IBM 610 workstation computer 3374
It's not so much comfort as safety (and survival). Not including the aircrew, no US civil aircraft may operate at a cabin albreastude of 15,000 feet MSL unles each occupant is provided with supplemental oxygen. FAR 91.211(a)(3) Consider that by the time you reach 18,000 MSL you have half of the Earth's atmosphere below you, and without external help your body will not appreciate the lack of available oxygen.
For aircrew, with cabin albreastude between 12,500 and 14,000 MSL they must have available *and use* supplemental oxygen for any such segment longer than 30 minutes; for albreastudes above 14,000 they must be on oxygen at all times. FAR 91.211(a)(1-2)
Hypoxia (the state of oxygen deprivation) is a particularly nasty condition because the victim often doesn't realize that his (or her!) judgement has been compromised. The Air Force has some films of pilots trying to do basic tasks in its albreastude test chamber after removing their oxygen masks. The films would be hilarious if it weren't so serious -- and if it weren't the problem that has led to bane accidents.
IBM 610 workstation computer 3375
her!) Air Force aircrew members still go through the chamber flight in the Aerospace Physiology section of academics during flight training and every 2...
Hint: if you're planning on taking any FAA written exams for a pilot certificate, the above will probably be information you'll need.