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FAA recommends general aviation aircraft to stay below 5,000 ft at night time. I thought the reason is that oxygen usage with our eye's rods since the rods uses much oxygen and rods can get hypoxia which makes tunnel vision and eventually not able to see outside. But one of my friends claimed the reason why we are supposed to fly at a lower altitude to prevent from hypoxia is that at night there is higher pressure near the ground which makes fewer air molecules at high altitude at night than daytime.
- Is this true that we get hypoxia more easily at night time because of pressure and that's the reason why FAA recommends us to fly below 5000ft?
- If the question number 1 is not true (from my understanding), is rods problem the only reason why FAA recommeds us to fly below 5000ft at night time?