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High Altitude Depressurization

The tragic loss of pro golfer, Payne Stewart and five others aboard Stewart's Learjet 35 has raised many questions. There seems to be little contention that the crew and passengers of that fateful flight suffered from the effects of hypoxia. (I'll explain why in a minute.) If this theory turns out to be true, what seems to have many people puzzled is how such a thing could happen.

For those of you that aren't familiar with hypoxia, this is the term used to describe the physical effects of the lack/loss of oxygen in your body. To quote the AIM (Airmen Information Manual), "Hypoxia is a state of oxygen deficiency in the body sufficient to impair functions of the brain and other organs."

Contrary to common belief, high altitude hypoxia is not caused because "there's less oxygen available at high altitudes." The truth is the ratios of oxygen to other natural gases are essentially the same at high altitude as they are down at sea level. What is different is atmospheric pressure is lower at high altitude. (As you'd expect, atmospheric pressure decreases as altitude increases.)

What happens at high altitude is pressure decreases to the point where oxygen cannot penetrate the membrane of your lungs (where the transfer of oxygen and carbon dioxide takes place). Although CFR 91.211 (Code of Federal Regulations - - still commonly referred to as the FARs) requires the use of supplemental oxygen to be used as low as 12,500' MSL (Mean Sea Level), the effects of hypoxia can be observed as low as 5,000' MSL.

The thing that's led experts to believe that Stewart's Learjet may have had suffered from depressurization was observed by the military fighters that intercepted the un-responding aircraft. The pictures taken of the aircraft clearly displayed the windows of the Learjet were fogged/iced over. This is a typical sign and characteristic of high altitude depressurization. And depressurization at those flight levels would surely lead to hypoxia unless supplemental oxygen was available and continuously used.

My experience with high-altitude depressurization is very limited (I've never experienced it), so please allow me to direct you to some of the experts. Here's a link to where you can read all about high alt depressurization. This informative article explains why simply "holding your breath" wouldn't be enough to dramatically change the very short period of consciousness (about five seconds) that you'd be afforded in such conditions.

1999 Ben Chiu

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