India, Sept. 9 -- On September 11, 2001, al-Qaeda hijacked four commercial passenger aircraft across the US, turning them into weapons in a meticulously planned assault.

Two of the hijacked planes struck the Twin Towers in New York and a third crashed into the Pentagon.

When the fourth flight - San Francisco-bound United Airlines Flight 93 - lifted off from Newark, New Jersey, at 8.42 am, the three hijacked planes were already in the air, closing in on their targets. The three crashes had set off harried security checks across the country.

According to the 9/11 Commission report, Flight 93's departure was delayed by around 25 to 40 minutes due to congestion at Newark. This delay would end up playing a crucial role in how the day's even...