What feature of the flight deck door allows for emergency exit if the door becomes blocked?

The feature that allows for an emergency exit if the flight deck door becomes blocked is known as the decompression blow-out panel feature. This panel is designed to alleviate pressure and create an opening in the event that the door cannot be opened due to external circumstances, such as a blockage or damage. The blow-out panel provides an alternative means of escape, ensuring that crew members can exit the flight deck in an emergency without being trapped.

This feature is crucial for safety protocols, as it ensures that even in challenging situations, there is a path for evacuation. While features like collapsible panels, emergency handles, and emergency lighting aids in navigation and recognition of escape routes, they do not specifically address the necessity for an emergency exit from a blocked flight deck. Thus, the correct choice highlights the importance of maintaining crew safety and emergency preparedness in aviation.