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Normally 10,000 ft is considered safe altitude for emergency descents and 12,000 ft a maximum that can be flown in unpressurised aircraft without using supplementary oxygen.

But when flying in the mountains with a crew that normally lives at say 5,000 ft or more, can they afford higher altitude? And by how much?

Note: The 12,000 ft I've seen somewhere, but I don't know whether it is actually a regulation or just recommendation.

Jan Hudec
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  • I've gone flying after spending a week skiing between 10k and 12k feet and I certainly felt like I could spend all day at 15k without O2. – casey Jun 19 '15 at 06:09
  • Is there a legal limit to fly unpressurized aircraft? – vasin1987 Jun 19 '15 at 10:19
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    @vasin1987 yes, not to fly, but to fly without supplementary oxygen. – falstro Jun 19 '15 at 12:36
  • @falstro yeah that would be a good answer here. However i guess OP expect the answer where no supplementary oxygen is requireed. Ie can pilot get used to high altitude that lack of oxegen is not a problem. Hmmm i wonder what answer this question gonna get :) – vasin1987 Jun 19 '15 at 12:46

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Yes, maximum possible altitude at which a pilot can fly an Unpressurized Airplane without the need for supplementary oxygen does increase with acclimatisation. But the international aviation laws do not take this into account and hence they have a general altitude limit for unpressurized flying without supplementary oxygen.

Victor Juliet
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  • Do you have a reference for what that limit is? – Jan Hudec Jun 19 '15 at 14:55
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    @JanHudec Not sure about ICAO's model regs, but for the US it's FAR 91.211: Supplemental oxygen is required for crew if you're above 12,500 feet for more than 30 minutes, or if cabin altitude is above 14,000 feet for any length of time. Above 15,000 feet it's required for everyone onboard. (There are other requirements that come into play if the aircraft is pressurized.) – voretaq7 Jun 19 '15 at 20:48
  • Since the question talks about emergencies and mountain flying, I think it'd be appropriate to add that in emergencies, rules come second while safety comes first (as described in FAR/AIM §91.3(b)). – Maverick283 Jun 20 '15 at 13:40
  • @Maverick283: Actually, no, the question does not talk about emergencies. – Jan Hudec Jun 21 '15 at 14:10
  • @janhudec alright, it is talking about a "emergency descent"... I'd still count that as an emergency though?! – Maverick283 Jun 21 '15 at 18:17