16- PHL-STL, four stops, 1970
the fact that you haven't explicitly mentioned availability of F, or that the equipment was a jet, leads me to believe we may have an American Airlines Lockheed Electra; I don't recall the big turboprop serving PHL that late in its AA career, but what the heck ... let's say Washington National (DCA), Charleston WV (CRW), Cincinnati (CVG), and Louisville (SDF)