Regarding woodpecker's post. Would the ice in the centre tank really be able to melt enough to cause enough liquid water to make a problem? Or wouldn't it be more likely that it could only melt enough to create a slush? If slush was pumped from the centre tank to the wing tanks, then could this slush have collected on the intake filters or elsewhere in the fuel delivery system and caused a major restriction in fuel flow? It would only take a relatively small amount of slush to cause a problem which would not be detected compared to the major amount of water required to cause a problem which should have been detected.