This document sets forth the air transport industry's recommended standards for a digital frequency selection (DFS) system.

Information transfer by means of ARINC Specification 429, "Mark 33 Digital Information Transfer System (DITS)," is assumed for the DFS System.

With the exception of navigation receiver controls, most of the frequency and function selection systems in the past were federated systems, i.e., one control unit per receiver. Available technology and the 2X5 tuning method made federated systems attractive. However, application of digital technology and interfaces permit various degrees of control integration in newer systems.

This document addresses two opposite ends of the DFS integration possibilities, i.e., a totally centralized and a federated system. This is necessary to assure that the radio interface specifications are adequate to cover a range of DFS integration.

It is recognized that actual application of the DFS system will be between federated and centralized concepts. Typical applications deviating from the basic concepts of Figures 2- 1 and 2-2 are illustrated in Attachment 2.