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Basic Rules of GPS Approaches
The GNC 300 is the first GPS/COM certified to meet the requirements of TSO
C-129 Category A1. When using the GNC 300 for non-precision approaches, you’ll
encounter two types of approaches: overlay approaches (based on existing proce-
dures) and GPS approaches (new approaches designed specifically for GPS). The FAA
has approved a large number of overlay approaches, with plans to add as many GPS
approaches as possible to take advantage of the safety and convenience of GPS.
Flying a GPS approach is not difficult, and varies from conventional approaches
only in the operation of the equipment being used. Although you’ll often be following
the same flight path used in conventional approaches, the equipment operation pro-
cedures will be different from typical NDB or VOR approaches.
The following definitions, guidelines and examples that follow will help you
understand the basic rules of GPS approaches, and guide you through some typical
approaches. Think through the approach examples— this will assist you in getting
the greatest benefit from the GNC 300. There are a few basic rules that apply to all
GPS approaches. Remembering these rules will assist you in understanding the
approach procedures and ensure the greatest margin of safety for your flight.
• The approach to be flown must be in the aviation database, and the database
must be current.
• You may select an approach any time after the destination airport is selected.
If the GPS APR switch does not indicate an ‘ARM’ status within 2 nm inbound
to the final approach fix, you run the risk of flying a non-approved approach.
• When performing an approach, the GPS SEQ switch must be set to the AUTO
position with the FAF as the active to waypoint for the approach to go active.
If the switch has not been set to the AUTO position 2 nm before the FAF, the
CDI scale transition will be compressed, making the CDI change more abrupt.
(continued on the next page...)
75
APPROACH NAVI-
GATION
GPS SEQ Switch
CDI scale ramping during approach.
0.3 nm
30 nm
2nm
FAF
MAP
1 nm
1 nm
5 nm
1 minute
SECTION
6
APPROACH NAV
Basic Rules of
GPS Approaches
300 7/14/98 8:50 AM Page 75