9-11/official

About
What is generally considered to be the official account of the events of 9-11 is largely derived from a number of reports issued by various government-authorized bodies. These are supplemented and refined by scientific and academic papers either analyzing those reports or reporting on separate analysis of available evidence.

The official story is apparently seen by most people – without regard to political affiliation – as the rational view, and is typically contrasted with the many anomalies which have been unofficially identified and the many "conspiracy" theories unofficially advanced to explain those anomalies, which are seen as obsessive or "wacko".

Pages

 * /reports: the major reports which comprise the bulk of the official story
 * /papers: scientific and academic papers refining some of the details not adequately addressed in the reports, or providing evidence used in them

Narrative
This is an attempt to summarize the official story, and may include some details within are not generally agreed upon; we will be refining it over time as we reconcile it with mainstream media reporting and official sources.

On the morning of September 11, 2001, terrorists working for Al Qaeda and on the orders of Osama bin Laden boarded four airliners as passengers. Soon after take-off and using only boxcutters as weapons, they overcame the crew and pilots, took over the controls, and succeeded in directing three of the planes into their intended targets -- WTC1, WTC2, and the Pentagon. On the one remaining aircraft, passengers heard via cellphone about one or more of the other incidents, and decided to fight back, resulting in the plane crashing into an uninhabited field in Pennsylvania, thereby probably saving many lives.

The military jets which are normally deployed within minutes to intercept troubled aircraft were unable to intercept the planes before they reached their targets, in part because the commercial jets' transponders had been turned off, making them difficult to track.

Overcome by the intense heat from the burning jet-fuel and having had their insulation partly stripped away by the impact, critical structural elements in WTC1 and WTC2 became sufficiently soft that the block of stories above the impact collapsed one or more floors in the impact area; the momentum built up from this initial collapse was sufficient to collapse the less-damaged floor below that and ultimately the rest of the building (one floor at a time in a downward progression). The mostly-intact upper floors presumably collapsed on themselves when the accumulating pile of rubble ran into non-compactable soil or bedrock below street level.

The damaged Pentagon also burned out of control for some time, resulting in collapse of its upper floors over the impact area.

Fires and debris from the collapsing WTC1 and WTC2 heavily damaged or destroyed several other buildings, starting fires throughout the World Trade Center complex which burned out of control for the rest of the day and eventually caused WTC7 to collapse that evening.

Details
Some specific allegations within the official story:
 * WTC 1 & 2 :
 * The floors did not "pancake" into each other; that theory was advanced initially, but later retracted.
 * The final explosions were not jet fuel exploding, but the result of mechanical collapse.
 * The mechanical collapses were due to the fires weakening (not melting) the structural steel in the floors, causing the floors to sag and pull in the sides of the building.
 * WTC 7 :
 * The collapse was due to fires spreading to an area where they were able to weaken 9 floors of a critical support column.
 * The fires were only able to spread that far because the sprinkler system was not working.
 * Mechanical damage from falling debris was not implicated in the collapse. (This is not stated explicitly; it is simply not mentioned as a cause.)

Links
Links listed here are not official, but they are generally undisputed and are often used in defense of the official story.
 * Inside the South Tower: Eyewitness Accounts