This document describes one of the airborne components defined in ARINC Specification 631, "VHF Digital Link Implementation Provisions". The intent of this document is to provide general and specific design guidance for the development and installation of the airborne equipment. As such, this guidance covers the desired operational capability of the system and the standards necessary to achieve interchangeability of the hardware. The VHF Data Radio (VDR) has various modes of operation which are described more fully in Chapter 3.

Equipment manufacturers should note that this document aims to encourage them to produce maintenance-free, high performance equipment. They are at liberty to accomplish this by the use of design techniques they consider to be the most appropriate. Their airline customers are more interested in the end result than in the means to achieve it.