25 years after 9/11: How four hijacked planes changed US security

On September 11, 2001, four hijacked planes were involved in a series of attacks in the US. American Airlines Flight 11 hit the North Tower of the World Trade Center at 8:46am.

The attacks continued with another plane hitting the South Tower, one crashing into the Pentagon, and a fourth plane crashing into a field in Pennsylvania after passengers fought to regain control.