On Sat, 01 Jan 2005 19:34:03 -0600, Don Hammer wrote in
::

... it used to be a fairly frequent
occurrence for airliners to hit small aircraft. Of course the press
always got it the other way around. That's why we have to have
transponders is certain airspace in small aircraft.

Here's the MAC that lead to mandatory TCAS:
http://www.ntsb.gov/NTSB/brief.asp?e...13X34444&key=2