What are the limitations on cockpit door operations during flight?

Cockpit door operations during flight have specific safety protocols that are essential for maintaining security and preventing unauthorized access. The correct answer highlights that the cockpit door must remain secured during flight. This policy is in place to protect the flight crew and the aircraft from potential threats, providing an additional layer of security against acts of hijacking or interference. By ensuring that the cockpit door is secured, the integrity of the cockpit is upheld, allowing pilots to focus on their responsibilities without distraction or concern for unauthorized entry.

In contrast, other options suggest that the door should remain open or that it can be locked during flight. Keeping the door open would compromise the safety of the cockpit, while locking it may imply a level of restricted access that could hinder communications or emergency procedures if needed. The option implying no limitations fails to acknowledge the critical safety measures that are standard practice for cockpit operations.