Originally Posted by
172_driver
It was
me speculating, based on your information
.
The mystic part is that didn't prevent the pilot becoming incapacitated, hence I was speculating there was no O2 coming to the mask. If the masks are of the same design as airliners - diluter demand - you will still breath air but it won't be enriched with O2.
From memory 100% is selected in operations I have been a flying spanner. Perhaps airliner crew might confirm the drill!
As a side, working on AA aircraft in the 1970's the cleaning of O2 masks was a night stop task, reason: one of 2 man crew had to be masked at cruise altitudes, I think it was above 25000', this was in the days before the boxed sweep on masks as they hung from a lanyard; and also when one crew member left the flight deck.