Thin air

The FAA’s Pilot’s Handbook of Aeronautical Knowledge in Chapter 17 defines hypoxia as “a state of oxygen deficiency in the body, particularly the brain, that impairs mental function and can be life-threatening.

“The first symptoms of hypoxia can include euphoria and a carefree feeling. With increased oxygen starvation, the extremities become less responsive and flying becomes less coordinated.

“Any reduction in mental function while flying can result in life-threatening error,” it concludes.

This is, of course, not a sensation that anyone wants to experience while at the controls of a moving aircraft. Every year, hypoxia—including as a result of carbon monoxide poisoning—plays a role in a handful of general aviation accidents.

But there is a way to experience it without putting yourself at risk. The FAA’s portable reduced oxygen training enclosure (PROTE) is a mobile hypoxia chamber that will make you feel like you’re travelling at more than 25,000 feet above msl, while keeping your actual feet on the ground.

Ezekiel Duran, team lead for the FAA’s Civil Aeromedical Institute Airman Education Program, and his team of experts take the PROTE to events and airshows across the country, allowing pilots, air traffic controllers, and anyone else who’s interested to get a taste of what “useful consciousness” truly is and what it is not.

“It’s very safe because it’s normobaric, not hypobaric, like an altitude chamber,” Duran said. “There’s no pressure change. So, what we’re doing is changing the oxygen concentration in the room that they’re in to equate to 25,000 feet pressure altitude.”

That means the air in the team’s enclosed plastic cube has an effective oxygen percentage of just 8 percent, as opposed to the 21 percent we normally breathe at sea level.Of my five-person cohort in the chamber, only one reached three minutes before he too was making no sense at all, and he didn’t even notice it.

A six-member team carries out these hands-on demonstrations. “We provide the lectures and inside observer duties to make sure that the participants are safe and that they’re able to recover. If, for some reason, they were to pass their time of useful consciousness, we can help them with their oxygen mask and get them back to a good oxygen saturation where they’re cognitively functioning.”

Before the actual demonstration, Duran explains to participants the subjective signs and symptoms of hypoxia that they may experience, including tingling, air hunger, hot or cold flashes, or tunnel vision. Other symptoms include headache, impaired judgment, euphoria, lightheadedness, and increased reaction time.

As hypoxia worsens, the Pilot’s Handbook of Aeronautical Knowledge tells us, our field of vision begins to narrow, and even basic tasks become impossible. Even with all these symptoms, “the effects of hypoxia can cause a pilot to have a false sense of security and be deceived into believing everything is normal.”

That’s exactly what it felt like inside the chamber. When I walked in, my finger pulse oximeter showed an oxygen concentration of 99 percent and my pulse was 75 beats per minute. Within a minute, my oxygen concentration had dropped to 69 percent, and my pulse spiked to about 112. My ears felt warm, as if being blasted by a heater from behind, and I somehow knew I was struggling to breathe enough oxygen to keep my brain working normally.

I tried to complete some tasks on a worksheet I had been given—simple math problems, and a word search puzzle. Even though I was reading and understanding the words and numbers on the paper before me, I was having a bit of trouble with “152 + 608 = ?”.

Another minute later, my oxygen was down to 67 percent. I still felt like I needed more oxygen but otherwise thought I was relatively rational and lucid. When one of the team members asked how I was doing, I slowly lifted my head to look at him and gave the thumbs-up sign. While I didn’t experience true euphoria, I did have the sense that I was kind of invincible.

There must have been something about my glazed eyes, prompting him to immediately say, “Put on your oxygen mask.” Just two and a half minutes had passed.

Of my five-person cohort in the chamber, only one reached three minutes before he too was making no sense at all, and he didn’t even notice it.

After a few breaths from an oxygen mask, everything was all right again.

“In this demonstration, at over 25,000 feet, the average time of useful consciousness is three to five minutes, but everyone is physiologically different,” Duran said. And indeed, each of us had experienced different symptoms.

“It’s really good to key into and remember your specific symptoms.”

And often in hypoxia situations, it’s the air traffic controllers who notice first that something may be amiss in the cockpit.

“Communication is a big red flag,” he said. “If a pilot [flying] at 10,000 feet or higher is showing mental confusion or suddenly has a different speech pattern or maybe some ambiguity, that controller can suspect signs of hypoxia.”

It’s rare that a pilot will fly at an altitude that requires supplemental oxygen without actually having oxygen on board, Duran added. Yet hypoxia happens to those folks, too. The top five reasons this occurs are: 1. a kink in the hose delivering the oxygen, 2. the hose is not attached properly, 3. the tank runs dry, 4. they didn’t turn on the system, or 5. the nasal cannula freezes up or is blocked.

Duran said his team is on the road for about 11 weeks every year, doing demonstrations at major airshows like EAA AirVenture and Sun ’n Fun, or for smaller groups. They preach that the most effective way to prevent a hypoxia incident is to experience it first-hand in a safe and controlled environment.

“Awareness is key, right? So obviously, see something, say something. And in this context, we also say, ‘feel something, say something.’”

“If you as a pilot were to start to feel not normal, or have some type of symptom that is different from what you normally feel when you are flying, then take a look at, hey, what altitude am I at?”

Then take appropriate measures to try to stop those symptoms before they become critical.

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