How high can you go in a normally aspirated

[kevin]

Jim is really right about how much oxygen requirements vary by person. Until I got my P, I regularly flew at 12,000 for an entire flight (3 hours plus) without oxygen, and up to 13,500 for periods less than 30 minutes. And anyone who has met me can tell you I am *not* in great physical shape. I have a friend, non-smoker, who *is* in good shape, yet he gets loopy if he flys all day at 10,000', let alone 12...

Individual differences are large here, I think. And erring on the side of caution is certainly best.

Kevin