SAFA Skysailor Magazine

53 SPRING 2025 | September-October-November SKY SAILOR a minute later the finger unit shows 96%. A fair bit of variation. What sort of numbers should we be looking for? Well at the extreme end of things, if you see 60% or somewhere close to it, you’re in BIG trouble, as in your death is imminent . Normally we would expect to see 96-99%. Up to 10,000ft AMSL (3030m) we would expect to see 90-97%. This stage of hypoxia is referred to as the Indifferent stage. The next stage, Compensatory , runs from 10,000 to 15,000ft AMSL (3030-4500m); we would expect 80-90% saturation. Next comes the Disturbance stage, at 15,000 to 20,000ft AMSL (4500-6000m) and 70-80% saturation is expected. Finally, is the Critical stage: 20,000 to 23,000ft AMSL (6000-7000m) with saturation values of 60-70%. This is really dangerous territory – the next stop is death. Recommendations? I’d say the gold standard is the fingertip-type device, but it is impractical for use in flight. For smart- watches it comes down to how you rig your cockpit and clothing: can you access a fiddly small screen on the watch and hold still with one hand off the controls, or access your smartphone screen? And the more fundamental question should guide you, are you at risk either through physi- ology, or by the altitude you are currently flying at? However you cut it, something is better than nothing if you spend a lot of time inhabiting higher altitudes. References: 1) www.britannica.com/science/hypoxia 2) www.avmed.in/2011/03/ flying-into-thin-air-understanding-hypoxia/ 3) www.flightsafetyaustralia.com/2014/08/ do-not-go-gentle-the-harsh-facts-of-hypoxia/ 4) www.faa.gov/pilots/training/ airman_education/topics_of_interest/hypoxia/ 5) www.youtube.com/watch?v=6yQFcXpFwX8 Figure 4: Finger SPO2 measurement