The TV news weather is a very familiar example of chroma key, as the actor is standing in front of a green screen, but to us at home it looks like the whole wall has a satellite map on it.
Yes, and take a good look at the edges of the person, you'll spot the characteristic traces which reveal the background has been inserted.
The aircraft could have been CGI, but there is no reason that it couldn't be a real video. If I were doing it, I would have shot a real 767 flying north simultaneously from a great variety of angles, done so at around 9 a.m. on a clear day, and then taken all the backgrounds out. This would have been done ahead of time obviously. We'd be left with videos of a real 767 flying against a transparency.
My first thought is to say you apparently have little idea just how complicated high-quality visual effects work really is. That reaction aside, I've said it before, but I guess I'll have to say it again:
The three things which always betray a shot is a special visual effects shot:
1) Motion.
2) Lighting.
3) Detail.
If you've got any kind of decent eye, you'll spot one or more of these things which reveal an FX shot to be exactly that. I could spot nearly all the shots which were miniature shots in
The Lord of the Rings films simply by the way it looked (a miniature just doesn't quite look the same as an actual full-size object in terms of lighting and detail). It's subtle I grant you, but when you know what to look for, you can spot it practically every time.
What you're proposing would not work, as the tell-tale signs I mentioned would reveal themselves quite clearly. You'd have had to photograph that 767 from ALL of the necessary angles (which is in the area of 40). Then you've got the explosion itself, that has to be added along with the light that explosion casts. And that's often where VFX shots fail in terms of detail: they'll have supposedly bright or glowing objects in the frame, and yet the object does not cast light onto the surroundings or actors. I expect most folks don't notice this sort of thing, as it is subtle, but I sure notice it.
Then the act of compositing that pre-existing aircraft footage
live would be crude at best. It would be readily apparent. Which is exactly why VFX shots often take months to complete, as ALL the elements of the shot are composited together so that there's only one piece of film to run. If you're trying to pass something off as real, you need a lot of time and resources to do it convincingly, especially to fool VFX eagle-eyes like me; it is most definitely NOT something you can knock off in an afternoon.
EVERY single video of the aircraft impacts into the WTC towers show NONE of the typical signs of a VFX shot. Not a single one. Add to that the thousands who SAW the aircraft with their own eyes, and your theory is reduced not just to the level of implausibility but to absurdity.