of very high oil burn. At that time; the relief crew came up as scheduled; and I started my rest break. Approx 2 1/2 hours later; they called me up to the flight deck as the oil quantity gauge had decreased to 1 and the pressure had slowly been decreasing to the low 50s; well below the 68ish on the right engine. The pilots had had numerous conversations at that point with Maintenance Control; dispatch; Chief Pilot and engineering and the consensus was that there was no way to be confident the motor would keep running if we continued to ZZZ1. Also; 10 psi was the minimum before we would get an EICAS and likely shut the engine down. We were concerned retarding the engine to idle upon descent could have reduced the oil pressure to below 10 psi. The consensus amongst the pilots and the support team was that a divert to ZZZ was the appropriate and prudent solution. We then notified Center of the need to divert to ZZZ and requested priority handling. During the divert; we previewed the ENG OIL PRESS L and single engine landing/go around/approach checklists and ran through every possible contingency scenario we could think of during our divert. We would be above max landing weight for ZZZ. The engine oil pressure stayed above 10 psi and we flew an uneventful approach and landing.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.