What must a flight attendant do before entering the flight deck if the pilot has left on a single FA aircraft?

The appropriate action for a flight attendant before entering the flight deck, especially in a scenario where the pilot has left the cockpit and the aircraft is single FA (flight attendant) operated, is to block the aisle with the galley service cart. This action helps ensure the safety and security of the flight deck by preventing unauthorized access while the flight attendant is in the process of entering.

Blocking the aisle serves as a physical barrier, which is a critical safety protocol in aviation to safeguard the flight deck. It allows the flight attendant to maintain control over the cabin environment while managing the situation and ensuring that all necessary procedures are followed without compromising safety.

In contrast, immediately opening the flight deck door without taking precautions could expose the cockpit to potential threats. Checking on the passengers is also important but does not directly address the issue of securing the flight deck. Notifying ground control might be necessary in specific situations but is not a prerequisite for entering the flight deck and does not prioritize immediate safety measures. Thus, utilizing the galley service cart to block the aisle is the most appropriate and responsible choice in this scenario.