During depressurisation, when PSU oxygen is deployed, which action is performed first?

• A. Return to your seat and fasten seat belt.
• B. Complete non-normal depressurisation checklist.
• C. Call the flight crew to report the event.
• D. Initiate an emergency descent PA.

Answer: (B)

In-flight depressurization requires following a non-normal depressurisation checklist. This ensures the crew respond in a coordinated, priority-driven way, preserving life by immediately addressing oxygen needs, establishing communication, and planning an emergency descent in the correct order. The checklist provides the required sequence so actions like notifying others and briefing passengers are handled systematically rather than ad hoc. While returning passengers to seats, calling the flight crew, or issuing a PA are important parts of the overall response, they come after or within the structured steps of the checklist, not as the very first action.