Answer and explanation:
The 9/11 attack is possibly one of the most horrible events in American History. Terrorists from armed-group Al Qaeda infiltrated as passengers of American Airlines, took control of the plane threatening people with fire guns, and eventually crashed the plane into the World Trade Center in Manhattan, New York City (2001).
From the economic point of view, it would reasonable if airlines increase investment in technology and resources that allow them to improve their screening process to avoid such moments to be repeated in the future. Eventually, the costs of not conducting a proper passenger screening could be higher, not only economically speaking.