Starting the flow of emergency oxygen should:

• A. inflate automatically; if not, the flight deck can activate it with the flip of a switch
• B. be manually activated by a passenger
• C. only inflates if cabin pressure drops
• D. require a separate oxygen canister to be connected by crew

Answer: (A)

Emergency oxygen flow is designed to start automatically when cabin pressure is lost or when the cabin altitude rises to a level that requires supplemental oxygen, so oxygen is available without delay. This automatic activation ensures passengers and crew aren’t left waiting for someone to act. If the automatic system doesn’t engage for some reason, there's a backup control in the cockpit that can be used to manually start the flow with a switch. That combination—automatic deployment plus a manual override—is what keeps everyone breathing safely during a decompression.

The other possibilities don’t fit because relying on a passenger to activate oxygen isn’t how these systems are intended to work, oxygen only inflating in response to pressure changes isn’t the sole trigger in all designs, and emergency oxygen doesn’t require crew to connect a separate canister in normal operation.