Final answer:
The FLT Interphone is used by flight crew for critical communication related to the operation and safety of the aircraft, whereas the SERVICE Interphone is used by cabin crew for in-flight service coordination and ground crew communication during maintenance.
Step-by-step explanation:
The difference between FLT (Flight) and SERVICE Interphone lies in their purpose and usage within aircraft communications systems. The FLT Interphone is used by flight crew members, such as pilots and co-pilots, for intra-cockpit communication, as well as for communication with the cabin crew via a selective calling system. This interphone system is critical for the operation of the aircraft, allowing for the exchange of information related to flight management and safety. On the other hand, the SERVICE Interphone is a system designed for communication among cabin crew members and between cabin crew and ground personnel. It is primarily used for coordinating in-flight service tasks, such as meal distribution or addressing passenger needs. It may also be used for maintenance coordination when the aircraft is on the ground.