When should the flight deck door remain closed and locked?

The flight deck door should remain closed and locked once passengers enter and the door is closed. This procedure is crucial for maintaining security in the flight deck, ensuring that only authorized personnel have access, especially after the general boarding process begins. Keeping the door locked during flight protects against any potential threats and enhances the safety of both the crew and the passengers.

The rationale for having the door closed and locked during these times ensures that the flight deck is secure throughout the flight, not just during specific phases such as boarding or taxiing. In practice, while there are protocols for when the door can be opened during certain operations, the standard of keeping it closed and locked during the entirety of the operational flight ensures maximum safety and security.