Seventeen years after the devastating 9/11 attacks, President Donald Trump heads to Pennsylvania on Tuesday to pay tribute, as his predecessors have done, to the men and women who died aboard hijacked Flight 93.

On September 11, 2001, the plane -- one of four commandeered by Al-Qaeda militants -- crashed into a field in the small town of Shanksville, about 130 miles (200 kilometers) northwest of Washington. Those aboard United Flight 93, told over the phone by their loved ones that two other passengers jets had smashed into New York's World Trade Center, tried to regain control of their aircraft.