An Operational Test And Evaluation Of An Airborne Loran-C Navigator System

Abstract

ABSTRACT The Coast Guard developed a small, lightweight, Loran-C area navigation system for use in its helicopters engaged in offshore operations and tested it at Cape May, New Jersey area during the fall of 1976. The results of the test program which are presented in this paper show a significant improvement in the ability to maintain a desired trackline. The compatibility of the system with both present and planned area navigation routes and procedures was demonstrated for enroute, terminal and final approach operations. Extremely accurate performance in non precision approaches, using previously measured waypoint coordinates, was demonstrated. The built-in telemetry function allowed position monitoring of the aircraft from the operating air station as frequently as desired. Performance was satisfactory for offshore missions where VOR/DME is inadequate which should be of special interest to off-shore helicopter operators. OPERATIONAL TEST PROCEDURES The implementation of Loran-C as the primary navigation system suitable for United States Coast Guard airborne operations requires that several functional, operational and accuracy questions be resolved. In order to organize these questions in a logical sequence and to minimize the effort required to document the performance of the Loran-C navigator, a methodical and comprehensive flight test program was developed. This paper describes the tests and the detailed results of the airborne Loran-C navigator system operational test and evaluation showing compliance with requirements for National Airspace Systems (NAS) operations. Readers interested in the Search and Rescue (SAR) and surveillance testing results should obtain a copy of Reference 4. PROGRAM OBJECTIVES The operational evaluation of the airborne Loran-C navigator system was designed to satisfy the following general objectives: Obtain operational data on realistic Coast Guard Search and Rescue (SAR) missions which can be used to determine the capabilities of the Loran-C system in relation to operational requirements and constraints. Acquire accuracy data using the Loran-C navigator system which documents the absolute accuracy and the statistical error probability for use in Coast Guard surveillance and enforcement missions. Evaluate the suitability of the Loran-C navigation system in the current VOR/DME NAS environment as well as the compatibility of Loran-C with the existing and planned NAS area navigation constraints. Demonstrate the applicability of Loran-C navigation for use where VOR/DME coverage is inadequate, such as in off-shore helicopter operations. NAVIGATION SYSTEM DESCRIPTION The TDL-424 Loran-C navigator system is a miniaturized computer based device designed for aircraft use. Figure 1 is a photograph of the device. The system uses microprocessors for the Loran-C receiver and for navigation computation. The Loran function is completely automatic. The navigation function is based upon waypoints which are entered by the pilot. Using the Loran-C information and the waypoints, the system calculates and displays the following parameters: present position in latitude and longitude or in Loran-C time differences; great circle range and bearing from present position to the selected waypoint; desired and actual track angles, track angle error, ground speed, cross track error, and time to go to the selected waypoint.