On Oct 30, 9:18 am, Stefan wrote:
I've heard that above some altitude, the FARs require the use of an
oxygen mask rather than a cannula in US registered aircraft. Where do I
find this requirement? (FAR 91.211 doesn't mention it.)

Thanks
Stefan

I'm not sure its a FAR but it is a limitation printed on my O2 system.
I assume that limitation is a condition of its certification.

-Robert