Area Navigation Systems: Present Performance and Future Requirements

Abstract

Area Navigation (RNAV) is a concept that enables an aircraft to fly directly from desired origin to destination without the need to overfly VORTAC stations. Area navigation systems include primarily VOR/DME dependent systems, although self-contained systems (such as INS) and hyperbolic systems (such as OMEGA) are also included as part of the overall concept. These systems may also include a vertical capability (VNAV or 3D) and time control along a flight path (4D). The current use of RNAV in the National Airspace System (NAS) includes a number of routes and procedures and airborne systems with a wide range of features and capabilities. Unlike many of the elements of the upgraded Third Generation ATC system, RNAV does not require any major technological developments. However, to achieve the full benefits of RNAV, a phased implementation plan is required that is favored by the users and manufacturers and the FAA. An Area Navigation Symposium of February 1972 revealed diverse interpretations of the capabilities, limitations, and benefits of this concept. Subsequently, an FAA/Industry Task Force was formed and the recommendations of this group, the RNAV Task Force Report [l], provided a three-phased implementation plan which includes specific recommendations for both ground and airborne systems. This report also raised a number of interrelated issues which must be resolved prior to the development of new avionics standards or other system planning documents, and ultimately, the full-scale implementation of area navigation. The primary impact of the Task Force recommendations result from increasingly stringent system accuracy and functional requirements, both enroute and in the terminal area. These requirements, when viewed in total, suggest the necessity of a close examination of RNAV system error elements and related avionics issues. Each of these issues impacts any attempt to quantify avionics standards, separation standards, and ground system NAVAID support. This paper presents some preliminary results of an effort to provide substantiating data for the Task Force recommendations. The specific area that is addressed is the performance of area navigation systems as compared to present and recommended future requirements. Very limited flight test data have been obtained thus far, and therefore the results should be interpreted accordingly. The results in this paper do not represent an official policy or position of the FAA, but are presented in the interest of exchanging technical information.