Sec. 25.1445 - Equipment standards for the oxygen 
      distributing system. 
      (a) When oxygen is supplied to both crew 
      and passengers, the distribution system must be designed for either --
      
      (1) A source of supply for the flight 
      crew on duty and a separate source for the passengers and other 
      crewmembers; or 
      (2) A common source of supply with means 
      to separately reserve the minimum supply required by the flight crew on 
      duty. 
      (b) Portable walk-around oxygen units of 
      the continuous flow, diluter-demand, and straight demand kinds may be used 
      to meet the crew or passenger breathing requirements.