It was reported on Avweb this morning that Reuters reports that JAL says (talk about third hand info!) that the reason for the BOS fuel spill was an uncommanded activation of a fuel transfer valve which allowed fuel pumped from a "belly" tank (I thought Boeing called them "center" tanks) to overfill a wing tank. Upon arrival back in Tokyo, the same aircraft spilled fuel on the ramp after a valve used to defuel the aircraft opened. JAL has grounded that particular airplane until the cause of these fuel system malfunctions is identified and corrected.
A couple of observations and opinions:
Okay, the xfer valve thing at BOS I can understand. For some unknown reason a xfer valve opened and a wing tank was overfilled causing fuel to exit via the vent. I've seen this happen a couple of times when a crewmember tried to pack the wings and didn't stop in time. In this case JAL is quoted as stating that the valve operated "uncommanded" and are looking for the cause. Makes sense.
But the fuel spill after arrival in Tokyo is less clear. A "defueling" valve is traditionally used to allow defueling of the aircraft through the single point refueling receptacle. I'd be interested to know how a "defueling valve being open can cause a fuel spill. An open "jettison" valve is an entirely different matter though! I'll be interested to see whether something was lost in the translation in the reporting of this incident or perhaps the function of a defueling valve has been redefined.