How close to supersonic was UA175 going if it was clocked at 586 m.p.h.? Presumably if it had also been put into a dive at that time it could even have exceeded that speed. In the absence of any further flight control inputs would it have broken up in mid-flight if it had gotten anywhere near to Mach 1?
Re Localiser's post: one would have expected Boeing to have some kind of speed limiter to prevent the plane from getting anywhere near to design limits in straight and level commanded flight. If the Airbus has it, then why not Boeing?