Originally Posted by
BelArgUSA
The 10,000 feet is an arbitrary figure... In the FAA, CAA and JAR books.
Maybe other books.
I doubt it means anything to people who live all their life at 10,000 feet in Quito, Ecuador.
I would challenge the 10000 foot rule as arbitary. I would contend that it was obtained from emperical evidence. It is necessarily an imprecise value as evidenced by the acclimatisation of Ecuadorians or the apparent ability of BelArgUSA to fly with unimpaired functions at 14000 feet.
Many thousands of aircrew have flown in unpressurised aircraft and their abilities and functions observed. In a stress free and passive state the rule was that a passenger did not require oxygen until higher than 12500 feet whereas active aircrew needed oxygen above 10000 feet. Certainly moving around the cabin and doing any work, even going to the toilet, was hard work without oxygen.
We had one flight engineer who was sown the back with us with a happy smile on his face. in his own opinion he was 100% AOK. His captain, OTOH was concerned that he had been off oxygen for 20 minutes at an altitude of 15000 feet.
Man is no accurate judge of his abilities when he is hypoxic, just lucky. I am extremely lucky, I feel nauseous and ill long before I sucumb to hypoxia.