Pilot Brad’s Flying Blog

A few weeks ago I had the pleasure of attending an FAA Aerospace Physiology class at Beale AFB outside Marysville, CA.   While the words Aerospace Physiology might sound a bit intimidating, the FAA simply says that Aerospace Physiology deals with the physical and mental effects on flight aircrew personnel and passengers.  That being said, the primary focus of this class is to teach you about the affects altitude, and decreased oxygen, have on the human body.  Anyone who holds a current FAA Medical Certificate may take the class at about a dozen or so locations around the country, at a cost of only $50.   If you are interested, you can learn more about the training and other on the FAA’s Airman Education web site.

This class is required component of your training and certification if you are going to be flying pressurized aircraft, and the conclusion of the training you are given FAA Form 3150-1, which is often referred to as an “Altitude Card”.  So why did I take the class if all I am flying is non-pressurized C172s?  Why not!  Seriously, I am always open to any form of training on new and old topics alike, and since reduced oxygen can have an effect on the body at almost any altitude I think the training is worthwhile for most any GA pilot. 

The topics covered in this class were; Physics of the Atmosphere, Respiration and Circulation, Stress, Vision, Noise, Physical Fitness, Hypoxia, Hyperventilation, Trapped Gas, Decompression Sickness, Pressure Equalization Difficulties, General Aviation Oxygen Equipment, and an Altitude Chamber Flight.  Yup, you read that right; the highlight of the class is a ride in an altitude chamber to demonstrate the effects of altitude on the body (your body).  I’ll go more into that later, so you’ll just have to read on.

Beale AFBis home of the 9th Reconnaissance Wing and 12th Reconnaissance Squadron  which means that it is a functioning U-2 and UAV base respectively.  This became very apparent as I approached the flight line and found about a half dozen U-2s and RQ-4 Global Hawks, along with some other Air Force hardware parked on the ramp.   Cool, very cool!

After arriving at the appropriate building, my classmates and I were escorted into the classroom by a member of the 9th Physiology Support Squadron, where we found a U-2 pilots flight/pressure suit and related flight gear on display.  The squadron is responsible for providing support and maintenance for the U-2 pilot’s pressure suits as well as operating the altitude chamber and conducting physiology training for military staff and civilians.

We were joined by our Air Force instructor for the day who asked us to go around the room and introduce ourselves.  Since I was sitting in the front row she asked me to go first, telling the group my name, where I was from, and my flight experience.  It went something like… “My name is Brad, I am private pilot from the Bay Area, I currently working on my instrument rating, and I am building an RV-7 in my garage.” 

I ‘m glad I went first because I don’t know how I would have followed some of the people in the class.  The next guy turned out to be a senior test pilot for the FAA in their experimental aircraft division, and he had just completed his B747 and B777 re-currency training.  The three guys after him were all ATPs, one of which had 42,000 hours.  After the ATPs was the Chief Flight Engineer (test pilot) for a well known military aircraft manufacturer, who had spent plenty of time at Edwards AFB.  Needless to say, there was some serious pilot experience in the room (present company not included).

After the introductions we dove right into the lesson, learning all about the atmosphere, its composition, and the related physical gas laws.  The topics then changed to the human body and how changes in the atmosphere (pressure) have an affect on it through the various gas laws.  For example, Boyle’s law tells us that “A volume of a gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant.”  This means that as you ascent, gases trapped in your body increase in volume.  Areas such as the middle ear, sinuses, teeth, gastro-intestinal tract and the lungs can all be affected, with the best case being that you’ll stink up the cockpit, with worst case scenario being severe pain or even incapacitation. 

While it is important to understand the concepts of trapped gases and how they can impact the body, the most important subject covered during the training was hypoxia.  The altitude chamber flight is a hypoxia demonstration, so you could say that hypoxia was the main reason we were all there that day.  As pilots we all know, or should know, that hypoxia is defined as a state of oxygen deficiency in the blood, tissues and cells sufficient to cause impairment of bodily functions, but did you know there are four types of hypoxia?  There’s hyopxic hypoxia, hypemic hypoxia, stagnant hypoxia and histotoxix hypoxia.  In the interest of time I won’t go into them here, but you may read about them on your own if you like.

Our instructor spent a fair amount of time talking about the symptoms of hypoxia.  Since all pilots experience some reduction in available oxygen during flight, even at low altitudes, we learned how critical it is for us to understand and recognize the symptoms.  The symptoms are air hunger, fatigue, nausea, headache, dizziness, hot and cold flashes, tingling, visual impairment, and perhaps the most dangerous of them all, euphoria.  When the brain starts to feel the effects of hypoxia, the higher reasoning portion of the brain is first affected, and this is why it is so critical to recognize and respond to hypoxia as quickly as possible.  Otherwise you could end up in a situation where you are convinced that everything is just fine, when in reality you are bordering on unconsciousness.

As an example of how quickly reasoning and judgement can become impaired, they showed us a video, which as luck would have it I found on YouTube.  The story we were told was that this Air Force pilot was at 35,000-ft in the altitude chamber, which typically yields a time of useful consciousness between 30-60 seconds.  He starts off fine, but you will see just how quickly the affects of hypoxia take their toll on him.  It’s both very funny and very serious. 

After a morning full of learning we were all hungry so they turned us loose for lunch.  Well, as loose as a civilian can get on an active military base.  They had just opened a new cafe a few hundred yards from the physiology building so we all took the short walk for lunch.  As we walked past several hangars, we could see several more U-2s and RQ-4 Global Hawks parked or in various stages of preparation for flight.

After a pleasant lunch, we were sitting at our tables conversing when the sound of aircraft overhead rumbled the cafe.  A bunch of us walked outside to the cafe’s deck to see something you don’t see every day, two U-2s in the pattern doing touch and goes.  After a bit, one of them then departed and was out of sight in what seemed like only seconds.  I probably could have watched them for hours, but it was time to get back to class, and to prepare for our chamber flight.

We arrived back at the physiology building, and our flight engineer/test pilot classmate ran into a test pilot friend of his in the lobby.  This kid was probably in his mid-20s and was getting ready to graduate from test pilot school in a week or two.  According to the flight engineer in the class, he was going to get 1 hour in the U-2, in which he must answer the question, “If you only get 1 hour in the airplane, what would you do to evaluate it?”  I asked our classmate why he is only give the hour, and he told me it is to see how well the student evaluates the aircraft in a short amount of time.  In addition, it simulates a situation such as when a pilot defects from another country in one of their aircraft, and we only have 1 hour to evaluate the aircraft before it is given back to that countries government.  OK, sounds good to me. 

Back into the classroom we went as we still had much to learn.  In the afternoon session, our instructors covered the topics of pressurization, decompression, and oxygen equipment.  They stressed just how important it is for us as pilots to understand our equipment and the proper way to use it.  In other words, be prepared, learn about your equipment in advance as the time to figure it out is not when you are in the air, or in an emergency situation. 

With the classroom lesson for the day complete, it was time to get our helmets and masks in preparation for the altitude chamber flight.  After our fitting we were escorted into the chamber and told to sit in our assigned seats, where we were connected to 100% oxygen.  After everyone was settled and connected, our instructors made sure that each of us was familiar with the equipment that we would use during the flight.  They then closed the door for a quick trip up to 5,000-ft (at 3,000 fpm!) for an ear and sinus check, which is performed to ensure each student is comfortable with equipment and is not having any problem equalizing.

With the ear and sinus check successfully completed, they descended the chamber back to ground level and opened the door, and we then sat in the chamber for pre-breathing 100% O2 for 30 minutes while we waited for the oxygen to purge the nitrogen from our blood system.  If this wasn’t done, there is a good chance that during ascent the nitrogen would bubble out of your blood and give you the bends (or other problems).  This is the same reason why scuba divers have to take their time when coming up from the deep.

Once our Air Force instructors were satisfied that we had adequately pre-breathed, the door was shut once again and the ride began.  The chamber began ascending from ground level pressure to 8,000-ft a 3,000-fpm, and then a rapid decompression from 8,000-ft to 18,000-ft in only 8-10 seconds.  I could feel the change in pressure as my inner ears struggled a bit to keep up with the ascent rate.  The coolest part about the rapid decompression was the cloud or fog that quickly formed in the chamber, which I’ve never had happen in a C172 on climb-out, but could happen if you had a rapid decompression of a pressurized aircraft.

After a brief pause at 18,000-ft the ascent continues at more reasonable 3,000-fpm rate to a peak of 25,000-ft.  Our instructors verified everyone’s well being, and we were told to remove our masks and see how long it took for us to recognize the symptoms of hypoxia.  Within 30 seconds I could tell something was different.   It’s a bit hard to describe; I could feel that my lungs were having to work harder to get the needed oxygen, but overall I felt OK, and after a few minutes I remember thinking it wasn’t so bad (danger sign). 

We all had communication systems in our helmets and you could hear our instructors talking to various students in the chamber.  They seemed to be picking on one guy and when I looked over at him it was obvious why; He was somewhat incoherent and on the verge of unconsciousness.  It was scary but enlightening that after only a few minutes someone could get to that level. 

My attention then shifted back onto myself, and I noticed that my reactions to everything seemed to be slowing.  While I could understand everything that was going on around me, I felt as if nothing was really wrong (more signs of danger).  I remember thinking to myself, “This really isn’t that bad, I wonder why that guy almost passed out?”  I stuck it out for a few minutes, but our instructors didn’t want us to go too far so they encouraged us to go on O2 as soon as we could detect two symptoms.  I had nothing to prove, and I could definitely feel a slowness to my reactions, so I decided to take the appropriate actions and don the mask and gang-load the regulator (100% O2 in Emergency mode).

It only took a matter of seconds before I realized just how affected I had become.  The rush or oxygen now flowing to my brain felt like going from slightly drunk to sober in just a matter of seconds.  I was shocked at how much more aware and sharp I was, and just how bad I had become without completely acknowledging it.  It was clear that I had been suffering from euphoria, which as I said earlier is perhaps the most dangerous of all symptoms. 

I knew that I was in an altitude chamber and what to expect, but what if I were flying along at 14,000-ft and hypoxia started to set in.  The danger is that I might be lulled into thinking that everything is just fine, all the while I am getting progressively worse.  Again, this is why it is so critical to quickly recognize and react to the first signs of hypoxia.

Our time at 25,000-ft was short, but the ride wasn’t over just yet.  We descended back down to 18,000-ft where the lights were turned off and we were told once again to remove our masks.  The purpose of this was to demonstrate how our night vision would be effected by being slightly hypoxic.   We were each given color wheels, and asked to observe changes to the colors as time passed.  After a few minutes I could see the colors dim a bit, but I could still clearly distinguish them.   Towards the end of the simulation we were told to go back on oxygen while we continued to look at the color wheel and observe and changes.  People reported very different results, but for me certain colors seemed to momentarily glow as higher amounts of oxygen clearly reached my eyes and brain.

The ride back down to ground level was much more gradual as this is where people frequently have issues with their inner ears.  Pinching my nose through the mask and performing a few valsalvas seemed to do the trick for me, and by the looks of it for everyone else as well.

Overall it was very cool day, and I learned a tremendous amount.  It was well worth the time and expense, as it was really enlightening to actually feel the alluring effects of hypoxia first hand, and I now feel much better equipped to recognize the symptoms.  While I probably won’t have an immediate need for the knowledge I gained today, it will make me think twice about how I prepare for a high altitude flight, such as when crossing the Sierra Nevada mountains.

Last but certainly not least, I would like to offer my sincere thanks to the men and women of the 9th Physiology Support Squadron for their professionalism and service to our country!