This document defines the characteristics of second generation L-band satellite communication system installations including the avionics equipment defined for Iridium and Inmarsat 2G services. This document provides traditional form, fit, function, and interface standards necessary for the installation of Satcom avionics equipment for all types of aircraft. It also provides a description of each envisioned avionics component that would comply with this Characteristic. Supplement 5 removes obsolete service and system provisions, and adds references to ARINC Characteristic 791 for Ku-band antenna installation details.