The SR-4 Expansion Module IISX is a must-have for pilots who need to communicate with multiple people in their aircraft. This module allows you to add up to two additional users to your IISX intercom system, giving you the ability to stay connected with your entire crew. The SR-4 is easy to install and is compatible with all Flightcom IISX intercom systems. With its reliable performance and versatile connectivity options, the SR-4 Expansion Module IISX is an essential tool for any pilot looking to enhance their in-flight communication capabilities.