What action should cabin crew take when a threat is assessed as credible?

When a threat is assessed as credible, donning protective equipment and isolating the area is the most appropriate action for cabin crew to take. This response helps ensure the safety of both the crew and passengers by minimizing exposure to potential harm. Protective equipment provides a layer of security against various types of threats, and isolating the area can prevent the situation from escalating or spreading, allowing the crew to manage the situation more effectively.

Utilizing protective equipment also emphasizes the crew's preparedness and training in handling emergencies, enhancing their ability to respond to threats in a controlled manner. This action aligns with established protocols intended to prioritize safety while assessing and managing the threat.

In contrast, other responses such as immediately evacuating the aircraft may not be feasible or safe depending on the nature of the threat and could lead to further complications. Informing passengers to remain calm, while valuable in maintaining order, does not address the immediate safety needs in the face of a credible threat. Similarly, opening air vents does not pertain to direct threat management. Therefore, equipping the crew and isolating the area is the most comprehensive and appropriate response in this scenario.