Purpose: This document is intended to set forth general guidance for the design and installation of a Barometric Altitude Rate Computer (BARC) for use with a Ground Proximity Warning System (GPWS), This document describes the basic features needed by the users to achieve the desired level of interchangeability.

COMMENTARY: The need for this document emerged during the airlines' preparation of ARINC Characteristic 594 ("Ground Proximity Warning System"), when it became apparent that not all aircraft on which GPWS installations were planned provided a suitable source of barometric altitude rate. However, because this need was less widespread than the need for Characteristic 594, only limited amounts of time and effort were devoted to it. Thus, this Characteristic describes only the essential features of the BARC unit and installation.