During depressurisation, which action is typically performed first when oxygen masks deploy?

• A. Complete non-normal depressurisation checklist.
• B. Stand by for passengers to don masks.
• C. Initiate emergency descent PA.
• D. Return to seat.

Answer: (A)

When oxygen masks deploy, the first action is to start and complete the non-normal depressurisation checklist. This checklist provides the required, ordered steps to bring the aircraft to a safe state under pressurization loss, ensuring critical actions are not forgotten or attempted out of sequence. It guides you through confirming oxygen flow, securing crew readiness, communicating as needed, and initiating the descent in a controlled manner. Following the checklist first ensures that oxygen is delivered effectively and that the descent is started promptly in a coordinated, standardized way.

Standing by for passengers to don masks is a later step, because relying on passengers to self-don can delay essential protection. Initiating an emergency descent PA is important, but it follows the initial procedural actions and coordination outlined in the checklist. Returning to your seat would reduce your ability to manage the emergency and assist others, so it isn’t the first action.