What is the protocol for locking/unlocking the lavatory door?

The chosen answer indicates that the lavatory door can be locked from the outside, which is a common feature for aircraft lavatories. This is important from a functionality and safety perspective, as it allows crew members to ensure privacy for passengers while using the lavatory. The ability to lock the door from the outside is typically intended for operational procedures, particularly when the aircraft is on the ground or during specific flight phases where access to the lavatories needs to be controlled.

Locking the lavatory door helps prevent unauthorized entry when it is in use, thus respecting passengers' privacy and maintaining comfort. It is standard for aircraft design to include this feature so that flight attendants can manage the situation efficiently, addressing any emergencies if necessary.

Other options describe scenarios that do not align with typical lavatory door protocols or safety measures in an aircraft setting.