Supplemental oxygen
 

I'm reading far 91.211 and down under (b)(1)(ii) It talks about pilots not having to use them while at or below FL410 so long as they can be accessed and used within 5 seconds or when a pilot leaves the cockpit. When above FL410 is one of the pilots required to put on an oxygen mask at all times? If I'm not mistaken this rule applies to all jets under US registry not just ones used for commercial operations.