If memory serves, didn't Purdue also note that NIST underestimated the damage (after their study)?
Everybody noted that -- Purdue, Northwestern, MIT, Arup, everybody. NIST's is the most conservative of all the professional WTC collapse studies. I noted this in my whitepaper all those years ago...
It also makes sense if you comprehend the purpose of the NIST investigation. Their project was not, as Truthers still cannot fathom, an attempt to "explain the unexplainable" or to construct a narrative that counters wild speculation about explosives. (The notion that "NIST needs the Truth Movement," or AE911T in specific, is risible at best.) NIST's purpose, as spelled out in the National Construction Safety Team Act of 2002, was to study the disaster for the purpose of
making recommendations about construction standards.
When you perform this type of a study, you naturally adopt a conservative tone. It does no good to make recommendations about effects that "might possibly" have happened, or to base conclusions on unsupported assumptions. This distinguishes the NIST study from others, looking to evaluate possible mechanisms (e.g., U Maryland) or come up with a "best guess" reconstruction (as in Purdue). So as a result, NIST is demonstrably conservative in several dimensions. Its estimate of energy absorbed by the aircraft at impact is ambitious, and its estimate of fuel loading on individual workstations is surprisingly low (as noted by Dr. Wierzbicki and myself). Its estimate of combustibles in the WTC Towers is a lower estimate and thought to be well below typical norms (as Dr. Quintiere pointed out). Its inclusion of creep and system instability are understated (per Arup) and its estimate of fire spread in WTC 7 is limited to boundaries supported by observations at the perimeter.
As a result, there is room for criticism of its conclusions, but their approach nonetheless makes sense. "Criticism" by the way does not mean "make up crap about mythical explosives" or what have you -- I'm talking about professional criticism, the kind levied by Dr. Quintiere or CTBUH.
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With respect to the impact angle of UA 175, I haven't followed the calculations leading to
femr2's claim that NIST is off by seven degrees, however this strikes me as "plausible." This corresponds to about 3 sigma of discrepancy between measurements, a significant difference but not an impossible one.
What does surprise me, though, is that if NIST's estimate was off by seven degrees, I would expect to find poorer agreement between their damage simulation and the actual observed damage at the perimeter of WTC 2. In particular, the breakthrough opposite the impact. Ultimately, provided the exterior damage is a good fit, the interior damage estimate is probably decent as well.
I would suggest that there is an excluded middle possibility here -- the aircraft may have been skidding. It is possible that the orientation of the aircraft is better described by
femr2's estimate, but that the actual momentum vector of the aircraft remains a good fit to NIST's.
In any case, this is not a significant enough difference to throw out NIST's result on WTC 2. Purdue varied a large number of parameters in its studies and found collapse resulted pretty much every time. NIST is not perfect, and indeed I've disagreed with it on several fine points consistently, but it is a pretty good study.
