Twenty-three years ago, F-16 fighter pilot Marc Sasseville was sent on a mission that he thought could be his last.

Two hijacked planes had flown into the World Trade Center’s twin towers in New York City, and a third had struck the Pentagon. Sasseville received orders on Sept. 11, 2001 to prevent another hijacked airliner headed for Washington from reaching its target. That plane was United Airlines Flight 93, which had been hijacked by four al-Qaida terrorists and ultimately crashed in Shanksville, Pennsylvania.

In an ABC News exclusive interview, Chief…