Sensitivity of WAAS LNAV/VNAV Coverage with the New Integrity Monitor Design

Robert Fries, Cheryl Griffith, Eric Altshuler and Stephen Peck

Abstract:	Raytheon is developing the Wide Area Augmentation System (WAAS) under contract with the Federal Aviation Administration (FAA). Raytheon is currently in the process of finalizing the algorithms to be used in the Integrity Data Monitor (IDM). The IDM computes integrity bounds for the WAAS corrections. The algorithms in the IDM are proved safe in that they guarantee that the probability of Hazardously Misleading Information (HMI) being presented to the user of less than 10-7 per approach. This approach is defined to be Lateral Navigation/Vertical Navigation (LNAV/VNAV); an approach procedure that combines a basic vertical navigation capability with conventional non-precision approach lateral guidance. LNAV/VNAV capability requires that the Vertical Protection Limit (VPL) be less than 50m. Raytheon is currently (July, 2001) in the process of algorithm validation of the new IDM. Algorithm validation includes: alarm analysis/mitigation, parameter tuning, performance analysis and timing of the algorithms in the IDM. Alarm mitigation and parameter tuning are chosen to maximize system availability and continuity as long as the probability of HMI meets the 10-7 per approach requirement. As algorithm validation progresses, WAAS LNAV/VNAV availability has been shown to be highly sensitive to some of the features of the new algorithms. These include: ionospheric threat models, Ionosphere Pierce Point (IPP) Coverage, radius size, tuned parameters such as false alarm rate and levels of HMI protection, and general alarming. This paper will give a brief overview of each one of these areas and explore its effect on WAAS LNAV/VNAV Availability.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	575 - 580
Cite this article:	Fries, Robert, Griffith, Cheryl, Altshuler, Eric, Peck, Stephen, "Sensitivity of WAAS LNAV/VNAV Coverage with the New Integrity Monitor Design," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 575-580.
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