How is the Passenger and CC O2 system activated electrically?

• A. By a switch in the flight deck, switching from NORMAL to ON
• B. By automatic altitude sensors only
• C. By the crew pressing a pushbutton in the cabin
• D. By opening the oxygen compartments manually

Answer: (A)

The event is controlled by an electrical control in the cockpit. When the oxygen system switch in the flight deck is moved from NORMAL to ON, electrical power is applied to the passenger and crew O2 system, energizing the oxygen generators and opening the distribution valves so oxygen can be supplied to the masks. In normal operation the system is ready but not energized, and depressurization will trigger automatic mask deployment, but only after the cockpit switch has been set to ON. The cabin pushbutton or manually opening oxygen compartments aren’t how the system is activated; those actions pertain to deploying masks that are part of the already-energized system.