FAA Federal Aviation Regulations (FARS, 14 CFR)

(a) If certification with supplemental oxygen equipment is requested, the equipment must meet the requirements of this section and §§25.1443 through 25.1453.

(b) The oxygen system must be free from hazards in itself, in its method of operation, and in its effect upon other components.

(c) There must be a means to allow the crew to readily determine, during flight, the quantity of oxygen available in each source of supply.

(d) The oxygen flow rate and the oxygen equipment for airplanes for which certification for operation above 40,000 feet is requested must be approved.