Originally Posted by cessna157

Can someone explain something to me. I've been trying to work the math on it, but I just cannot get the numbers to work out here.
I saw an article in the paper a few days ago about the near mid-air at ORD earlier in the week. The paper quoted someone by saying "The 2 aircraft came within 400 feet of each other, and it was just chance that they didn't hit at that range".
So, if 2 airplanes are 400 feet apart, they are expected to contact each other?