Originally Posted by Nick227
The NIST Report estimates the sensitivity of its results at numerous points in the narrative, and in most areas provides bounding cases as well.
Variation exists in the force of impact and relative strength of aircraft vs. building materials (NCSTAR1-2), the amount and distribution of flammable materials (NCSTAR1-5), the amount of fireproofing loss and coincident transfer of heat to the structure (NCSTAR1-5 especially 1-5G), and the structural response of the building (1-6). NIST also compares its results to no less than five independent studies (1-2 and 1-6) and attempts to reconcile the results. As I stated on the previous page, there are still some unanswered questions, but the overall conclusion of why and how the structures failed is explained to an extremely high degree of certainty.