If you stand a quarter of a mile or so from the threshold at PDX 28R, (or at
the cemetery at McCarran in Las Vegas, the incoming), you hear a windy,
howling sound that is so well defined it seems to take shape in the sky
after the larger jets have passed for touchdown.

Has anybody heard it? What is that? Our theory has always been that its
the wingtip vortices collapsing.

-c