Garmin GNS 530W Pilot's Manual & Reference page 221

When does the CDI scale change and what does it
change to?
The 500W-series unit begins a smooth CDI scale tran-
sition from the 2.0 NM (en route mode) to the 1.0 NM
(terminal mode) scale within 31 NM from the destination
airport (see below). When within 45° of the final approach
course and the FAF is the TO waypoint, the 500W-series
unit switches from terminal mode to approach mode. CDI
scaling is tightened from 1.0 NM full scale deflection to ei-
ther 0.3 NM or 2° full scale deflection whichever is less at
the FAF. The change occurs over 2 NM and is completed
by the FAF, but will be as defined for the approach.
If you are in a missed approach situation and would
like to return the CDI to the 1.0 NM scale, activate the
missed approach sequence by pressing the OBS key after
you pass the MAP and the annunciation in the lower left
of the screen changes from MAPR to TERM, as described
in Section 5 - Procedures - Flying the Missed Approach.
For this to occur however, the course to the MAHP must
be greater than 3° away from the course line to the run-
way. The CDI scale is also 1.0 NM (terminal mode) within
31 NM of the departure airport.
Full-Scale deflection and defined path for normal approach
±
1 NM
FAF
Inbound track to FAF
Full-Scale deflection and defined path for VTF approach
Sensitivity must change from ±1 NM FSD to either ±0.3 NM or
±2° FSD, whichever is less at the FAF. Change occurs over 2 NM
and is completed at the FAF.
Why does my CDI not respond like a VOR when OBS
mode is active?
Unlike a VOR, the CDI scale used on GPS equipment
is based on the cross-track distance to the desired course
in OBS mode, not an angular relationship to the desti-
nation. Therefore, the CDI deflection on the GPS is con-
stant regardless of the distance to the destination and does
not become less sensitive when you are further away from
the destination. For more information on the CDI scale,
see Section 9 - Aux Pages - Setup Page (CDI/Alarms).
APPENDIX C
Troubleshooting Q & A
Origin = 10,000 ft
past MAP
MAP
+350 ft
±2 degree
angular
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