Originally Posted by
1wife2airlines
One doesn't want to pay for the O2 that one pilot has to suck and the other does pay or tells their pilots not to suck it. More current people might explain the requirements for flight above 410, 450 whatever.
the reg is above fl350 for 135 operators, FL410 for Part 91. At least 1 pilot at the controls must wear secured and sealed an oxygen mask required by this part.
However, I think whether you burn oxygen or more fuel makes it a moot point on the cost. Also, due to COVID some airlines including Delta received relief from the reg up to FL410. I wouldn’t be surprised if the reg changed at some point in the future due to better pressure warning systems, fewer problems with structural failure, and better quick-donning masks.