The oxygen requirements only come into play when you fly depressurized. The reason that passengers aren't on oxygen when you are flying pressurized at 30,000 feet (probably 5-7,000 ft pressure altitude inside the plane) is that the air they are pressurizing (thin, high altitude air) is still the same ratio of nitrogen/oxygen/CO2 even though there are smaller amounts of each.

The FAAs requirement of people being on supplemental oxygen only matters in non-pressurized flight, like small Cessnas and pressurized aircraft experience a depressurization emergency.

[–] Rivalarrival@lemmy.today 2 points 1 week ago* (last edited 1 week ago)

The oxygen requirements only come into play when you fly depressurized.

That is true for the 12,500, 14,000, and 15,000 feet cabin pressure numbers I gave, yes.

However, the oxygen requirement associated with the 35,000 foot number I gave applies to both pressurized and unpressurized flight. If your aircraft is at or above 35,000 feet pressure altitude, at least one of the pilots must be on oxygen, or must have a quick-donning mask available at all times.