"Small cargo aircraft" was operated by Ameriflight, a contractor for UPS. It apparently was repositioning to be fueled. Reports differ on closeness - FAA says 100 feet - NTSB says 10-20 feet. Either way, it was close. If it was an MD or larger,or a heavily loaded F-100, it probably would not have reached Vmu. (Ok, flight test guys - is this a reasonable use of the term Vmu?)