As I lack a background in avionics, I consider myself fortunate to have found such a valuable resource as this forum. The knowledgeable people here should be aware, however, that a bizarre subset of the 9/11 conspiracy cult believes that no planes were involved in the events of that terrible day. To promote this mad thesis, these "no-planers" try to twist the words of pilots and aeronautical engineers to "prove" that UA 175 could not have been flying at roughly 550 mph when it crashed into the South Tower. When someone appears to inquire innocently about the speed limit of a Boeing 767 at sea level, please understand that a "truther" is playing a perverse game.