In the last decade as inexpensive, accurate pulse oximeters came on the market and pilots put them into widespread use, they provided firsthand evidence to confirm what medical professionals had been saying for more than 50 years: The Federal Aviation Regulation concerning supplementary oxygen use in flight—91.211—is hopelessly inadequate to protect pilots and passengers from the dangers of hypoxia. A pilot who is in full compliance with 91.211 is often oxygen-deprived to the extent that safe operation of the aircraft is in question even if the pilot has to deal with nothing more than routine flight operations.
