This document sets forth the desired characteristics of the Iridium Low-Earth Orbiting (LEO) Aviation Satellite Communication (Satcom) System avionics intended for installation in all types of aircraft including commercial transport, business, and general aviation aircraft. The intent of this document is to provide a description of the system components, aircraft interface, and satellite communication functions. It also describes the desired system performance and operational capability of the equipment. This characteristic specifies equipment using the next generation of Iridium satellites (referred to as Iridium NEXT) operating in L band with planned launch starting in 2016 and completed network by end of 2017. The services used on the NEXT network are referred to as Iridium CertusSM. The Iridium NEXT satellite network replaces the Iridium legacy satellite network known as Block 1.