TCAS design engineering meeting sometime in the 80's:
"Right, let's make the threshold 159kt. No-one will ever be trying to land faster than that without wheels. All in favour say Aye"
"Aye"
"Aye"
"OK that's it then."
Somewhere on a rocking chair in the sunroom of a house, with a throw rug on his lap is a retired engineer shaking his head today.