After "pulling out" individual frames, the object can be seen a bit accurately, although the image quality is still not very interesting.

It seems that the same object flying at great speed was captured on film but in a different shot and from a much greater distance.

To facilitate recognition in the situation - below - I present individual frames from the shot. The red triangle marks the Unidentified Object, and the yellow triangle marks the second plane heading towards the WTC, which will collide with the building a few moments later ...