Which procedure should be followed to secure the cockpit during a serious incident?

Following the procedure to implement flight deck lockdown is crucial during a serious incident because it ensures that the cockpit remains secured against unauthorized access and potential threats. Locking down the flight deck helps to maintain control of the aircraft and protects both the flight crew and passengers from escalating danger. This procedure typically involves securing the cockpit door, restricting access, and ensuring that any potential threats are kept away from the critical area of the aircraft.

Implementing lockdown procedures aligns with established security protocols designed to safeguard the crew and passengers in high-stress situations. It serves to prevent any interference from passengers or adversaries, allowing the pilots to focus on managing the incident and ensuring a safe resolution.

While notifying passengers about the situation and controlling cabin access are important, they do not provide the immediate security that a lockdown offers. Cabin doors being locked is part of the lockdown procedure, but it does not encompass the comprehensive measures necessary to secure the cockpit specifically. Passenger movement in the aisles should generally be restricted during serious situations to mitigate risk, further emphasizing the necessity of a lockdown.