No, if you knew about 9/11 beforehand, you would just quietly set up a few surface-to-air missile batteries and pretend that it's a "military show and tell" day or something for the kids.
Then when the planes are hijacked, and are on course to fly into the buildings, you blow them up and say, "Holy shit! It's a good thing these things were here!"
Or you just make sure you put extra security at the airports on that day.
