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Up in the Air

The Normalcy of Deviance: Why Pilots Break This Rule

Erika Armstrong - Thursday, December 28, 2017

As we leveled off at FL510, I couldn’t wipe the smile off my face. Even though this altitude would make an SR-71 pilot roll their eyes, it still felt like we were on the edge of the universe. You could see the transition of our atmosphere to the darkness of space, it was eerily quiet, and the curve of the earth reminded me I was less than a speck in the cosmos.


The cabin altitude was still holding nicely at 6,800 feet and since I live in Colorado at 8,700 feet (MSL), I had more pressure in this cabin at FL510 than at home. Even though we were highly experienced pilots, honoring a positive safety culture while sitting in a $23 million aircraft, we were blatantly breaking the rules. Neither of us had our oxygen masks on, but we did set them in our laps as a compromise. It was a reminder to keep our attention on pressurization, but now our “quick donning” design was altered with them in our laps. It’s not a cavalier attitude, it is a calculated risk with the sum of odds close to zero.


Even though pilots are rebels at heart, pilots like rules. The rules give us comfort. We know there is a reason for them so we don’t question them. It’s one less thing we must do while trying to make a thousand decisions an hour. We peer pressure each other and create a safety culture which prides us into following all the rules, not just some of them. We accept that, we honor that, we promote that. So, when there are rules which are out of date and don’t keep up with technology, not following one rule begins the slide towards the normalcy of deviation. If we question one rule and don’t follow it, there is a shift of perception that maybe other rules should be questioned…and not followed. This creates the dreaded: noncompliant pilot.


The Code of Federal Regulation Part 91.211 says in general that one pilot needs to be wearing an oxygen mask always above FL410 and at FL350 and above if the other pilot leaves the cockpit. Part 135.89 (let’s just focus on high performance, pressurized aircraft with cabin pressure below 10,000 ft MSL and pressure-demand oxygen systems) reminds us that at least one pilot at the controls will wear an oxygen mask at FL 250 and above if the other pilot leaves the cockpit and at all times above FL 350 (your Op Specs might be even more restrictive). Since most business jets are consistently operating much higher than that, there should be a lot more nasal sounding conversation (the Darth Vader voice via the mask) on the frequency, but there isn’t.


For the righteous pilots who always have their masks on as required, you can stop reading. We bow down to your professionalism and honor your self-discipline. For those of you smirking, let’s talk. Technology has improved immensely since this rule was put in place and airplanes are flying even higher. We know about the Payne Stewart accident and everything there is to know about hypoxia. I’ve been in an altitude chamber and listened to my normally non-humorous co-captain give the answer to 1+1 as “one thousand, one hundred onety-one” as he laughed his way through hypoxia. It is deadly, and we know it. But the steel horses we fly are now so self-aware and self-sufficient, they tell pilots when the cabin pressure is too high. They indicate trends, sound alarms, bells, warnings and automatic pax mask release. Automatic Emergency Descent Systems in some aircraft will automatically descend to MSA if pilots fail to respond to a cautionary alert. This system will even sidestep off-track to avoid traffic conflict.

For the explosive decompressions at FL510 (or even rapid, depending on the situation), we know we’re pretty much doomed and the mask won’t be much help as our internal pressure exceeds what is humanly possible to stay alive. The instant pain will be overwhelming and hypoxia will be instant, even with a pressure demand mask. If we have an explosive decompression up there, something is seriously, structurally wrong and an O2 mask won’t fix that. A gradual decompression is just as deadly (and more probable) because you don’t sense it before hypoxia settles in…but the airplane will.

Pressurization incidents still happen all the time. Sometimes pilot induced (forgot to turn on bleed air, system set to manual, etc.), but the reliability of modern business aircraft pressurization systems is extraordinary. But, like I said, incidents happen all the time so should we wear our masks like the rule states? Here's the first dilemma, they’re not meant to be worn all the time. They’re designed for an emergency, which is temporary. The requirement to use these masks constantly during normal operations goes against how the system and aircraft were designed and how an emergency oxygen system was meant to be used.


When pilots put on the mask, their environment changes. They are instantly trapped and confined, communication takes effort, and CRM is disconnected. It’s hard to move, the pressure on your head and face is fatiguing, and consistently sucking on higher levels of oxygen is harmful, if not toxic. We normally breathe air that is 21% oxygen at sea level. That ratio is the same at FL510, but because of the reduced pressure (molecules farther apart), we can’t get that ratio into our lungs. But, that’s outside. As I mentioned, the cabin altitude/pressure at FL510 is still 6,800 feet in this particular aircraft. Our bodies are getting what we need, so now we add on supplemental oxygen and start breathing it, for hours at a time…over a lifetime.

Toss in some germs next. When I was flying at the airlines (we have different rules which I won’t get into, but same concept as Part 135), we would always check our oxygen masks before departure. We’d put them on, test the microphone (“Luke, I am your father…”) and put them back. At night, we’d often take a “sip” from our masks as we started our descent which acted like a shot of caffeine. We all did…which meant we all were exposed to each other’s germs too. We had to provide the wipes, but breathing warm, moist air into these masks weren’t going to get clean by a pilot doing a quick swipe, which is all we did. And, we used alcohol wipes, which probably isn’t good to be mixed with O2 and degrades the materials of the mask.

For the employees of the FAA and NTSB reading this, they have already smacked their foreheads and have mumbled something about pilots always complaining. It’s just an oxygen mask, just put it on! The point to all this is that the reality is: pilots don’t put on the masks, but they also don’t like breaking the rules. We don’t want to be deviants and those righteous pilots from the previous paragraph will look down at us. There should be strict oxygen and cabin pressure rules, the same for all ops (Part 91, 135, 121 etc. should all be the same), but they should be based on equipment capabilities, cabin altitude and service ceilings - and more focused training (and practice) for using quick donning masks. Maybe simply adding a requirement to check cabin pressure after a frequency change or every 15 minutes above FL250 would suffice.

This is not pilots asking for any rules to be relaxed. It would be a genuine increase in safety to use the oxygen systems as they were meant to be used, to train on how they were meant to be used, and to train on the vigilance of monitoring the pressurization system. What the FAA is asking of pilots now is to go against the manufacturer’s intended use of an aircraft system. So, who is actually breaking the rules…

 From the front desk of an FBO, to the captain’s seat of a commercial airliner, Erika Armstrong has experienced everything aviation has to offer. She is an aviation professor at MSU Denver, Director of Instructional Design at Advanced Aircrew Academy and author of A CHICK IN THE COCKPIT. This article is meant to just get the conversation started so if you want to add your side, Erika can be reached at

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