October 2004
How high can you fly? That’s a question that’s bothered me for quite a while now. The San Francisco sectional I use regularly has some green in the middle, where the California central valley is—but there’s brown on the chart, both for the coast range mountains to the west (elevation around 3000-4000′) and a lot more brown to the east, where the Sierras rise to elevations of 10,000-14,000′.
Going north or south you’ll run into mountains as well, so if you fly any distance at all out here you’re going to run into altitude issues. Which raises a question: How high can you fly?
The book answer, from FAR 91.211 is: up to 12,500 feet unless you have supplemental oxygen. From 12,500 to 14,000 feet the pilot in command is required to use supplemental oxygen if you’ll be at that altitude for more than 30 minutes.
Above 14,000 feet the required minimum flight crew (for most of us, the pilot in command) is required to use it, above 15,000 feet everyone in the airplane must use it… and then there requirements for pressurized aircraft, which I won’t get into here.
In practice, though, you may need supplemental oxygen at lower altitudes. I found this out a few years ago, on the way home from a trip to Mexico. My IFR route ran through the Banning Pass, east of Los Angeles, with an MEA of 10,000 feet.
Shortly after reaching that altitude, I began to feel ill. I asked for and got a lower altitude temporarily, but quickly got worse and actually declared an emergency. I was given immediate clearance to land at Ontario International (emergency equipment lined the runway) and was taken to a local clinic.
The diagnosis was gastroenteritis complicated by altitude. In plain English, I got a bad case of Montezuma’s revenge.
The part of this that’s significant (aside from watching what you eat and drink south of the border) is my symptoms—which were classic for altitude sickness. First, I got a headache—then nausea. Then I started to lose my peripheral vision and was at risk of passing out. That’s a heck of a feeling to get when flying an airplane without an autopilot!
My wife took the controls (and not long after, started her flying lessons—she’s now a licensed pilot too) and by our next trip, I owned a portable oxygen bottle. I’m on oxygen any time I’m at or above 10,000 feet.
Since doing that, I’ve never had any symptoms of altitude sickness in the air. I’ve also found myself less fatigued at the end of long legs.
Curiously, it turns out I’m not the only pilot to enforce a rigid “10,000 feet or higher” rule—that’s the standard used by the US Air Force. I learned that last month on an all-too-brief visit to “Reccetown USA,” Beale Air Force Base.
I was there to attend a one-day Aerospace Physiology class, which included about an hour in an altitude chamber capable of operating at pressure altitudes up to about 75,000 feet (we only went to 25,000). I was one of a dozen private pilots attending training courtesy of the FAA’s Aviation Physiology Training program—on which I’ll have more to say later.
I can’t tell you anything about flying into Beale—that would have required special arrangement with the Base Commander (who I doubt would have authorized it). Instead, three of us from Modesto drove in (about two hours).
Some of the others, coming from the Los Angeles area (400 miles south) flew into Marysville Airport nearby. The FAA discourages this, in case you have an ear block or some other bad reaction in the chamber. However you get there, you’ll probably have to spend the night before training—you’re expected at 07:15 local time.
On the way in, we had to pass through Beale’s main gate, and have our IDs checked by security police, who issued temporary passes. Then we drove to the home of the 9th Physiologic Support Squadron, passing the “Reccetown USA” sign on our way—that’s a take off on “Fightertown USA,” Miramar Naval Air Station (home of “Top Gun”).
Beale is home to the U-2 Reconnaissance airplane, which flies at altitudes above 70,000 feet. At those altitudes, not only is oxygen required, it has to be provided under pressure to the entire body, requiring a full-pressure “Space Suit”. The 9th is the central depot for U-2 suits for both the Air Force and NASA (which uses some U-2’s for research purposes).
Our instructor for most of the day was Capt. Brian Musselman, USAF. He’s a 650 hour private pilot along with his Air Force duties. Attendees had a wide range of experience—we had several CFIs. Oddly, I seemed to have the most flight experience, with about 1,000 hours.
He told us that we were getting a very abbreviated version of the course given to U-2 pilots, which lasts nine days. The lectures pretty much repeated—and expanded on—the short bit on flight physiology that we all get as part of our private pilot training.
It included composition of the atmosphere, examples of what can happen to pilots who become anoxic without realizing it (I was particularly impressed by a case where two GA pilots had to make an emergency landing after running out of fuel… less than five miles from their destination airport on a CAVU day as a result of anoxia). We were shown video of an Air Force pilot in the altitude chamber who was unable to correctly identify playing cards after only a few seconds at 25,000′ pressure altitude.
The lectures weren’t limited to altitude effects—we were also given training on fatigue, spatial disorientation (including an opportunity to experience it, in a special rotating chair) and effects of alcohol and drugs.
After a nice lunch in one of the base cafeterias (we were advised to avoid beans and carbonated drinks) we were fitted for oxygen masks and helmets—required because military masks attach to the helmet rather than being worn directly on the face. For me, this was the most uncomfortable part of the whole experience. My beard probably interfered with getting the mask to seal, and I wound up with one that was really too tight for comfort—but it worked for the one hour I needed to wear it.
Then to the chamber: It’s a steel cylinder with jump seats along the walls for a dozen students. Each seat has a military oxygen regulator, into which the supply tubes for our masks were attached, plus audio plugs for the microphones and headsets built into the helmets. Three or four instructors were in the chamber with us, while more looked in from outside through windows.
Once everyone was plugged in, masks were donned and checked, and the door was dogged down. Then pumps started up, and took us to 8,000 feet pressure altitude to verify that everything worked. Everyone checked out OK, and they took us back to surface pressure (at an apparent rate of about 2,000 FPM) to make sure everyone could clear their ears—anyone unable to do so would have been dropped off at this point.
We all put our masks on and “pre-breathed” pure oxygen for 30 minutes. That minimizes the risk of developing “the bends” (having bubbles of nitrogen form in the bloodstream) which can happen on rapid decompression—if you’ve ever wondered why the FAA doesn’t want you to fly for 24 hours after scuba diving, that’s the reason.
With oxygen pre-breathing, and any nitrogen having (hopefully) been removed from our bodies, the pumps started up again, and this time we went to 25,000 feet pressure altitude—and we got there fast. The effective rate of climb was something like 3,000 to 4,000 feet. It also got noticeably cold.
Once we “leveled off” the instructors checked to make sure that everyone was OK… and then told us to take our masks off. We each had a clipboard with simple questions and math problems. I took my mask off, got the clipboard and started at the top. The first few questions were easy, but the math problems started giving me a headache.
It was frustrating, looking at two numbers and knowing there was a simple way to multiply them, if only I could remember what it was… Then I started to get a familiar feeling of nausea. I didn’t wait for anything else, and got my mask back on.
“Good recovery” came the word from the instructors. I looked around to find that I was the first one to give up—and that only about 30 seconds had gone by.
Over the next minute or two, most of the others gave up too—but we had a couple of holdouts who went the full five minutes before being told to put their masks back on. This backed up what the lectures told us: Some people have a much higher tolerance than others. They remained conscious and alert for the whole time, though one reported a mild headache.
By the end of the five minutes, both had noticeably bluish lips and fingernails—which gained normal color in just a few seconds once they put their masks back on. Once we had all recovered, they took us down to 18,000 feet—at which point one trainee, a former Navy submariner—had trouble getting his left ear to clear.
The descent stopped as soon as the instructors noticed his difficulty, and they worked with him until he could clear. Then our descent continued. At 18,000 feet, the lights were dimmed and we were all handed plastic-covered sheets with a sectional chart on one side and a color wheel on the other. Then we were told to remove our masks.
This time, I was able to go the whole five minutes, with no gross symptoms beyond a slight (but noticeable) headache. I had no trouble identifying the colors on the chart, but my visual acuity started to go, and by the end of the 5 minutes I could not read the print on the sectional. Most of the other trainees lost color vision.
It was positively amazing how quickly things improved once I put the mask back on—it was as if the chart was slightly out of focus and “popped” into perfect focus on about my second or third breath of oxygen! Our masks were checked again and descent started—with special attention to the ex-submariner with ear trouble.
In just a few minutes, we stepped out at sea level.
There was a debriefing for about half an hour (focusing on who to call if any delayed symptoms of bends or other effects showed up later) and we hopped back into the van for the two-hour drive home.
One more lesson from all this: I was completely beat the next day. A one-hour “flight” involving just two climbs and three descents may not sound like much, but the five-minute stops at 25,000 and 18,000 feet took a lot out of me. I wouldn’t want to come back and do it again two days in a row!
The FAA works with the U.S. Air Force and Army to provide physiologic training at various facilities around the country. It costs $50 per person (plus whatever your travel and hotel costs). You can do the training free at FAA headquarters in Oklahoma City. For details, browse https://www.cami.jccbi.gov/AAM-400A/Brochures/PT_Course2.htm or call (405) 954-4837. –JDR
John D. Ruley is an instrument-rated private pilot, and a freelance writer specializing in science and technology. He’s also a volunteer pilot for LIGA International (www.ligainternational.org), and past president of the Modesto Airport Pilot’s Association. You can write to John at jruley@ainet.com.
