GPS For Precision Approaches

Robert Lob, Young C. Lee

Abstract:	The Global Positioning System (GPS) has been tested and evaluated by many different organizations and countries, and it is now generally accepted that GPS can meet the accuracy requirements for all phases of flight up to and including nonprecision approaches. Approaches within the National Airspace System (NAS) is classified as nonprecision if no vertical guidance is provided during the approach and landing. However, for use in NAS, there are other requirements such as Integrity and availability/ continuity of service, which are areas being investigated by the FAA. In addition, there is very little information and test data to show the performance of augmented GPS, and whether their combined accuracy can meet the requirements for precision approaches. Currently, many different augmentations are being investigated to determine their capabilities, and the role of these augmented GPS to satisfy navigation In the NAS. This study identifies the precision approach requirements and compares them with the different augmentations of GPS. The results show that augmented GPS can almost meet the accuracy requirements of the first level of precision approaches (i.e., Category I), but may need additional verifications for approaches coupled to autopilots. However, the 24 satellite constellation being proposed and implemented by DOD does not satisfy the availability/continuity of service requirements for an area wide system like satellite navigtion. Further studies will be needed to determine the required number of additional satellites. The study concludes that augmented GPS will be useful even if it provides precision approach capabilities less than Category I, however, the primary concern is not only accuracy but also availability if GPS is to be used as the sole means of navigation In the NAS. I?I addition, further work is being performed in the area of GPS real-time carrier tracking algorithms, which show promise for eventually using augmented GPS for Category I+ precision approaches.
Published in:	Proceedings of the 1991 National Technical Meeting of The Institute of Navigation January 22 - 24, 1991 Sheraton San Marcos Hotel Phoenix, AZ
Pages:	321 - 329
Cite this article:	Lob, Robert, Lee, Young C., "GPS For Precision Approaches," Proceedings of the 1991 National Technical Meeting of The Institute of Navigation, Phoenix, AZ, January 1991, pp. 321-329.
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