Originally Posted by
longer ron
By 1917/18 RFC/RAF pilots were regularly doing high altitude patrols at 17,000ft up to sometimes 21,000ft (depending on a/c type) - not a healthy occupation without oxy and pressurisation.
I have been up to 11,500ft quite a few times in a glider without oxy with no ill effects but I usually did not stay above 10,000ft very long
I guess you become acclimatised to the altitude a bit like Mountaineers. 21'000 feet is pretty high though.