Oxygen-System Primer

For years, I happily flew along at high altitudes — often at night — without much regard to the dangers of hypoxia. After all, I was young, in decent shape, and wasn't exactly exerting myself while droning along monitoring the progress of my flight plan as well as the airplane's systems. My attitude changed markedly the first time I brought a portable pulse oximeter along on a flight from Wichita to Maryland. In fact, what I saw scared me a little. Hypoxia was always a lot closer than I thought. And it may be for you, too.

As most of us know, the oxygen at altitude is plentiful; unfortunately, the pressure required for our bodies to absorb it is not. Supplemental oxygen helps, but it's not a perfect mousetrap, especially at altitudes above 25,000 feet where the system may not be able to keep up. Unfortunately, one of the most insidious side effects of hypoxia is the feeling of euphoria. "Everything feels great," "What could go wrong?" and "I feel fine" are all phrases that may swim through the head of a pilot happily tooling along at the FAR-mandated, no-oxygen-required altitude of 12,500 feet. Depending on the pilot, he could be "just fine." I learned, however, that I'm not one of those pilots.

Pulse oximeters

My flight from Wichita started at 9,500 feet VFR. Since I was to attempt a nonstop flight home, I was planning to be at that altitude or higher for more than four hours. I thought the pulse oximeter would be a prudent tool to have as well as my portable oxygen bottle. Modern pulse oximeters are quite simple and small. Just clamp the gadget to the end of a finger and it does its thing. On the ground, near sea level, my resting pulse is about 65 beats per minute and my oxygen saturation level is usually 99 to 100 percent. At 9,500 feet on my trip from Wichita, however, my heart was beating at 100 beats per minute, and all that pumping was only yielding an 89-percent oxygen saturation level. I always attributed headaches when flying to cockpit noise or my headset. More likely, however, the headaches were a result of oxygen deprivation. This level of heart rate also explains why I was often exhausted after a flight. That heart rate for me is more like a light workout for as many hours as I was flying.

Many doctors recommend going on oxygen when saturation levels dip below about 90 to 92 percent. Depending on the person, hypoxia starts at a blood saturation level of 80 to 85 percent. On my flight, I strapped on the cannula and things looked much better — almost normal — on the pulse-oximeter readings within a minute or two.

At night, the concern grows because of how much our eyes depend on oxygen to function properly. In fact, night vision begins to deteriorate at altitudes as low as 4,000 feet when you don't use supplemental oxygen. Although you may not be high enough to reach blood saturation levels that would cause hypoxia, you should consider your ability to see clearly a determining factor as to when to begin using oxygen while flying at night.

Either purchase or borrow a pulse oximeter and carry it with you on a few flights to see how your body is affected by altitude. Aside from the occasional headache, I "felt" fine for all of those years I plodded along at altitudes as high as 12,500 feet for hours. Throw an emergency or a distraction into the mix and I might have been asking too much from my heart to supply my brain with adequate oxygen. Most every company that sells oxygen equipment sells pulse oximeters. The cheapest can be had for less than $200 and does not require a prescription.

Bottle to go

The least expensive way to get oxygen in an airplane, if the airplane is not pressurized or equipped with a built-in tank/regulator system, is a portable system. Depending on the size of bottle and number of ports, you can obtain a quality portable oxygen system for about $500 from a number of manufacturers and pilot supply shops. Portables can be outfitted with regulators to supply a constant flow of oxygen to as many users as you wish. Of course, the more users in the loop, the faster you'll use up your oxygen. Plug in six masks to a small bottle, and you'll use up your supply, pronto.

There are two solutions for this dilemma. Get a bigger bottle and/or utilize demand conservers or flow meters. Demand conservers are devices that slow oxygen consumption by more precisely measuring the flow rather than delivering a constant flow. Some utilize check valves that stop the flow of oxygen when you are exhaling, vastly slowing the consumption rate. Although these devices will cost some extra bucks, they will pay off in reducing the amount of bottle refills, which at some FBOs can be pricey.

Masks or cannulas? Which do you need? Depends on how high you want to fly. Cannulas can be more comfortable and generally considered safe to use up to 18,000 feet. There are also clever cannulas sold by Rocket Engineering and Sporty's Pilot Shop built to work with your headset. Masks are good to 30,000 feet but are much more cumbersome and make radio communications more difficult. No matter which you choose, it's always a good idea to make sure there are no kinks in the tubing that may block flow. Most aviation masks and cannulas have a flow meter in the line. A periodic check of the green flow detector should be part of your regular scan.

Built-in bottles

Many airplane models are already equipped or can be easily equipped with a built-in oxygen system. Aside from pressurization, this is the most convenient way to get oxygen to you and your passengers. Simply plug in a mask or a cannula at your seat, check the flow gauge in the tubing, and breathe normally. The large bottles used in built-in systems generally last a long time, especially if you are using oxygen conservers. Just make sure the bottle is turned on before you depart. The crash of a Lear 35 carrying golfer Payne Stewart was attributed partially to the fact that the oxygen bottle was turned off.

But even if you're lucky enough to have a pressurized airplane, you wouldn't be doing yourself a favor by storing your portable oxygen system on a shelf in the hangar. I recently flew a Royal Turbine (a Beech Duke converted with turboprop engines) and quickly realized the value of supplemental oxygen, even in pressurized airplanes. As fine an airplane as the Royal Turbine is in nearly every category, it was wheezy in the pressurization department. At its ceiling of 28,000 feet, the cabin of the Royal Turbine is 12,500 feet. Even a relatively short trip at that altitude can be hard on the pilot and passengers. If I were lucky enough to own one, I'd be plugging in a cannula on every flight where cabin altitude went over 10,000 feet.

In addition, engine failures in pressurized airplanes signify a serious emergency if you are already at altitude. In a twin you lose half of your pressurized air source and in a single, you'll lose it all. Single or twin, the cabin will start climbing immediately. Time to don the masks and get to a lower altitude.

If you plan to fly above 6,000 or 7,000 feet for more than a few hours, you'd be doing yourself a favor to gauge your altitude tolerance with a pulse oximeter. If you're like me, and find that you're not as well off as you thought, start pursuing avenues of getting supplemental oxygen in the cockpit. Your flying will be safer, more precise, and therefore more enjoyable. After landing, you'll likely feel more refreshed and headache free. It would be a shame to simply limit your flying to the lower altitudes because of the need for supplemental oxygen. Most airplanes hit their peak efficiency in the 7,000-to-11,000-foot range and the rides are often smoother and above most fair-weather clouds.

Pete Bedell is a first officer for a major airline and former technical editor of AOPA Pilot. He is type rated in the Boeing 737, Canadair RJ, and BAe Jetstream 41. He is a co-owner of a Cessna 172 and Beech D55 Baron.