The CF6 has had it's share of premature departures too. Atlas has left one in a back yard in Guayaquil (Sp)! I believe but can't confirm, that LH landed and had one half hanging off in the late '70's. Other factors of Freighters VS Pax 74's is that because of the higher weights, the freighters usually cruise at lower altitudes, encountering more turbulent air. Some freighters are certified to land at 302K vs 285K. It all adds up to, more weight, more all around stress across the whole flight envelope. It seems to me too that the Freighter is usually more heavily utilised ( no pun intended!)