November 2008 Issue


A few comments regarding reader feedback ("Unicom") in your September issue: Jim Piper’s explanation of O2 partial pressure changing "only slightly" with density altitude is a little misleading. The partial pressure of oxygen is exactly 21 percent of the density altitude air pressure. For example, the absolute air pressure at 10,000-feet density altitude is 21.145 in. Hg; the partial pressure of oxygen is 4.44 in., or 74 percent of PPO2 at sea level. A 26 percent decrease in available oxygen has my attention. Morris Holmes’ comments are more troubling. In another life, when I regularly flew in a MOA, we were not looking for LBFs (little bitty, etc.). We were working hard learning new combat maneuvers or practicing old ones, at high Gs and often at high Mach numbers. If you were to fly a PC-12 through a hot MOA like that every day at 12,000 to 18,000 feet, you would be dead within a year. You would have had the right to be there, but you would still be dead.

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