Pace, everyone would pass out at 25,000 feet.
Even if Superman was a smoker - so would he.
Runaway Gun
Not so ! climbers have climbed mountains higher than that without oxygen and with exertion which pilots dont have although I add they are conditioned to it first.
I have taken my oxygen mask off for short periods at 20K and once ran out of oxygen in 70 kt headwinds over the alps at X
for a short time.
While I agree plus 30K you have had it 25 K is marginal and depends on your fitness, Whether you compress breathe, your lung capacity, how tired you are, whether your a smoker, your weight, general health etc as well as how long you are there.
But in tests not all pass out at 25 K
Have a read of this extract from a test pilot of old it makes interesting reading
1943 | 1754 | Flight Archive
Pace