What is the operational status required for the interphone system?

The correct answer is that the interphone system must be operable. The interphone system is a critical component of in-flight communication among crew members. It facilitates quick and clear communication during normal operations and emergencies, enabling flight attendants to relay important information or coordinate responses effectively.

Having an operable interphone system ensures safety and efficiency, as it allows flight attendants to communicate with each other, the cockpit crew, and can also be used to address passenger needs promptly. An inoperable interphone could significantly hinder the ability of the crew to manage situations that may arise during a flight, particularly emergencies where timely and effective communication is essential.

While the other options suggest various levels of functionality that could impede operations, the requirement for the interphone system to be operable underscores its vital role in maintaining safety protocols and efficient operation within the aircraft environment.