O2 requirements

F

FOD

Well-Known Member
I have always been under the impression that the oxygen requirements above 12,500 ("more then 30 minutes duration") is cumulative, but havent see it anywhere. Someone wanna clear this up for me?
 
FOD said:
I have always been under the impression that the oxygen requirements above 12,500 ("more then 30 minutes duration") is cumulative, but havent see it anywhere. Someone wanna clear this up for me?
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§ 91.211 Supplemental oxygen.

(a) General. No person may operate a civil aircraft of U.S. registry—
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;
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Couldn't find any either, but it has always been my understanding that it is cumulative as well. If you are above 12,5 for 28 minutes and go below for a minute and then come back you only have 2 minutes left. That may be the extreme example, but that's the impression I was given during training.

Looking at the bolded, if you are on a flight of 2 hours, and go above 125 for 10 minutes and then back down, and then back up....you have 20 minutes, you are still on that flight. Given that, I would say it is cumulative.

Bueller, Bueller??? Anyone????
 
when i was going for my inst. ticket my instructor asked me this question. i said you could dip below 12500 for a little and come back up, and you'd get a brand new set of minutes, she said yep. (but maybe it is cumulative?) is it good practice? nah, you're risking too much there, like FOD said.
 
caliginousface said:
when i was going for my inst. ticket my instructor asked me this question. i said you could dip below 12500 for a little and come back up, and you'd get a brand new set of minutes, she said yep. (but maybe it is cumulative?) is it good practice? nah, you're risking too much there, like FOD said.
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Wow now that is a good hangar question. I'm going to spread that one around a few places.
 
caliginousface said:
when i was going for my inst. ticket my instructor asked me this question. i said you could dip below 12500 for a little and come back up, and you'd get a brand new set of minutes, she said yep. (but maybe it is cumulative?) is it good practice? nah, you're risking too much there, like FOD said.
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When you think about it that way, the reason you get 30 more minutes duration is that theoretically you have returned to the level of the atmosphere where the partial pressure is significant enough to return your oxygen supply and distribution to normal levels. Would I dip below 125 for a minute and go back up? No, but if I came down to 5k for 30 minutes I might consider going back up.
 
moxiepilot said:
When you think about it that way, the reason you get 30 more minutes duration is that theoretically you have returned to the level of the atmosphere where the partial pressure is significant enough to return your oxygen supply and distribution to normal levels. Would I dip below 125 for a minute and go back up? No, but if I came down to 5k for 30 minutes I might consider going back up.
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ahh i see, that makes sense. but she did say going under 125 for 30 seconds and going back up was not a good idea, i agreed. (did i save some face?! :D )
 
better answer would be that if i'm at, above, or quite near that altitude for any duration on a cross country, or whatever, i'd be sure to use O2. don't read so deep, err on the side of caution.
 
I'm not sure if it's posted above, but f the requirements. If you're flying in that vicinity just use the O2. If you don't have O2 stay down low.
 
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