In the 1960s the future of aviation seemed bright. In 1958 Boeing had built its first jetliner, the 707, which cruised at speeds of up to 600 mph. The Concorde came along in 1969, flying at Mach 2—more than 1,500 mph. An age of affordable supersonic flight seemed inevitable, promising U.S. coast-to-coast travel in just 90 minutes.

Today, neither the Concorde nor any other supersonic passenger jet operates. And the 707, still in limited use, remains one of the fastest commercial jets operating in the world. What happened?

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