This document sets forth the desired characteristics of an aviation satellite communication (Satcom) system intended for installation in all types of commercial transport and business aircraft. The intent of this document is to provide general and specific guidance on the form factor and pin assignments for the installation of the avionics primarily for airline use. It also describes the desired operational capability of the equipment to provide data and voice communications, as well as additional standards necessary to ensure interchangeability. This Characteristic specifies equipment using Inmarsat satellites operating in L-band. Ku-band and Ka-band equipment is specified in ARINC Characteristic 791.