Error and Availability Analysis of Category IIIb LAAS Augmented by Radar Altimeter

Curtis A. Shively and Thomas T. Hsiao

Peer Reviewed

Abstract:	The Federal Aviation Administration’s (FAA) Local Area Augmentation System (LAAS), originally designed for Category I (CAT I) precision approach applications, is being evaluated for extension to Category IIIb (CAT IIIb) autoland applications. This paper evaluates the improvement achieved by using the radar altimeter as another ranging source in the position solution for the more stringent CAT IIIb operations. New mathematical expressions are derived for the vertical error standard deviation using satellites and radar altimeter together. For the case of four or more satellites and radar altimeter, the vertical error standard deviation is no larger than the lesser resulting from using either the satellites alone or the radar altimeter alone. Consequently, if satellite geometry is poor, this augmentation can considerably limit the vertical error, depending on the quality of the radar altimeter. Availability results indicate that the contemplated performance of the radar altimeter (with additional terrain data) could significantly improve the availability of LAAS for CAT IIIb.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 52, Number 3
Pages:	155 - 162
Cite this article:	Shively, Curtis A., Hsiao, Thomas T., "Error and Availability Analysis of Category IIIb LAAS Augmented by Radar Altimeter", NAVIGATION: Journal of The Institute of Navigation, Vol. 52, No. 3, Fall 2005, pp. 155-162.
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