How does the captain alert the crew during an emergency?

In an emergency situation, the captain typically alerts the crew through a PA announcement or the interphone system. This method ensures that the message is conveyed directly and clearly to all crew members, who may be spread out across the cabin. The PA system allows for immediate dissemination of critical information regarding the nature of the emergency, necessary actions, and instructions on how to proceed, ensuring that everyone is informed at the same time.

Using direct verbal communication could create confusion, especially in larger aircraft where crew members might not be in close proximity to the captain. Emergency light signals and signal flares are not practical means of communication in the cabin during many types of emergencies that require immediate crew response, as they are designed for other contexts, such as outdoor signaling or visual alerts. Therefore, the PA announcement or interphone is the most effective and efficient way for the captain to ensure that the entire crew receives the alert simultaneously.