On Thin Air
By Dr. Susan Northrup, FAA Federal Air Surgeon
Hypoxia (decreased oxygen reaching tissues) is an inherent risk for many in aviation, but there is training as well as regulatory requirements designed to mitigate it.
Pilots who operate pressurized aircraft capable of flight above FL250 are subject to the requirements of 14 CFR section 61.31(g). This regulation ensures that, with certain exceptions, pilots are trained to recognize hypoxia, decompression sickness, and the duration of consciousness at different altitudes. While the training is a one-time requirement, we encourage pilots to regularly reacquaint themselves with these subjects even if not mandated by their employer or insurance company. Note that the U.S. military requires that many of its pilots receive a full day of training, including a chamber ride, every five years in addition to initial training. We encourage pilots to consider at least some of the training covered under section 61.31(g), even if you’re not subject to those requirements. Hypoxia can occur at altitudes well below FL250 and some pilots routinely fly unpressurized aircraft above FL250.
We also recommend hypoxia training for air traffic controllers. Many pilots have been helped by a controller who recognized that a pilot had hypoxia symptoms.
Some pilots believe that living at a higher altitude offers significant protection from hypoxia. This is partially true. Without question, someone who lives at 9,000 feet will handle an excursion to 12,000 feet better than someone who lives at sea level. However, this benefit rapidly decreases and is subject to individual variability.
So what exactly are the applicable regulations? For the general aviation pilot, 14 CFR section 91.211 applies. While most of us are familiar with the need for oxygen above a cabin pressure altitude of 12,500 feet mean sea level (MSL) for flights over 30 minutes and all flights above 14,000 feet MSL, there are additional rules for pressurized aircraft. For commercial operations, 14 CFR sections 121.327, 121.329, 121.331, 121.333, and 135.89 apply. Note that 14 CFR section 121.333(c)(3) was changed, effective May 23, 2020, to comply with section 579 of the 2018 FAA Reauthorization Act.
Many FAA handbooks discuss hypoxia. In addition, the FAA offers a number of other hypoxia training tools, including an Advisory Circular (AC) 61–107B CHG 1, Aircraft Operations at Altitudes Above 25,000 Feet Mean Sea Level or Mach Numbers Greater than .75; videos; Aeromedical Safety Brochures; and an in-person, one-day course in Oklahoma City. The latter includes training in either the altitude chamber or the PROTE (portable reduced oxygen training enclosure). Both expose the participant to an oxygen level equivalent to FL250. In the altitude chamber, the atmospheric pressure is reduced, demonstrating attendant effects on the ears, sinuses, etc. The pilot experiences both controlled (normal) ascent and a rapid decompression, but it can expose the participant to a small risk of decompression sickness. Contact the FAA physiology section at (405) 954–4837 for further details.
A newer, alternative method of demonstrating hypoxia is to have the participant breath air that has a lower percentage of oxygen. A quick internet search will show a number of commercial providers who offer this training. The FAA version, PROTE, is offered both in Oklahoma City as well as at events like AirVenture and Sun ‘n Fun. Since our demand typically exceeds our availability, we are now exploring the possibility of purchasing an additional PROTE system. In the meantime, fly safe and use oxygen before you think you might need it.
Dr. Susan Northrup received a bachelor’s degree in chemistry and a medical degree from The Ohio State University, as well as a master’s degree in public health from the University of Texas. She is double board certified by the American Board of Preventive Medicine in Aerospace Medicine and Occupational Medicine. She is a retired U.S. Air Force colonel and a former regional medical director for Delta Air Lines. She is also an active, private pilot.