Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
At cruise; pilots noticed oil quantity declining in left engine. When it got to 8 quarts; they pulled left throttle to idle; turned around; descended and headed back to ZZZ. [Left] engine remained at idle and oil quantity remained at 8 quarts for the remainder of the flight. [The cause was a] high pressure oil component leaked.
B787 First Officer reported loss of left engine oil quantity; resulting in a return to departure airport.