Date: 201910
Local time of day: 0601-1200
Location: ZZZZ.Airport, FO
Flight conditions: IMC
Weather elements / visibility: Turbulence; Windshear; Rain
Light: Night
Aircraft: B777-300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ZZZZ
ATC / advisory: Center ZZZZ
Aircraft component: Fuel Quantity-Pressure Indication
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer; Relief Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew FLC Overrode Automation
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During our arrival to ZZZZ; we were held and vectored off course for weather and a priority aircraft. After vector delays; we were cleared for approach. On approach and at about 2;500 feet; ATC issued a microburst alert of winds at +/- 40 KTS and shear of 800. After; the aircraft preceding us went missed approach and at about 1;900 feet; we went missed as we encountered the microburst and uncontrollable airspeed fluctuation. During vectors after the missed approach it was evident we would not be able to make another approach into ZZZZ; so we diverted to ZZZZ1.After several attempts to get a course or heading to our desired destination and evaluating our fuel; [we identified as an emergency] as our fuel on landing was indicating 4.1 on touchdown. After climbing and evaluating the situation; we determined that the fuel on board and the calculated fuel in the FMC were not in agreement so taking the safest course of action we changed our alternate to ZZZZ2 as it was closer and gave the FMC fuel on landing of 8.1. We landed and had 18.0 in the totalizer and 8.2 in the FMC.


Second narrative: Flight to ZZZZ with ZZZZ1 as an alternate. We were on fuel schedule when we received a low altitude hold inbound ZZZZ. Left hold and proceeded towards airport on the STAR when we were turned away due to an inbound emergency aircraft. Vectored around and was finally cleared for a second time for the approach to 34L. We were fully configured at 2;500 feet and at our target speed with the autopilot on. Towers had cleared us to land and moments later announced a microburst alert. At 1;900 feet; our speed went to plus 40 knots and First Officer (Pilot Flying) promptly and appropriately announced going around. We were still IMC; and in light to occasional moderate turbulence. Cleared to fly the published missed; which we did. Climbed to 4;000 feet and received a heading from departure control to fly approximately east. Quickly discussed with crew our fuel situation and all agreed we did not have enough fuel to attempt another approach; miss; and proceed to alternate; so we asked an extremely busy departure control for a clearance to ZZZZ1 and a climb. Fuel was becoming an issue but we were still showing enough on the totalizer. After installing ZZZZ1 in the FMC the fuel remaining value was showing around 3;000 lbs. We we're extremely busy with Communication; flying aircraft; and trying to rectify why we were going to have so little fuel on arrival in ZZZZ1. During this time; we were having no success in getting a clearance to ZZZZ1 or even a turn towards the alternate. After 3 or 4 attempts to get some kind of a clearance to alternate; we decided due to our fuel situation and the fact we couldn't rectify why the fuel remaining was so low on arrival we decided to [identify as] a fuel emergency. By doing so; we did get a clearance to climb and a turn towards ZZZZ1. Proceeding towards ZZZZ1 and still unable to resolve our fuel dilemma we changed our alternate destination to ZZZZ2 as it was considerably closer and had good weather. Received approach and landing clearance and landed without incident. Arrival totalizer fuel showed 18.1 but FMC was showing 7.6. We were never able to identify the difference in the two; which was the determining factor in wanting to get aircraft on ground and to operate the aircraft as safely as possible.


Synopsis: B777 flight crew reported that fuel quantity on the totalizer and the FMC were not in agreement.