How an Hour in a Fart Chamber Saved My Life

There is a lot more to being a pilot than having the stick & rudder skills to keep the ball centered and the blue side up. Sometimes I think we don’t emphasize these skills enough. How are you going to go to the bathroom on this flight? What are you going to eat? (You did remember to bring some food, right?) Do the tone of your radio voice and efficiency of your calls inspire confidence in controllers, or do they earn you disdain and penalty vectors?

I recently used another skill, recognizing my personal hypoxia symptoms, to potentially save my life and my airplane. I learned that skill through several sessions in flatulence-filled funny rooms, also known as hypobaric (or "altitude") chambers. How about we mix it up today and do story first, background second?

My 1950 C-170A, N5792C, had spent several months stranded at Stinson Field in San Antonio, TX. (GateOne Aviation, the new FBO at KSSF did a great job with the annual inspection.) I finally got a combination of a few free days and some decent weather, so I hopped a flight to San Antonio. I was airborne in N5792C within 90 minutes of landing at KSAT...impressive!

It was a gorgeous day and the sky was filled with widely scattered fair weather cumulus clouds. I like to fly high, especially in the summer. It’s cooler, there’s less turbulence, and it saves fuel. I caught a few east Texas thermals, climbed to 9,500’ MSL, leaned my mixture back, and started cruising. It was great!

I’d planned a 3-hour leg to Bravo Aviation at KJAS in Jasper, TX, but at about 90 minutes in I suddenly realized that I was just a little light-headed. At first I figured it was the result of eating little for breakfast and skipping lunch to expedite my egress from KSSF. However, after a few minutes, I decided that I might also just be hypoxic. I thought to myself, "Stop being a sissy. You fly the MD-88 in the flight levels all the time. The cabin altitude probably gets up around 8,000’ on an average flight. You should be fine." Not wanting to embarrass myself in front of...myself...I continued.

Can you see where this is going?

After a while, I realized that I was feeling some air hunger. (The feeling that even though you’re breathing normally you’re still short of breath. Your body produces a desire for air that can only be compared to hunger.) At this point I decided I was definitely hypoxic and that I should probably descend.

Great call, right? The problem is that I didn’t descend. I continued cruising as I debated the degree of my impairment, for some reason trying to rationalize my ability to make it far enough to complete my flight with a smooth, elegant, high-speed descent into Japer. Thankfully, after a couple minutes of this I realized that I was on hypoxia symptom #3: reduced mental acuity as evidenced by poor decision making. I rolled my trim wheel forward and started down.

I started to feel better by 7,500’ and felt like I could have leveled-off at 5,500’. Unfortunately, the cloud bases were more tightly packed than the tops and I had to continue all the way down to 3,000’. Yes, it was hot and bumpy and I burned extra fuel, but I was fully conscious and capable of piloting my aircraft. I cringe to think about what might have happened if I’d tried to stick it out in the thin air.

I wish I hadn’t waited so long to descend. I probably went at least 10 minutes from honest recognition of symptoms and knowing that I needed to act, before I actually started down. It scares me that even with 4500+ flight hours and several flights in altitude chambers I still failed to act as soon as I recognized my symptoms. (I now know that impaired judgement belongs on the list that I'll discuss in a moment.)

I was lucky that I had training to prepare me for this situation. I worry that most pilots don't even get the opportunity to discover their personal hypoxia symptoms. This training is interesting and valuable. Here's how it works in the military:

The Air Force requires altitude chamber training for anyone flying above 10,000’ MSL. The training is an all-day event that starts with a few hours of aerospace physiology in a classroom. Then, they take a group of about a dozen aircrew members and lock them in the altitude chamber with an instructor physiologist. Operators pump air out of the chamber, simulating unpressurized operations at high altitude. As a student, you practiceequalizing the pressure in inner ear using the Valsalva maneuver. You also learn that bodily gasses expand as atmospheric pressure decreases. Holding things in only makes it worse later, so the chamber gets pretty smelly.

The most important exercise of the chamber "flight" is a hypoxia demonstration. The operators take the chamber to a simulated altitude of 25,000’ MSL and have you drop your oxygen mask. The instructors have you do visual acuity exercises and puzzles while simultaneously monitoring yourself for any of the hypoxia symptoms mentioned in the classroom that morning. Eventually, all of the students get hypoxic. At that point it’s: mask on, put your oxygen regulator on the emergency setting, and watch how quickly you recover you recover mentally and physiologically. (It is quick!)

Everyone has different hypoxia symptoms (< href="">here’s a list of several possibilities.) I’ve been on several chamber flights and I know my symptoms well. I get dizzy and/or light-headed, and I get a little air hunger. My fingertips and toes start to feel a little numb or fuzzy. Apparently my lips get very blue, though I’ve never had a mirror to confirm that one. I can feel my mental acuity decreasing as I get increasingly hypoxic. I’ve never taken it to the point of full-on euphoria, but I do start edging toward it. In the chamber you’re only supposed to wait until you get 2-3 symptoms before going back on oxygen. Every time I do, the symptoms are gone within seconds.

The moral of my recent experience is: don’t wait! Even if you only have one or two symptoms, get on oxygen or descend!

The next moral is: know your hypoxia symptoms! If I hadn’t gone through the altitude chamber, I might not have even recognized the danger I was in before it was too late.

I’ve heard of civilians getting flights in Air Force altitude chambers. I don’t know how to make that happen, but if you know someone in the AF you should start buying him or her lots of beer. (You should be doing this anyway, but it could get you an invite to visit the altitude chamber someday.) There are also several civilian facilities that provide this training. The FAA has a website with information on enrolling in a course at the Civil Aerospace Medical Institute. They also have an Advisory Circular with great information about hypoxia. A casual search also identified ETC Advanced Pilot Training and Hypoxico, a training device manufacturer that could probably give you a list of facilities using their products. Advances in technology have also made a new type of physiology training available. Instead of using a large, expensive, smelly hypobaric chamber, you can just put on a mask and get hooked up to a machine that controls the concentration of oxygen in your air supply. The machine can simulate the atmosphere at any altitude and you can experience your hypoxia symptoms while sitting in an armchair without all the secondary discomforts that accompany a chamber flight.

Any of the civilian options for this training will cost you money. Don’t let yourself be taken advantage of, but I’d say it’s worth up to a few hundred dollars for a full course. It shouldn’t take more than a day of your time and it’s worth every penny. (If you fly for a living, you might be able to convince your company to pay for the training, or at least give you time off for it. I bet your insurance company will give you a discount on your premiums next year for taking the course too...meaning it could potentially pay for itself.)

Personally, I feel like the altitude chamber is better training than the newer oxygen deprivation chair. I think it’s important to feel and practice dealing with the other side-effects of altitude. It’s also important to feel a little "trapped" and "along for the ride" inside the chamber. A chamber flight will probably cost more, but it’s worth it.

Knowing and recognizing your hypoxia symptoms is one of the most important skills you can have as a pilot. Practicing what to do when you experience them is an exercise worth going through at least once. If you can’t list these skills on your resume yet, go get this training. Taking a course that involves an hour in a cloud of gas isn't glamorous, but it can literally save your life...just like it did for me recently on my trip home.