What indicates that it is time to arm the door?

When preparing for departure, the process of arming the door is a critical safety procedure. The correct answer highlights that the arming of the door occurs after a specific announcement has been made, which serves as a clear and standardized signal for crew members to transition the door from its disarmed state to armed.

This process is fundamental to ensuring the safety of both the passengers and crew during takeoff and landing. The announcement acts as a final confirmation step, signaling that all preceding safety protocols and checks are complete, and it is now safe to prepare the door for emergency access if needed.

While the other options involve elements pertinent to flight preparation and safety, such as departure clearance or ensuring all passengers are on board, none of these directly communicate when to arm the door. Instead, the arm door announcement is specifically designed to coordinate this important action, reinforcing the significance of communication in aviation safety protocols.