What is the purpose of the oxygen system on a narrowbody, and how is passenger oxygen delivered?

• A. The oxygen system provides emergency oxygen to passengers and crew during depressurization; passengers receive oxygen via automatic masks, and crew have access to on-demand or quick-donning masks as required.
• B. Oxygen is used to pressurize cabin and is delivered through standard seats.
• C. Oxygen is only available to crew.
• D. Oxygen system provides breathable air at all times.

Answer: (A)

When a jet loses cabin pressure, the oxygen system is there to keep people breathing safely. It’s an emergency supply, not the regular source of cabin air, and it’s designed to work during depressurization. Passengers get oxygen through masks that automatically drop from overhead panels, delivering breathable air as soon as they’re placed on the face. These masks use chemical oxygen generators to provide oxygen for a limited time, enough for everyone to move to a safe altitude and don the masks properly.

For crew, the system provides a ready source of oxygen that can be accessed quickly with on-demand or quick-donning masks. This ensures pilots and cabin crew can continue to operate and assist passengers even as the cabin is losing pressure.

The other options don’t fit because oxygen isn’t used to pressurize the cabin, it isn’t delivered through standard seats, and oxygen isn’t supplied to everyone at all times—only as an emergency measure during depressurization, with passenger masks automatically deployed and crew masks available for rapid access.