The NORAD was told to "stand down"

When an airplane is hijacked, the North American Aerospace Defence Command (NORAD) is prepared to send fighter jets, that can shoot down the aircraft.

On 9/11 the general of the NORAD told that they knew about the hijacking of the planes. Some skeptics believe the NORAD was told to stand down, because of their lack of presence during attacks.

Aircrafts didn't made the towers collapse

The Twin Towers collapse looked similar to a controlled demolition. Some believe the towers were in fact blown out by explosives placen in the tower and not because of the planes.

Some scientists have proved that it wouldn't be possible for the planes fuel to cause an explosion like that, and that aircrafts are made of a really light aluminum material so they can fly with so much weight on them, so they couldn't cause such a crash.

Flight 93

The fourth hijacked plane, flight 93, crashed in Shanksvill, Penn. It's believed that the passengers fought back to the attacks and crashed the plane in a field.

Others think thai flight landed safely, meanwhile another plane was shot down to look like flight 93, and the passengers where relocated and then murdered.

Faked cellphone calls

In-flight calls were made from the passengers phones to friends and family, but according to scientists and skeptics have a strong believe that phone calls could not receive reception from the altitud planes normally fly on. Which backs up the theorie that the passengers landed safely and were transferred somewhere else.

Others question the calls because, according to the people that recived the calls, the person calling would start by saying their full name and last name. Which isn't something you would normally do when you call your mom.