Widebody Transport
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Troubleshooting
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft
Assigned aircraft with 5 MELs including a Main Tank 2 Transfer pump inoperative. Procedure was to operate the Fuel System Controller (FSC) in manual. Discovered in the Aircraft Maintenance Log (AML) that aircraft had departed with this MEL and upon arrival; the inbound crew wrote up uncommanded fuel transfer enroute. They apparently found it necessary to rebalance fuel throughout the flight. We questioned maintenance about the two writeups and they were convinced the fuel transfers were related to the inoperative transfer pump.Soon after departure; it was evident that the uncommanded transfer was still occurring. We monitored it for a short while after established in cruise -- and specifically avoided any attempt at rebalancing so as not to further mask the real problem or induce yet another problem. We concluded that something very significant was happening and coordinated with Company for a diversion. We recorded the fuel used and fuel quantity data at various points while in flight and at block in it clearly showed that fuel was either; A) being transferred tank to tank uncommanded; or B) the quantity indications were unreliable. This data is being retained by the Captain and can be presented if desired.
[Report narrative contained no additional information.]
Widebody aircraft fuel system developed transfer and balance issues uncommanded. The aircrew diverted enroute as a precaution.