BREATHE EASY AT ALTITUDE

What do you need when it comes to aviator’s oxygen?

- Julie Boatman

I was having the time of my life: We were traveling home to the Boulder Municipal Airport following my first mountain checkout back in 1992, and I was on my way to a commercial pilot certificate. But more so than that, the peaks and vistas west of the Front Range of Colorado beckoned.

My instructor put on his oxygen mask as we approached the Continental Divide, but we would spend only a few minutes between 12,500 and 14,000 feet. I felt great, so I didn’t see the need for it—a mistake we both made. With me developing the tiniest of headaches, we descended from 13,500 feet to the traffic-pattern altitude at what was then 1V5 (6,100 feet msl and 800 feet agl).

I made three landings that day: the first on purpose, then the second and third as I bounced from misjudging my round-out. Hypoxia hit me harder than that touchdown, and I was fortunate that my poor landing was the only result.

I was in my early 20s, in good health, and acclimatized to life in mile-high Colorado, but none of those things precluded me from feeling the direct effects of hypoxia below the maximum legal limits. As it turns out, my experience was common—and the result of a general lack of understanding about how insidious hypoxia can be.

The Flight Safety Foundation has released data that illuminates the issue. The key metric to track is the oxygen saturation level within the blood’s O2- carrying hemoglobin. As ambient air pressure drops with altitude, the partial pressure of oxygen decreases along with it. While the human body generally compensates fairly well for this reduction at altitudes from 5,000 to 7,000 feet, above that, the risk rises sharply—especially once you reach about 10,000 feet. A pilot’s oxygen saturation runs at roughly 98 percent at sea level, decreasing to about 90 percent at a point between 7,000 and 10,000 feet, depending on the specific environment and pilot’s physiology.