Was just thinking...if there were normal engine contrails as well as the wing tip trail, that would suggest some condensation occuring? But as there were no normal engine contrails at all and the aircraft was reasonably low, would that suggest there wouldn't be any other condensation and that the fuel theory might be the most likely in this case?
Am enjoying all the contributions and thoughts on this one. Oh, QF 093 flew over this morn, again reasonably lower than a Virgin Blue flight that was just ahead of it..normal contrails today and nothing from wing tip. Cheers Tim