Looks like CGI to me. 
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Clip is from CNN archives. Plus obviously a real plane cannot just diassapear into a steel frame building or come out the other side. 
I was there and from my rooftop it looked CGI too. And I work in the film industry
I had an excellent view from my kitchen window of the towers from the time of there construction. This staged event changed the world for sure and not for the better.