February 1, 2007
It's safe to say that no aircraft operator would tolerate a critical on-board data-processing unit that was subject to intermittent degradation in accuracy — even downright ill-tempered orneriness. But how about that central organic computer between the headphones that is ultimately responsible for every last detail of the flight?
Pulmonary specialists estimate that several hours spent at cabin altitude — even as low as 6,000 feet — could significantly compromise some pilots' mental acuity. For night operations, U.S. Air Force fighter pilots are advised to use oxygen masks from the ground up because of the physiological effects that can take hold when the cabin altitude exceeds 5,000 feet. Of course the real requirements vary tremendously from person to person — even day to day — but the fact remains that even pilots of some pressurized aircraft could be putting their gray matter at risk when they can least afford the degradation in performance.
The FAA rules on when and where to use oxygen are much more black and white. Pilots — at least those who recently passed their written exams — are familiar with federal aviation regulations regarding requirements for supplemental oxygen in nonpressurized aircraft and for emergency oxygen in pressurized airplanes. But more and more pilots, especially as they reach AARP-eligible age, are discovering that a few hits of pure O 2 before a complicated approach at the end of a long flight can bring the whole world into sharper focus, especially at night. One Bonanza pilot, writing in the American Bonanza Society's magazine, said he includes a few deep breaths of oxygen as part of his pre-approach checklist.
Like many FARs, the rules involving oxygen requirements are aimed at preventing catastrophe. But what about effects that aren't as immediately dramatic, but which could lead to slow-acting degradation of performance, especially over long periods of time? That call is left up to each individual pilot's good judgment.
Before anyone at the FAA — or Congress — becomes too alarmed and starts drafting new FARs, it's important to note that the need for supplemental oxygen is, indeed, highly variable from person to person and from situation to situation. A friend who is a Beechcraft A36 Bonanza owner told me he has tried using his supplemental oxygen system a few times after long night flights at midaltitudes, having heard that it makes approach lights get brighter and otherwise dramatically improves night vision. "It just never happened," he said.
My friend is a trim, fit, tobacco-free pilot. Conversely, those who smoke and are overweight are intrinsically more vulnerable to the effects of altitude than an aerobically fit pilot. A recent Sporty's Pilot Shop catalog featured supplemental oxygen systems and a story involving a 50-something, overweight Piper Arrow pilot — a smoker — who was temporarily blinded by hypoxia on a solo flight at 8,500 feet on a sunny afternoon. He was lucky to survive.
But it's not just extra pounds, nicotine addiction, and an aversion to physical activity that can cause trouble. A few martinis the night before, lack of sleep, or a nagging flu can place even a dedicated denizen of the gym in jeopardy, while the well-rested doughnut aficionado in the right seat may be good to go.
Clearing the morning-after head with an oxygen infusion — for whatever reason — is a time-honored practice, usually spoken about in subtle tones.
A product marketing manager for FlightSafety International (FSI) at Teterboro, New Jersey, said, "Ex-military pilots talk about 'in the day' when they would have a few drinks the night before and breathe in some oxygen before launching on a mission the next morning." Using oxygen as a hangover cure goes back much further. Royal Air Force pilots during the Battle of Britain in 1940 were known to stick their snouts into their masks before the first flight of the day after a long night in the pubs — or at least hang their faces outside the cockpits of their Spitfires in the prop wash, the better to turbocharge their bloodstreams with more oxygen.
Besides the oxygen-sapping effects of demon rum, there may be less easily identifiable elements such as heredity, stress, and biorhythmic cycles that can have an effect. It all relates to how the human pulmonary system works.
Without delving too deeply into medical text, let's begin by saying that the heart, brain, eyes, and other organs need oxygen to perform. We pass that oxygen into our lungs to be delivered throughout the bloodstream by hemoglobin, an iron-protein compound found in red blood cells. Oxygen attaches to hemoglobin and is carried throughout the body through our arteries.
The average person breathes 3,000 gallons of air per day, including 600 gallons of oxygen. Each of some 25 trillion red blood cells in the body can carry about four molecules of oxygen for delivery throughout the bloodstream. After dropping off their oxygen molecules at the appropriate waypoint, the red cells don't make the return leg alone. They come back to the lungs carrying carbon dioxide for exhalation. The brain consumes 20 percent of the oxygen used by the body, most of it going to the cerebral cortex, which controls judgment, among other personality attributes.
There are two ways that this arrangement can be sabotaged. The amount of oxygen in the air we breathe can be diminished, or the capacity of the hemoglobin to carry its fair share of oxygen can be compromised.
Even a crowded, stuffy room with poor ventilation can lower the level of ambient oxygen. As everyone breathes and exhales, the percentage of oxygen in the air constantly decreases. That may be one reason why your colleagues' judgment appears to deteriorate over the course of long staff meetings (while yours remains razor sharp, of course).
Every pilot knows that altitude has the same net effect, even without all the corporate hot air. Atmospheric pressure at 18,000 feet is half that at the surface. Although actual air pressure and oxygen content at 12,500 feet might vary somewhat based on density altitude, there is little enough variation that the FAA is confident it can accurately calculate where pilots and passengers ought to start using supplemental oxygen.
What is less consistent are the characteristics of individual physiology. Although we know that good aerobic health is a positive influence, there is medical and anecdotal evidence to suggest that lesser-known factors can come into play, including gender.
Research shows that women appear to be more susceptible to effects from low oxygen than men. Scott Philiben, vice president of engineering and business development for oxygen-system vendor Precise Flight in Bend, Oregon, says, "It's just basic physiology; women have lower concentrations of hemoglobin than men."
He said he has heard story after story from idyllically matched flying couples who never argued on the ground, but became irritable and touchy with each other after long flights at altitudes as low as 6,000 feet. In most cases, he said, the woman would be the first to experience headaches and other symptoms of hypoxia, including nausea, dizziness, and what researchers refer to — politically correctly — as "personality change."
It's not that men are unaffected; it just seems to take them longer to get the symptoms. "The guy will be sitting there saying, 'I'm fine up here. What's your problem?' while she's feeling more and more miserable. Not a good situation," Philiben says.
As if to even the score between the sexes, glider-enthusiast Philiben said he had an illuminating experience with a flight at relatively low altitude. He said his performance during flight training was always a bit rough around the edges, which he had always attributed partially to lack of talent, and partially to his instructor who was known for his ill temper and would quickly lose patience with his students' ham-handed flying. One day, Philiben decided to use one of his training flights to test a new two-place oxygen system. He said that, with oxygen, not only did his control coordination improve markedly, but also his instructor was much calmer.
So glider and piston pilots are recognizing that oxygen could be an avenue to improving their flying skills — if not their marriages. For those who haven't tried it, it could be worth renting or borrowing a portable oxygen system for the next long cross-country trip or two, just to check it out. But how about those flying sophisticated pressurized airplanes — even jets — aloft high in the flight levels?
As most know, aircraft pressurization systems pump up the cabin so its occupants can breathe normally at high altitude with low ambient air pressure. But most aircraft pressurization systems can retain a "sea level" cabin only so high. Some systems, including those installed in Cessna P210 piston singles and early Beechcraft King Air turboprop twins, have maximum pressure differentials of about 3.5 pounds. The "cabin altitude" can reach 8,000 feet when the actual airplane is as low as the midteens. So those pilots — and their passengers — might be pushing the limits of their physiology on a long flight. Low-grade symptoms of hypoxia might even touch those flying corporate jets, whose cabin altitudes may reach 8,000 feet during long segments of cruise flight in the high flight levels.
Asked about corporate crews and supplemental oxygen, an FSI instructor on the Bombardier Global Express at the Wilmington, Delaware, learning center said that in the several years he had instructed and flown the Global Express, the subject had never come up in conversation. He said the Global Express has a maximum cabin altitude of 7,230 feet at 51,000 feet msl, most flights are conducted lower with cabin altitudes never exceeding 6,000 feet.
The instructor said the Global Express and some other business jets are equipped with "cruise masks," which make it easier for pilots to dip into some oxygen if the spirit moves them. The regular emergency masks can be difficult to stow after use, making them less attractive for impromptu, supplemental use. "The cruise mask is meant for safety, at altitude, when the second pilot leaves his seat." But, he said, the cruise mask would make a handy source of oxygen near the end of a long flight, "about 20 or 30 minutes before starting the descent for landing. It certainly wouldn't hurt."
The instructor added that he has experience in mountaineering and recognizes that some people cope with altitude better than others. "Some have problems with headaches and dizziness at 10,000 feet, while others can climb Mount Everest [29,035 feet] without oxygen. At the very least, it's a useful topic for discussion."
Whether it's a corporate jet crew in the high flight levels or a piston pilot on a long cross-country jaunt, some experimentation with an oxygen system might prove illuminating. It could mean even more than a simple personality upgrade. It is possible that long hours at relatively high cabin altitudes — particularly for sea-level-based pilots — could have been a factor in some fatal crashes that involved the pilot's otherwise-unexplained poor performance and questionable judgment. We'll never know whether a few lungfuls of canned O 2 might have at least interrupted or slowed the chain of events that led to disaster.
Mark Phelps is a private pilot living in Basking Ridge, New Jersey, and owner of a 1954 Beechcraft Bonanza.
Jack R. Byrd, AOPA 562674, a commercial instrument-rated pilot who has been flying for more than 30 years, frequently flies with his English Pointer bulldog, Buck, in Byrd's turbonormalized A36 Bonanza. Byrd wanted to find a safe way to provide Buck with oxygen when he flew on extended trips at high altitudes. He designed and built an oxygen system for the dog that has been tested and routinely used for more than two years. Byrd's research, findings, and advice on how to build and use an oxygen system for pets can be found on AOPA Online.
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