LORAN C Additional Secondary Factors: Implications for Meeting Required Navigation Performce (RNP) 0.3

David W. Diggle, Curtis Cutright, G. Linn Roth, Chad Schweitzer, Mitchell Narins

Abstract:	"The Federal Aviation Administration (FAA) has been investigating the ability of Loran C to meet Required Navigation Performance (RNP) 0.3 requirements for accuracy, availability, integrity, and continuity. The use of locally measured and/or calculated Loran C Additional Secondary Factors (ASFs) is key to Loran meeting those accuracy requirements for non-precision approach and landing guidance. The Ohio University Avionics Engineering Center (AEC) has been collecting Loran C data for the past two years at six airports situated along the United States East Coast and throughout the Midwest. Flights to these airports have been conducted semiannually (late winter and late summer) in an effort to determine and characterize the behavior of ASFs as a function of seasonal variations and to determine if a single set of ASFs can cover the entire approach area for an airport. At each airport, Loran C data are collected on the ground using all-in-view Loran C receivers with H-field and E-field antennas. WAAS-augmented GPS position data are collected simultaneously for use as a truth reference. Following the collection of data, a number of stabilized approaches (using ILS when possible) are performed at the airfield. These flight paths commonly extend beyond the approach perimeter for the airport due to Air Traffic Control considerations. In the initial stages of this program, all data collected were post-processed to: 1) generate airfield-specific ASFs, 2) produce ASF-corrected Loran C tracks, and 3) determine lateral error information showing the difference between the ASF-corrected Loran C tracks and GPS truthÐthe latter provided by a WAAS-augmented GPS airborne receiver. More recently, the ground and air data-collection systems have been upgraded to allow ASFs to be calculated immediately after the ground data have been collected. These ASFs are then loaded into the all-in-view Loran C receiver aboard the aircraft, the Loran C position data are corrected in real-time, and both raw and real-time ASF corrected data are logged along with WAAS-augmented GPS truth data. This paper will provide a background on Loran C ASFs, and present results showing ASF stability for the various airports over the past two years. The paper will also document available lateral accuracies at each of the airports and give initial estimates of the coverage provided by a single set of ASFs for a given airport."
Published in:	Proceedings of the 61st Annual Meeting of The Institute of Navigation (2005) June 27 - 29, 2005 Royal Sonesta Hotel Cambridge, MA
Pages:	865 - 874
Cite this article:	Diggle, David W., Cutright, Curtis, Roth, G. Linn, Schweitzer, Chad, Narins, Mitchell, "LORAN C Additional Secondary Factors: Implications for Meeting Required Navigation Performce (RNP) 0.3," Proceedings of the 61st Annual Meeting of The Institute of Navigation (2005), Cambridge, MA, June 2005, pp. 865-874.
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