I have a question: Can a planeload of passengers be disabled by action from the cockpit? Meaning, if the a/c becomes depressurized, overhead functioning oxygen masks would automatically drop down. Could they be prevented from doing so; could the oxygen pressure be turned off from the cockpit? (Assuming some kind of mischief up ahead desiring the silencing of passengers and their cellphones.)
No.
But the Pax will most likely run out of oxygen before the pilots do.
(I cannot give you exact numbers because of the following variables:
1. How many passengers are loaded on the aircraft and how many puts on and activates their masks.
2. Oxygen duration for the pilots is also dependant on the amount of crew (2/3/4) and the setting of their mask. 100% or not. EMER or not.)