What is the purpose of the "deny feature" on the flight deck door?

The purpose of the "deny feature" on the flight deck door is essentially to prevent unauthorized entry. This feature is a critical security measure designed to maintain the safety and integrity of the flight deck by ensuring that only authorized crew members can enter. By restricting access, it helps to safeguard the cockpit from potential threats, ensuring that pilots can operate the aircraft without interference or risk from unauthorized individuals.

The other options may address aspects of safety or functionality, but they do not specifically capture the primary intent of the deny feature as effectively as the option chosen. Emergency access typically pertains to situations where access might be needed quickly, while the ability to open the door from inside or secure the door during flight are operational aspects but do not encapsulate the primary security focus of the deny feature.