What must be tested as part of the preflight check for the Interphone?

The preflight check for the Interphone must include testing all LED lights and communication clarity to ensure proper functionality of the system. This comprehensive check is critical because the Interphone system is used for both internal communications among crew members and making announcements to passengers through the public address system.

By checking all LED lights, crew members can confirm that the device is powered on and operational, which is essential for safety and efficiency throughout the flight. Additionally, assessing communication clarity ensures that messages can be transmitted and received clearly, which is vital in emergency situations and for everyday operations. Testing only specific functions or components, such as just the PA function or the emergency function, would not be sufficient to validate the reliability and performance of the Interphone system as a whole. Battery life, while important for the overall operation of the intercom system, is not typically a primary focus during the preflight check unless there are known concerns regarding battery performance.