I have some doubts trying to interpret what follows.
About the oxygen pressure regulator system, the FCOM states:
EMERGENCY pressure selector
[...]
Note:
Overpressure supply is automatically started when cabin altitude exceeds 30.000 ft.
Overpressure supply is available only when the N/100% selector is set on the 100% position.
N/100% selector
100%: The mask delivers 100% oxygen.
N: [….] When cabin altitude goes above 35.000 ft, the air inlet closes and the wearer breathes 100% oxygen.
My interpretation, that I would like to have confirmed, is:
if I have the selector on N at or below 35.000 ft, omitting safety considerations, nothing happens;
if I have the selector on N, above 35.000 ft, the system automatically switches to 100%, but no overpressure is provided (100% is sufficient up to 40.000 ft and the selector is still physically on N).
With the reference to the second bullet, I'm inclined to think that as the FCOM simply states “100% oxygen”, without referring to overpressure, but honestly also supposing an automatic change to EMERG 100% seems quite logical to me.
Besides, unlike 100% configuration, in EMERG 100%, as far as I know, the oxygen should be continuously supplied. Is that correct?
