TW, you're supposed to be seeing the plane.
Many people believe that the fifty+ eyewitnesses to the crash were mistaken about what they saw, and that no plane crashed into the Pentagon at all.
It's part of some sketchy and poorly-reasoned conspiracy theory about 9/11, wherein the U.S. government stole five passenger jets full of people, hid them somewhere, killed their passengers, hid the bodies, and then used missiles and/or death rays and/or remote-controlled planes and/or mind control to create the illusion that the planes had actually been crashed into buildings (and the ground in the case of "Flight 93").
Some believe that the release of the Pentagon security footage would debunk this conspiracy theory, but I have some doubts. For one thing, the footage isn't very conclusive except perhaps through expert analysis. For another, most conspiracy theorists are adept at ignoring evidence that contradicts their theory. This footage will undoubtedly be rejected as government fakery, and the expert analysts dismissed as government stooges.
To see the Conspiracy Theorists debate tactics in action, check out http://apollohoax.proboards21.com/index.cgi?board=theories