A mantra in pilot training is that you should train the way you fly, and then fly the way you train. Thanks to its enormous fleet of Level C and D full-flight simulators, FlightSafety International has been providing absolute realism in flight training for many years, except in one area-high altitude physiology. Until now, the only training FlightSafety and other schools could provide is classroom education about the effects of high altitude on the body and pilot performance. Now, for the first time, pilots can safely experience real hypoxia in a flight simulator without leaving the ground.
FlightSafety has teamed up with the Mayo Clinic to create a device that changes the mix of nitrogen and oxygen in the air a pilot breathes to exactly simulate the effects of high altitude physiology. The Mayo Clinic has a long history in the study of flight physiology, dating back to the 1930s. The clinic was among the first medical facilities to use supplemental oxygen to treat patients. That work, plus an intense interest in aviation by its founders, led the clinic to the study of high altitude pilot physiology and development of some of the first effective oxygen masks for pilots. During World War II the clinic built the first centrifuge to study the effects of G-loads on pilots, and that led to the invention of the G-suit that squeezes the lower body, and the straining maneuver that helps pilots combat the debilitating effects of Gs.
The Mayo Clinic also built the first altitude chamber to create a high altitude atmosphere on the surface. Air is pumped out of the chamber to create the thinner, less dense atmosphere of flight. The chamber works well as an altitude simulator, and it has, until now, remained the primary training device for pilots. All military pilots, and many civilians, who have been in the chamber experienced the effects of high altitude without supplemental oxygen, and been better for it.
However, the altitude chamber has several serious drawbacks. Because of the size and weight of a chamber, only a comparative handful have been built. The chamber is totally artificial and absolutely nothing like an airplane, except for maybe the oxygen masks the pilots don after experiencing hypoxia. And there is a small risk of physical harm to people inside the chamber as the pressure changes. Most injuries are relatively minor problems with ears and sinuses, but there is the rare but real possibility of significant damage to the central nervous system.
Way back in 1936 doctors at the Mayo Clinic realized that they didn’t need to always use the altitude chamber they had invented to create a realistic altitude simulation for pilots. Instead, by changing the percentage of nitrogen and oxygen in the blend of gases a pilot breathes through a mask, the lungs will behave exactly as they do at high altitude without the risks of big pressure changes on the rest of the body. The clinic called this technology a “mixed-gas paradigm.” The U.S. Navy and the Mayo Clinic hold patents on the technology and FlightSafety has worked with both to make the training available to all pilots.
As you may remember from high school biology class, the atmosphere is made up of approximately 21 percent oxygen, 78 percent nitrogen, with the remaining one percent consisting of a bunch of other gases. This ratio of gases remains the same throughout the atmosphere, but the pressure of the combined gases decreases with altitude. It is the change in atmospheric density and pressure, not a decrease in oxygen percentage, that affects people at high altitude. At 18,000 feet the atmosphere is about one half as dense as at the surface. The atmosphere density decreases exponentially above that, along with the pressure of the gases.
Our lungs operate by exchanging oxygen in the air we breathe for exhaust gases through a membrane. The lungs depend on the pressure of the gas in the lungs to push oxygen through the membrane. When the pressure of the air we breath drops, the pressure of the available oxygen molecules also decreases, so the pressure on the part of the intake gas that is oxygen goes down. This so-called partial pressure of oxygen explains why the lungs can’t absorb the needed amount of oxygen at high altitude. There simply isn’t enough pressure in the available air to push the necessary amount of oxygen across the lung membrane and into the blood stream. When we don an oxygen mask we increase the percentage of oxygen in the gas entering our lungs, and thus the “partial pressure” of the oxygen is similar to that of a lower altitude.
The mixed-gas hypoxia simulator reduces the partial pressure of the oxygen by adding in more harmless nitrogen to the gas delivered to the pilot’s mask. Without changing the total pressure of the surrounding atmosphere at the surface, the simulator delivers the same oxygen partial pressure a pilot would experience at high altitude. There is no risk of pressure changes on the rest of the body, but the lungs behave exactly as they would at altitude, and thus the brain doesn’t receive enough oxygen and the effects of hypoxia begin.
Many of us have seen films of pilots in altitude chambers flailing about, unable to put on the oxygen mask on command. That’s interesting, and perhaps useful as a scare tactic to remind us all that hypoxia can be deadly. But that kind of “training” is useless in the real world because the pilot in the demonstration is unable to save himself, much less his crew and passengers.
FlightSafety, and any sane pilot, have no interest in how a pilot fails when deprived of oxygen to the point of uselessness. We know what happens then. What every pilot needs to know, and what FlightSafety’s new training teaches, is how to recognize your own individual early symptoms of hypoxia so that you can take immediate action before the inevitable happens.
The FlightSafety course begins with about two hours of classroom instruction on all aspects of high altitude physiology. Included in the material are the common subjective symptoms of hypoxia, such as euphoria, lightheadedness, dizziness, blurred vision, tunnel vision and so on. Those are some of the symptoms the hypoxia sufferer will experience. The objective symptoms, the ones that can be measured, are poor judgement, mental confusion, cyanosis (turning blue), loss of muscle coordination, euphoria and finally unconsciousness.
The classroom materials are complete, and before FlightSafety’s new hypoxia simulator was available, were the totality of high altitude instruction. We all learned what may happen to us as our body is deprived of enough oxygen, but we never knew what symptoms would hit us first, and how they would actually feel. FlightSafety has just begun to offer the hypoxia simulation at six of its larger training centers. The partial-pressure gas device is plumbed into only one simulator at each center, so the training may not be in exactly the same model airplane that you fly, but it is in the same category. I experienced the training at the Falcon Jet center at Teterboro where the Falcon 50 is used.
The hypoxia awareness training is conducted in two phases. The first is a non-flying experience to teach you to recognize your own individual early symptoms of the onset of hypoxia, and the second hypoxia experience occurs while actually flying the simulator through normal maneuvers, concluding with donning of the masks and an emergency descent.
The mixed gases are delivered to the pilot through a tight-fitting medical type of mask. The mask was not uncomfortable for me and though it’s not totally natural, it did not interfere with my pilot performance in any way, except that my reading glasses perched a little higher on my nose.
To keep track of your body’s reaction to the simulation, the FlightSafety instructors put a pulse oximeter on your finger tip to measure the saturation of oxygen in your blood, and your pulse. The oximeter is commonly used in hospitals to monitor patients, and some pilots use them in unpressurized airplanes to warn of hypoxia. That may make sense, but only after you have been through FlighSafety’s training, because what you will learn is that every individual responds differently to blood oxygen saturation levels. The oximeter FlightSafety uses is the remote type. Only the tiny sensor and its wire are attached to your finger tip so it does not interfere with your flying ability. I won the coin toss and went first, with my copilot, Frank Yakutchik, a highly experienced pilot and corporate flight department manager, in the right seat to observe. My oxygen saturation level was 99 percent at the start of the training, a perfectly normal reading for the near sea level elevation of Teterboro.
The partial-pressure gas simulator increased the effective altitude of the air reaching my lungs at about 10,000 feet per minute to an altitude of 22,500 feet. FlightSafety, working with the Mayo Clinic, has selected that altitude because it is safe and causes the onset of hypoxia symptoms at a level where they must be recognized by a pilot so he can take action.
The instructor monitors the drop in blood saturation while asking you questions about how you feel. While experiencing the high altitude I worked on basic cognitive problems such as serial subtraction of seven from 1,000 and writing the results in four columns, drawing a clock face with a time specified by the instructor, and also writing down any symptoms I experienced.
To my surprise, the symptoms I felt were mild. The first thing I noticed was that my vision was a little fuzzy, and I wrote that down. Then I began to feel a little lightheaded, but not dizzy. I wrote that down. There was also a strange, warm feeling in the back of my neck. Finally, there was just an overall sensation of labored breathing, and an odd feeling in my chest. I just didn’t feel right, but it was not an overwhelming sensation. FlightSafety limits the time at 22,500 to under seven and a half minutes, but most pilots so far have recognizable symptoms in under five minutes. After about five minutes at the simulated high altitude, the air I was breathing was switched to 100 percent oxygen. Recovery was very rapid, and it was then that I noticed the color wheel brighten up. I had noticed that the colors had lost their distinction while at the simulated high altitude, but with oxygen back, the difference was sharp.
The subtle nature of my symptoms was revealing, and the most important part of the training. My blood oxygen level, which was constantly monitored and recorded by the instructor, had dropped to 76 percent, a significantly low level that was undoubtedly degrading my performance, but I felt little. FlightSafety has noted that some pilots detect symptoms with blood saturation levels in the high 80 percent range, and that’s good because they are warned at a greater margin before useful consciousness ends. There is no uniform blood saturation level that indicates the end of useful consciousness, but anything around 50 to 60 percent will almost certainly do it. There is no large body of data on blood saturation versus pilot performance, because until now, training had been limited to altitude chambers and blood saturation of those in the chamber was not routinely measured. As FlightSafety trains more pilots, patterns will certainly emerge, but it will also show how impossible it is to generalize about the onset of hypoxia in individuals and what the symptoms will be.
After my blood saturation level had returned to 100 percent, which didn’t take long, the second phase of the training, the flying portion, began. The instructors set the simulator in cruise with everything normal. I was instructed to climb to a new, higher altitude and given vectors to follow. What I didn’t know was when the instructors would use the partial gas pressure simulator to raise the altitude of my lungs to 22,500 feet. Unlike the first phase when I knew that I would be subjected to the high altitude almost immediately, in the flying portion I had to both fly, and be aware of onset of the symptoms I had experienced earlier.
After several minutes of normal flying, and normal feeling, I began to notice the same sensation of labored breathing and the odd abnormal feeling in my chest. I was pretty sure that my blood saturation level had dropped. My flying was still okay, but I began to notice that I couldn’t scan the instruments normally. When I looked at the altimeter, it took a couple seconds to focus on it and understand its indication. My vision was slightly blurred and I was beginning to tunnel in. And my thought process had slowed considerably. At that point the instructors simulated a cabin decompression with the warnings and the cabin altitude indicator climbing. I took off the high altitude simulator mask and donned the airplane’s normal quick don mask, as did my copilot, and began an emergency descent. The hypoxia symptoms disappeared almost immediately with the oxygen mask on, and the descent and landing felt perfectly normal. My blood saturation level had dropped into the low 70 percent range and my pulse had increased from the 70s to the 90s.
What FlightSafety has already learned in developing the course and testing it on a variety of pilots is that experienced pilots continue to fly well and ignore hypoxic symptoms compared to the stationary exercise. Flying skills apparently become ingrained and we are able to continue to perform normally despite greatly diminished faculties, which in this case is a problem, because we are not thinking clearly and will certainly make bad decisions. That’s why the initial stationary phase of the training is crucial to identify symptoms that we, as pilots, would almost certainly ignore if we experienced them first in flight.
We then changed seats and Frank did the altitude training while I observed. Frank had almost no symptoms during the stationary phase of the training. He did a good job with the subtraction problem, okay with the clock, and kept saying he felt normal as his oxygen saturation dropped. Finally, Frank just went quiet, not saying anything, and not working on the problems. When the instructors asked him how he felt, he said fine, but obviously wasn’t. When the 100 percent oxygen was introduced Frank experienced a mild form of the “oxygen paradox,” with his symptoms momentarily getting worse before recovery. This is a documented reaction in some people, but as with all things about hypoxia, every individual is different.
During the flying portion Frank did a perfect job of handling the Falcon, even flying the 45-degree steep turns with enough precision to easily pass a checkride while hypoxic. But, like me, he had noticed the odd feeling in his chest on the first phase, and felt it again in flight.
We both agreed after the training that our own symptoms of the onset of hypoxia are much less dramatic and noticeable than we expected. We both have been flying high altitude airplanes for decades, and have been through high altitude physiology courses many times. But the description of the possible symptoms didn’t match either of our realities. It’s not the fault of the classroom information, it’s just the nature of hypoxia.
The hypoxia course is so new that FlightSafety hasn’t yet developed a recommendation of how often, if ever, the training should be repeated. After the experience, I think I would benefit from taking the course a couple more times during annual recurrent training. I think repeating the course would be like grooving a golf swing. Everything about the hypoxic experience is so new, and so unexpected the first time, that it can’t all possibly sink in. I think the next time I will be more attuned to my own personal symptoms and will be able to recognize them more clearly. Frank signed up his entire pilot roster for the training, as have the few other chief pilots who have had the experience.
Most attention in both airplane certification and pilot training has been focused on a sudden cabin decompression and the very real emergency that creates. Sudden decompressions are rare, and pilots have actually done a good job of handling the few that have occurred. The accident record shows the greater threat is the subtle loss of pressure-sometimes caused by the cabin never pressurizing-that is the situation pilots have not handled well. And after FlightSafety’s training, I now know why. My own early symptoms of hypoxia are so mild that I am convinced that before this training I would not have accurately detected them in time to make good decisions. Now I have a chance.
A very real safety threat for a well- trained crew has now been addressed in a realistic and useful way. In fact, the hypoxia training will be a part of the standard in the Citation Mustang, which is expected to be flown mostly by single pilots, many of them owner pilots with little or no previous jet experience. The training will be important in the Mustang, but I think it is essential for any pilot. There is always a cure available for hypoxia in any airplane if the pilot recognizes the onset in time. Just as we all learn to identify an impending stall, we need to know when our own body is approaching the failure point in time to take action. Thanks to FlightSafety, we can train the way we fly, and fly the way we train in terms of personal high altitude physiology, the last area I can think of where realistic training has not been available.
