It's toxic to be hypoxic
Student pilots dutifully learn the regulation that requires the use of supplemental oxygen, FAR Part 91.211, and proudly display their rote memorization for the DPE on their check ride.
Especially for new pilots flying in the East Coast, the oxygen requirements seem to be among the least relevant of all regulations. Flying at 12,500 feet seems the realm of higher performance aircraft and higher time pilots. So, what gets filed away in our flying database is, “Since I am not flying above 12,500 feet, oxygen is not required.”
The reality of our physiology is much different. Research going back to the 1980s shows that at altitudes as low as 8,000 feet our Blood-Oxygen Concentration (SpO2) can reach a critical level of 90 percent. At this point, our bodies begin to experience the effects of hypoxia. Remember the phrase “O2 Over 8 Feels Great.”
Cruising at 8,000 feet is a typical cross-country altitude for a light general aviation aircraft–you fly above most of the airspace and traffic, true airspeed increases, and you are typically above the turbulence.
However, being even mildly hypoxic at or above 8,000 feet for hours can lead to hypoxic symptoms of fatigue, headaches, and slow decision making–especially for us flatlanders on the East Coast. Indeed, NASA ASRS reports include many reports from pilots flying below altitudes at which oxygen is required experiencing mild hypoxia and missing altitude assignments, headings, and having other difficulties in flight.
With the appearance of low-cost and integrated pulse oximeters, pilots can monitor their blood oxygen levels and even set alarms. Smart watches and other devices allow us all to know our blood oxygen level and track it as we climb so we know at what altitudes we are crossing below that critical 90 percent mark. Our tolerance to altitude will vary with factors such as fatigue, hydration, stress, and other factors, so monitoring it on every flight is critical.
Pilot wellness is not about being legal–it's about being safe and operating at our peak performance. Think of supplemental oxygen as a turbocharger for your brain. Just like a turbocharger maintains sea level engine power at altitude, supplemental oxygen maintains brain power at altitude too.
So file that regulation away in your brain until your next check-ride, and think instead, “It's toxic to be hypoxic.” With that in mind, use supplemental oxygen at or above 8,000 feet by day, and above 5,000 feet at night.
