1. Throughout this document, the term "Ground systems" is used to refer to all non-airborne systems, that is, systems whose physical location is other than aboard an aircraft. Specifically, "non-airborne" systems as used here comprises both Ground-based systems and the more-recent satellite-based systems; however, we continue to use the term "Ground-based" both for historical reasons and to avoid such awkward expressions as "non-airborne systems" and "Ground-based and satellite-based systems."