When the GPS receiver is turned on, it begins an internal
process of test and initialization. When the receiver is
initialized, the user develops the route by selecting a WP
or series of WPs, venues the data, and selects the active
flight plan. This procedure varies widely among receivers
made by different manufacturers. GPS is a complex system,
offering little standardization between receiver models. It is
the pilot's responsibility to be familiar with the operation of
the equipment in the aircraft.

The GPS receiver provides navigational values such as track,
bearing, groundspeed, and distance. These are computed from
the aircraft's present latitude and longitude to the location of
the next WP. Course guidance is provided between WPs. The
pilot has the advantage of knowing the aircraft's actual track
over the ground. As long as track and bearing to the WP are
matched up (by selecting the correct aircraft heading), the
aircraft is going directly to the WP.

GPS Instrument Approaches
There is a mixture of GPS overlay approaches (approaches
with "or GPS" in the title) and GPS stand-alone approaches
in the United States.

NOTE: GPS instrument approach operations outside the
United States must be authorized by the appropriate country
authority.

While conducting these IAPs, ground-based NAVAIDs are
not required to be operational and associated aircraft avionics
need not be installed, operational turned on, or monitored
however, monitoring backup navigation systems is always
recommended when available.

Pilots should have a basic understanding of GPS approach
procedures and practice GPS IAPs under visual meteorological
conditions (VMC) until thoroughly proficient with all
aspects of their equipment (receiver and installation) prior
to attempting flight in instrument meteorological conditions
(IMC). [Figure 7-29]

All IAPs must be retrievable from the current GPS database
supplied by the manufacturer or other FAA-approved
source. Flying point to point on the approach does not
assure compliance with the published approach procedure.
The proper RAIM sensitivity will not he available and the
CDI sensitivity will not automatically change to 0.3 NM.
Manually setting CDI sensitivity does not automatically
change the RAIM sensitivity on some receivers. Some existing
nonprecision approach procedures cannot be coded for use
with GPS and will not be available as overlays.