I agree with the "one pilot at the controls" rule, but one pilot to wear the mask at all times above a certain altitude (and different alt's for different FAR parts???) is really outdated. I know that many disagree with this based on time of usefull consciousness numbers. However, check an aviation safety database and search for pressurization accidents and see what you find. There are very few and most occur before the A/C reaches high altitudes. Also, with the advent of Emergency Descent Modes (autopilot/autothrottle automatic descents) on more and more aircraft, it's time for a rule change. And yes, I remember the unfortunate Payne Stewart accident. I just think there are better ways to improve safety.