14 CFR § 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.
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