Date: 201510
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: B747 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Fuel System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Human factors: Troubleshooting; Confusion
Second reporter function: Relief Pilot; First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We departed enroute to VHHH. When reaching cruise we got an EICAS message for a fuel imbalance between the #1 main fuel tank and the #4 main fuel tank. They were imbalanced by approximately 5000 lbs. The configuration didn't make sense because all the fuel was being drawn from the stab tanks and then the center tanks. We checked the fuel load sheet and verified that the fuel was in fact boarded properly; it was. We balanced the fuel by burning gas tank to engine on the #1 main tank and after achieving a balance; reconfigured the fuel system to normal operations. While taking our fuel scores at each waypoint; we realized that we were low on fuel at every check point. It started out as 1500 lbs low but was progressively getting worse. We scored 5000 lbs low after about 2 hours of flying and we were forecasted to be 6600 lbs low at the next waypoint. All other items on the flight plan were normal. We ran all applicable check list; the first being the imbalance checklist then the fuel leak checklist. We had signs of a leak but the totalized fuel was consistently greater than the calculated fuel. This caused some confusion as to why this was happening if we had a leak. We woke up the 2 relief pilots and got them involved with the situation. After we all determined that we had some sort of leak and that we no longer had enough fuel to reach VHHH; we elected to return. We needed to jettison fuel before arriving in order to be at max landing weight on arrival. It was determined that we could begin this process 50 minutes prior to landing so as to be completed before we descended to land. During the Jettison process the fuel became imbalanced again and we stopped the jettison. This left us with about 8000 pounds of excess gas so we flew lower and configured the airplane to burn the fuel more rapidly. We landed at 631.8 lbs GLW (Gross Landing Weight) without incident and the emergency crews met us off the runway to inspect the airplane. Nothing was noted by them so we returned to the gate. On arrival into the gate; the calculated fuel was 2000 lbs greater than the totalizer fuel. We briefed the mechanics and then left the airplane.


Second narrative: I was scheduled for short call reserve beginning at XA00. I was called at XB39 to fly to VHHH. I promptly left for the airport and arrived at XE20 due to heavy traffic. The flight was delayed due to difficulty getting the flight crewed; but pushed off the gate at approximately an hour later. We took off for Hong Kong but ended up with a fuel system problem. We decided to return. We briefed the mechanics on the problem then left the Airplane. I called the hotel desk to get us rooms due to the duty day and time of day but nobody answered. I then called the Duty Manager and secured 4 [hotel] rooms. While waiting for the hotel van at approximately XO00 I was notified that the flight was delayed and we were to depart at XE20 to VHHH. I arrived at the hotel at around XO50 and was in bed by XP20. I woke up at about XT15 and laid in bed for about an hour trying to get more sleep but to no avail. Realizing that I was going to be on duty for another 17+hrs and 14+ flight time and having inadequate sleep; I elected to call in fatigued at XV49. In summary; I was awake for approximately 23hrs 45min before I was able to obtain any rest. Due to my irregular circadian rhythm; I was unable to get proper rest. Facing another WOCL (Window of Circadian Low); I took the safe action of calling in fatigued.


Synopsis: Two B747 First Officers describe a fuel anomaly that may be the result of a fuel leak. Several hours into the flight the crew elects to return to the departure airport due to insufficient fuel to reach their destination. The flight is rescheduled to depart 14 hours after returning but one of the First Officers is unable to get meaningful sleep in the allotted time frame and calls in fatigued.