NewsWordy is right: It’s all about individually physiology. At 23 I flew a 172 at 15,500 from Minneapolis to DC without oxygen or symptoms. Now, and with a military aviation history, I KNOW how to recognize hypoxia, and at age 71 and at 15,500′ I WILL experience symptoms without supplemental O-2.

Pilots who fly in the hypoxia zone SHOULD take a potentially life-saving course in an altitude chamber – my first “ride” I had no clue about the symptoms, and “woke up” protesting I didn’t need the mask yet. It was not until I looked down at what I was writing during the exercise that I realized just how unconscious I had become. We were then trained on the various hypoxia symptoms and how to recognize our own individual symptoms (which now I can do).

Pilots who fly in the hypoxia zone should ALSO learn that there is a way to (at least temporarily) reduce hypoxia with a personal pressure-breathing exercise. Take a deep breath, and hold it while hunkering down (trying to exhale while still holding your breath), and repeat 8-10 times a minute. It will force more oxygen into the bloodstream – but it’s not something you can do for an extended period of time. It’s an emergency procedure to allow you to correct the oxygen problem, and it could buy you some desperately-needed minutes.

In a hypoxic state, breathing faster not only doesn’t work, but also is likely to be dangerous. The human body has evolved in a way that natural breathing rate is attuned to the carbon dioxide in one’s blood, not the oxygen level. Breathing faster helps eliminate CO-2, which then tells the body to breathe slower (at a time when blood-oxygen levels can be dangerously low). It’s called “hyperventilation”, and in a high altitude setting that can be deadly.

For those of us who like to fly in the hypoxia zone, learning to recognize and deal with hypoxia is a potentially life-and-death skill. Even with that skill, I plan to acquire a pulse oximeter, because I plan to keep flying high (no, not in that sense) for a very long time.

Pulse oxymeters are a must have if flying where oxygen “might” be needed. When the FARs were written these devices were not generally available but they are now and the rule is about as useful as the 180 lb person (for W&B). I just bought a second unit for $30… my primary is one I wear on my wrist and can continuously monitor my sats. I’d strongly recommend that is SOP and meter your oxygen accordingly. You will learn what your body needs and eventually how to listen to it and know before you look at the pulse oximeter how you are doing.