Notice the tower poised like a figleaf over the hard-to-animate impact spot.
Notice that the first frames show a "plane" with realistic highlights and then it turns to a solid color.
Notice there is on shift
in size as would be seen from a camera in any single position.
Instead, the footage is a "gods eye view" as tho the camera were accompanying
the "plane" from an equal distance throughout. (Actually a still projected
on a moving backdrop)
Notice that the explosion on the opposite side of the building is fully engaged before the explosion at the "impact point" is visable.
This shows an angle planned well in advance so that live footage of the explosion could be combined with previously created animation.
The live portion shifts a little too far to the right, and shows a couple frames of the actual perp.