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The GPS 155XL works in conjunction with a set of external switches and your
HSI (OBS) to fly GPS approaches. The external switches are used to control GPS func-
tions, and contain illuminated annunciators to indicate when functions are active.
Your installation must also have annunciators for waypoint arrival and GPS messages.
The NAV/GPS switch determines which data (GPS or NAV1) will be displayed on
the HSI and used by the autopilot/flight director. The current selection will be
indicated by an annunciator light. If power to the GPS 155XL is lost, the system
will automatically revert to NAV1.
The GPS APR switch is used to arm or deactivate an approach, and indicates the
current approach phase status (‘ARM’ or ‘ACTV’). The GPS 155XL will automati-
cally arm a selected approach 30 nm from the airport. If the pilot wishes to termi-
nate the approach or fly the missed approach, the GPS APR switch may be pressed
to disarm/deactivate the approach at any time and return the CDI scale sensitivity
to the 1.0 nm setting. The GPS APR switch may also be used to re-arm the
approach at any time before reaching the FAF. If the selected approach is disarmed
before the FAF, the unit will prompt you to re-arm the approach 3 nm before the
final approach fix.
75
Arm Approach Mode
The external GPS APR switch will automatically
be set to the ARM position 30 nm from the desti-
nation airport. Once the approach is armed, the
unit will provide a smooth transistion from the 5.0
to 1.0 nautical mile CDI scale, and down to 0.3
nm within 2 nm inbound to the FAF. If the
approach is manually disarmed, it may be re-
armed at any time (before reaching the FAF) by
pressing the GPS APR switch.
SECTION
5
APPROACH NAV
GPS Approach
Switch
GPS APR
ARM ACTV
GPS APR
ARM ACTV
NAV GPS
NAV ACTV
NAV GPS
ARM GPS
GPS APR
CTV
155xlb manual 1/12/99 4:06 PM Page 75