Hola obgraham -
xxx
Indeed - cabin masks are working (let me use the word "somewhat") for typical 10-15,000 feet. I did not say worthless at these cabin altitudes... but I dont count on them to do their job at 20,000 feet.
xxx
One thing we all have to do on Pprune, you, myself and everyone else, is read what the words are and what they mean. According to FAA (and probably JAR 25 since similar), cabin masks sustain life up to 14,000 feet cabin altitude. Beyong that... it is a guess.
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You know, it is funny... What I pass along here in Pprune, as info to people, from aviation enthusiasts to pilots, are official information I teach (or my instructor team teach) with my airline. If I am wrong, realize that my own airline crews are all wrong, and maybe could be subject to a lawsuit for training malpractice...
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Our official policy, in Argentina is...
Maintain cabin altitude below 8,000 feet when possible.
If circumstances dictate, acceptable (unlimited time) at/below 10,000 feet.
In case of system failure, cabin to be maintained at/below 14,000 feet.
If ground elevation does not permit, in function of min. enroute altitude.
xxx
Cockpit crew using O2 if cabin altitude above 14,000 feet.
Recommended use of O2 when cabin altitude exceeds 10,000 feet.
Remember... we operate to La Paz in Bolivia.
We have a circuit breaker to pull to prevent cabin altitude warning.
And to prevent cabin O2 masks to drop at 14,000 feet.
(Boeing high altitude operations STC)
xxx
Hope we get a doctor from the aeromedical branch here... Cheers -
Happy contrails