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Basic Rules of GPS Approaches
The GPS 155XL is the first GPS certified to meet the requirements of TSO
C-129a Category A1. When using the GPS 155XL for non-precision approaches,
you’ll encounter two types of approaches: overlay approaches (based on existing pro-
cedures) 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 GPS 155XL. 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.
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SECTION
5
APPROACH NAV
Basic Rules of
GPS Approaches
CDI Scale ramping during approach.
0.3 nm
30 nm
2nm
FAF
MAP
1 nm
1 nm
5 nm
1 minute
155xlb manual 1/12/99 4:06 PM Page 77