D.B. Cooper, the changing nature of hijackings and the foundation for today's airport security

The hijacking of U.S. aircraft – like the three hijacked in 1970 by the Popular Front for the Liberation of Palestine – made it impossible for American policymakers to ignore the threat. Bettmann/Getty Images

Though many Americans may associate airport security with 9/11, it was a wave of hijackings in the late 1960s and early 1970s that laid the foundation for today’s airport security protocols.

During that period, a hijacking occurred, on average, once every five days globally. The U.S. dealt with its own spate of mile-high crimes, convincing reluctant government officials and airport executives to adopt the first important airport security protocols.