Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 29000; Flight Crew Type 500
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
We departed and upon level off at FL300 we noticed an EICAS 'FUEL IMBALANCE 1 and 4'. The entire crew looked at the fuel synoptic in disbelief because fuel is not burned out of 1 and 4 by system logic until tanks 1;2;3;4 are approximately even (about 30k pounds). We ran the fuel imbalance check list and tried to determine if we had a leak but totalizer and calculated fuel were about the same and no other factors indicated to us that we had a leak. We balanced the fuel between tanks 1 and 4 by closing #1 crossfeed. When the levels were within 800 pounds the balance was close enough and we opened crossfeed 1 again. Fuel balance remain good until late in the flight. FO became alarmed when we got to our next fix and we were down 1500#. I had a wait and see attitude and recommended we press on and maybe we would get the fuel score in line with the OFP. By the next fix we were down 2500# on the fuel score and the FO advocated and I agreed to contact [Maintenance]. [Maintenance] downloaded our data and told us there were no fuel error codes and that he recommends we continue our flight but keep a close watch on the fuel. A few fixes later we were 5500 to 6000# down on the fuel score so I told the FO that I felt we should divert and if he agreed; also wake the [relief pilots] up and prepare for the divert. We did NOT initially declare an emergency but when we started dumping fuel to get down under the max landing weight we got out of balance again between tanks 1 and 4 by about 5000#. I told the crew to terminate the dump and I [advised ATC] - mainly because I had no confidence in the fuel indicators and that we would most likely land overweight. We requested a lower altitude to burn fuel to lighten the weight and I pulled speed brakes to assist in the burn. Flight attendants were briefed and we did ask ATC to 'roll the equipment.' We landed 1.9 over max landing and the landing was uneventful.
B747 Captain reported diverting to an alternate after noting fuel quantity indication system anomalies.