How should crew respond if a security threat level 3-4 is indicated?

When a security threat level of 3-4 is indicated, the appropriate response involves prioritizing the safety and security of all individuals on board. Locking the cockpit door is an essential protocol in aviation security, particularly in heightened threat levels. This action serves multiple purposes, including protecting the flight crew from potential threats while also preventing unauthorized access to the cockpit.

At levels 3-4, there is an acknowledgment that the risk of an attack is significant, making it crucial for the flight team to take immediate and effective measures to secure the aircraft. By ensuring that the cockpit is locked, the crew can concentrate on managing the situation and communicating with air traffic control to inform them of the elevated threat level without being distracted or compromised.

Responses that entail alerting passengers or landing the aircraft immediately can create panic or exacerbate an already tense situation. Ignoring a threat level is never a viable option; it disregards the seriousness of the situation and places everyone on board at risk. Therefore, locking the cockpit door aligns with established safety protocols designed to mitigate risks during high-threat scenarios.