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.
With an oxygen saturation level below 90 percent, performance and general well-being decreases quickly. As many have experienced over the past 18 months during the coronavirus pandemic, when a person’s oxygen saturation levels drop below 90 percent, a trip to the hospital may be in order. So, if we’re flying around above 10,000 feet for any period of time, we risk having oxygen saturation levels that would normally indicate medical intervention. It’s a sobering thought.
Corporate pilot Daniel Geaslen agrees: “When I flew unpressurized aircraft, I found that anything more than about 20 minutes above 11,000 [feet] left me with early hypoxia warning signs, so I just started wearing [the oxygen mask] at that point. If I ever got above 12,000, I always used oxygen.” And while the physical effects of fatigue, memory loss and malaise are concerning, even more so is the potential for serious confusion and drastically compromised decision-making skills.
John Weisbart, an ATP and CFI with 47 years of experience training pilots in Colorado and owner of Weisbart Aircraft Services LLC, shares a sad personal anecdote. “I’ll never forget the story about [one pilot] from Boulder,” Weisbart says. “He rented my Piper Comanche to fly to Portland[, Oregon,] since his plane was out of service for maintenance. He had tons of time in the make and model, and I agreed to rent to him for this trip if he stayed day-VFR only.
“He ended up departing Boulder midafternoon, said he was picking up another passenger in Wyoming, where he would spend the night then depart at the crack of dawn for Portland. Turns out, he picked up his passenger and decided to press on into the night—into an advancing cold front at either 12,500 or 14,500 feet. Somewhere over Idaho, he lost control of the plane, exceeded VNE, and [the Comanche] broke up in flight, killing all aboard. He had supplemental oxygen onboard but was not using it. The findings of the coroner were that his ascending and descending coronary arteries were 90 percent occluded, meaning that he probably passed out due to lack of oxygen, then fell into the control column putting the plane into a dive. His passengers were unable to control the plane and all perished.
“Moral of the story: No matter how good you think you are, follow the rules. At night above 10,000 feet msl, put the oxygen on—even though [the rules say] 12,500 feet for more than 30 minutes is the requirement. The older you are and the shape you are in weigh enormously on your ability to keep your pulse oxygenation above 90 when operating unpressurized above 10,000 feet at night.”
For such a serious problem, the solution is straightforward, with virtually no side effects other than a small investment. If your airplane isn’t pressurized or doesn’t come equipped with onboard oxygen, you can choose from a number of products that allow you to BYOB. Aerox Aviation Oxygen Systems is among the companies that have expanded their offerings recently. “As a CFI, I now talk to my students a lot about oxygen,” says Scott Ashton, flight instructor and CEO of Aerox. “I find they believe oxygen systems are for much more experienced pilots flying at high altitudes. It can also be intimidating trying to select a system, so they lose out on the benefits of oxygen for the early part of their flying career.”
Ashton had an “aha!” moment not unlike my own that changed his approach to using oxygen—and also fomented his desire a little more than a year ago to purchase Aerox and help deliver more supplemental-oxygen devices to pilots. “I frequently fly long cross-countries—[from the Northeast] to Florida, trips to Oshkosh, [Wisconsin,] etc.—trips that really require long endurance. Until I started using oxygen at lower altitudes, I would always land fatigued and with a bad headache—just generally drained. It took a long time to realize I was actually hypoxic. As students, Part 91.211 altitude regulations are drilled into us, and because of the law of primacy, that is what we remember through our flying career. We are conditioned to think it’s safe to fly without oxygen below 12,500 feet—but it is not safe. The data clearly shows that at altitudes as low at 8,000 feet, pilots can become hypoxic, meaning that we are flying impaired if we aren’t using oxygen. That data was a real eye-opener for me, and I have validated it for my own physiology with a pulse oximeter on many flights since then.”
Use of a pulse oximeter in flight is a great way to assess your actual physiological state, so one should also be part of your flight kit if you regularly fly cross-country at altitudes above 5,000 feet msl. Prices have come down dramatically as a result of the increased public demand during 2020, so you can pick one up at your local CVS or Walgreens for $40.
Pilots may not realize just how critical oxygen is for the proper functioning of the entire body—not just its physical elements, such as visual acuity and the pulmonary and cardiovascular systems, but the mental element as well. “Oxygen is the primary food for the brain, and oxygen levels and cognitive functions are directly correlated,” Ashton says. “By using supplemental oxygen, you are making sure that you are alert and functioning at your best when you need it the most. Shooting an approach to minimums is certainly one of the most demanding things we do as pilots, and after being at altitude for hours, how impaired are we willing to be on that approach? We need to be at our physical and mental peak at the point where we are the most fatigued. Oxygen is the best tool we have to reduce that risk.”
One new product on the scene is Aerox’s PrO2-Plus portable oxygen system for personal use as a backup or for short-term applications. “[The PrO2-Plus] is designed for pilots who want a simple way to have a supplemental supply in their flight bag in case they have to occasionally go up to altitude for weather, comfort or terrain,” Ashton says. “It’s a great entry-level system, easy to use, and the same high quality as the rest of the Aerox product line. We also have a complete line of portable systems for multiple users that have a full set of features like individual flow meters and higher capacities for more-regular use.” The system retails for $399.
Some pilots have taken to carrying inexpensive personal portable oxygen cannisters, such as those used for hiking. These are OK as a stopgap, but they tend not to have the robust aviation-focused capabilities that specialty equipment does from companies such as Aerox, Mountain High and Inogen. That said, there’s no reason you can’t get your portable aviation bottle refilled at any location that fills oxygen bottles; a dive shop or welding supply store work just fine, according to Ashton. For those who want a virtually unlimited source of oxygen, Inogen’s Aviator G5 oxygen concentrator provides a compact 8- or 16-cell-battery-powered compressor that delivers a supply of oxygen-rich air as long as it’s powered.
If you fly pressurized aircraft up in the flight levels, your approach to ensuring proper oxygen saturation uses a different matrix. Monitoring the pressurization system—and being alert to potential malfunctions—can save your life. Also, be aware that the diluter-demand masks in use as emergency equipment on turboprop and jet aircraft need to be maintained properly and replaced periodically. It’s not just for your well-being—it could save your life.
This story appeared in the June/July 2021 issue of Flying Magazine