Hybridizing: contemporary glide slopes to provide vertical guidance for GPS approaches

Vertical guidance for an instrument approach to landing during conditions of reduced visibility is a crucial element with respect to safety of flight. It is noteworthy that this vertical component, to be most useful and safe, must desirably provide the pilot with no more than several feet of uncertainty. Unfortunately with GPS the vertical portion of the position information supplied to the pilot by GPS signals is the least precise because of the geometries involved. Many aspects of the contemporary UHF glide slope have been studied during its half century of use. This paper reports on advances that make it realistic to claim that a glide slope can be sited for Category I operation at any runway that meets the physical requirements for this type of operation. For the UHF glide slope, siting imperfections are accommodated by using one of five available types of contemporary glide slope systems or derivatives thereof. This paper reviews how accommodations are achieved in practical cases.