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"...the real problem is rarely if ever addressed: how do we effect a solution that will guarantee an airplane will never again be flown into a building?"
Robert A. Heinlein wrote an article called "The Billion-Dollar Eye" discussing ongoing plans to create an automated system to control aircraft across the country. This system was being considered in Congress. Unfortunately it was considered too expensive to implement.
Heinlein wrote the article in 1948. He was never able to get it published.