The National Transportation Safety Board continues to investigate two near-midair collisions at Chicago O'Hare International Airport. The investigation focuses not just on air traffic controller error, but the control tower configuration and dual intersecting runways.
Links:
[1] http://www.library.northwestern.edu/libraries-collections/evanston-campus/transportation-library
[2] http://www.insurancejournal.com/news/midwest/2012/09/27/264635.htm
[3] http://www.library.northwestern.edu/related-pages/ohare-airport