A B777 LOST OIL QTY ON AN OCEANIC TRACK AND DIVERTED TO A NEARBY ARPT. AN EMER WAS DECLARE BUT THE ENG REMAINED RUNNING UNTIL LNDG.

Narrative

APPROX 3 HRS INTO THE FLT; OIL QUANTITY IN THE L ENG DECREASED 3 QUARTS. AFTER DISCUSSING IT; WE DECIDED TO INITIATE A DIVERSION AND TRY TO RETURN TO ZZZ. WE WERE UNABLE TO OBTAIN A CLRNC FROM ZZZ CTR WHILE AT FL370 AND ON OUR ASSIGNED TRACK; THEREFORE; FOLLOWING FLT MANUAL GUIDANCE; WE DECLARED AN EMER; OFFSET 15 NM N OF TRACK AND DSNDED TO FL310 SO THAT WE COULD OBTAIN SUCH CLRNC. OUR INITIAL INTENT WAS TO TRY TO FLY TO ZZZ SINCE OIL QUANTITY WAS HOLDING STEADY AT 3 QUARTS AND ALL OTHER ENG INDICATIONS WERE NORMAL. CONTACTED DISPATCH AND ESTABLISHED A 3 WAY PHONE PATCH WITH MAINT CTL WHO AGREED THAT OUR SITUATION MOST LIKELY WAS AN OIL QUANTITY ISSUE INSTEAD OF JUST A BAD INDICATION SINCE THE FUEL OIL HEAT EXCHANGER HAD BEEN REPLACED JUST PRIOR TO THIS ETOPS FLT. AS WE PROGRESSED WBOUND TOWARDS ZZZ; OIL QUANTITY EVENTUALLY DROPPED TO ZERO AND OIL PRESSURE STARTED TO DROP AND FLUCTUATE. IT BECAME OBVIOUS THAT ZZZ WAS NO LONGER A VIABLE OPTION SINCE OIL PRESSURE WOULD SOON BE BELOW LIMITS. THE SIMPLE DECISION TO MAKE WAS; WHERE TO SHUT THE ENG DOWN WHEN THE ASSOCIATED IRREGULAR PROC DIRECTED IT. THE ANSWER WAS SIMPLE; AFTER LNDG; INSTEAD OF IN FLT. WE DECIDED TO DIVERT INTO ZZZZ. THE ENG CONTINUED TO OPERATE NORMALLY WITH ALL INDICATIONS EXCEPT OIL QUANTITY REMAINING WITHIN LIMITS. THE LOW OIL PRESSURE EICAS WARNING CAME ON AT TOUCHDOWN. THE ENG WAS SHUTDOWN DURING TAXI-IN. FOLLOWED FLT MANUAL GUIDANCE. DISPATCH AND MAINT CTL WERE NOTIFIED AND WERE INVOLVED DURING THE ENTIRE DIVERSION. A CABIN ADVISORY WAS ISSUED.