Although the runway at Northolt is 5,500ft approx, it has a major road at one end and housing at the other, which to the best of my knowledge Renton does not. Imagine the insurance implications for PanAm back then if something went wrong, even in a minor way and that's not counting
PR and customers. I'd imagine that it was kept on the back burner press wise at the time. If such a thing happened today what with smart phones and twitter etc, it would severely dent a corporate image
SHJ