North American Aerospace Defense Command (NORAD) found out about the hijacking as Flight 11 suddenly went silent. Photo: Getty Images

Air Traffic Controller heard a mysterious voice, which asked him to stay put and not do anything 'stupid.' Photo: Getty Images

At 8.46 am, flight 11 crashed into the North tower of World Trade Center in New York. Photo: Getty Images.

Minutes later, at 9.03 am, another flight (175) crashed into the South Tower of the World Trade Center. Photo: Getty Images.

At 9.37 am, the hijackers crashed Flight 77 into Pentagon, Washington DC. Photo: Getty Images.

At 10.03 am, Flight 93 crashed in an open field near Shanksville, Pennsylvania. Photo: Getty Images.

It's believed that the hijackers intended to crash flight 93 into either the White House or the Capitol building. Photo: Getty Images.

As passengers began taking control of flight 93, the hijackers intentionally crash landed the plane at Shanksville in Pennsylvania. Photo: Getty Images

The South Tower collapsed at 9.58 am and burnt for 56 minutes before collapsing. Photo: Getty Images

The North Tower collapsed at 10.28 am, more than a couple of hours after it had been crashed into. Photo: Getty Images.

Burning debris from the North Tower fell on the 7 World Trade Center building (7WTC) Photo: Getty Images

The 7WTC collapsed in the evening that day. Photo: Getty Images.

Aircrafts were grounded and those already airborne were asked to land immediately, fearing a further attack. Photo: Getty Images.

All international flights were banned from landing on US soil for three days. Photo: Getty Images.

U.S. President George W. Bush speaks to Vice President Dick Cheney by phone aboard Air Force One September 11, 2001 after departing Offutt Air Force Base in Nebraska. Photo: Getty Images