If power is lost, what will happen to the flight deck door?

The flight deck door is designed with safety mechanisms that prioritize the security of the flight crew and the aircraft. If power is lost, the correct outcome is that the door will automatically unlock due to the failure of the electronic locking system. This ensures that under situations where equipment might fail, emergency access is available to the flight deck. The system is built this way to allow the crew to maintain operational integrity, even in the absence of electrical power.

The other options suggest outcomes that do not align with the design and safety protocols of the flight deck door. For example, the door remaining locked would inhibit access during an emergency, and closing securely would not address the problem of loss of access to the flight deck. Similarly, providing an alarm signal would not be an effective response in terms of physical access needs. Thus, the correct operation during a power loss scenario is that the flight deck door will automatically open, prioritizing the safety and accessibility for the flight crew.