I found the 545.64 kts at 32000 feet Mode C/ 33600 feet primary radar height. My calculations give a 0.86 mach velocity of 502.61 kts for this 32 Kft altitude.

At P4T there is a thread about Flight Test Limits being verified to 0.92 mach by Boeing engineers (not certain on plane model). My calculations give 537.68 kts (again 32 Kft) at this 0.92 mach "overtest" level that mentions flapping wings and nearly-destructive flight. In the conspicuous absence of FDR's and CVR's, we can only speculate about the goings on inside the Boeing, but if I were hypothetically tasked with "suicidal Jihadist Boeing missile duty," I'd probably want to be certain that the plane ACTUALLY made it to the target rather than risk destroying the Boeing in mid-flight.

I believe that Joseph Keith was referring to the low-altitude increased air density and drag, especially on the jet turbofan engines (only rated to 105% of maximum rated shaft RPM from my research in FAA datasheets). A female Boeing aerospace engineer in one of the videos was laughing via telephone about the feasibility of 500 mph velocity near 800 feet ASL. Incidentally, the last 3 RADES radar returns averaged 501 mph by my estimates, so there is ONE thing that approximately checks with the "official" box-cutter conspiracy story (although it appears to contradict the 2 Boeing engineers).

Another interesting anomaly that I believe contradicts the "eyewitness" and video accounts of the UA175/WTC2 South impact- the RADES data shows an altitude decrease of over 8000 feet in the last minute of flight. Wasn't the video of a relatively "flat" Boeing approach, banking to the port side immediately before impact? I haven't calculated the dive angle yet from dive & lat/lon (GS velocity), but the USAF/FBI RADES data seems to contradict the video "evidence" IMHO- both simply CANNOT be true from my observations.