The Use of Raw GPS for Vertical Navigation

J.D. Andrew Graham and P.Eng

Abstract:	The safety benefits of approaches with vertical guidance are well recognised, but this level of service is typically available only at major airports (with ILS) or to aircraft with sophisticated and costly avionics (Baro VNAV). In May 2000, when selective availability was set to zero, GPS accuracy increased significantly. Ionospheric effects are now the major source of error, yet even at the height of the sunspot cycle, vertical accuracy in the order of 8.5 m (95%) is being observed. Studies indicate that raw GPS, with suitable monitoring techniques, is able to meet the certification requirements for VNAV equipment, and in fact outperforms currently certified barometric VNAV systems in terms of accuracy and integrity. Newer TSO C129a panel mount receivers are being designed with analogue hardware to support VNAV, and the aviation databases already accommodate the parameters required to define a vertical path. This paper investigates the concept of using raw GPS altitude data to provide vertical guidance, with integrity, on LNAV-only and LNAV/VNAV approaches.
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:	591 - 599
Cite this article:	Graham, J.D. Andrew, P.Eng,, "The Use of Raw GPS for Vertical Navigation," 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. 591-599.
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