APPENDIX C
Troubleshooting Q & A
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190-00357-00 Rev H
minal mode to approach mode. CDI scaling is tightened
from 1.0 NM full scale deflection to either 0.3 NM or 2°
full scale deflection whichever is less at the FAF. The scal-
ing change occurs gradually over a 2 NM distance and is
completed before crossing the FAF.
If Vectors to Final is selected, the unit provides CDI
scaling appropriate to the approach, which is typically ±2
degrees angular from the origin of the approach. This an-
gular course deviation reaches the max ±1 NM deviation
at approximately 27 NM from the MAP. The course width
and angular deviation for GPS approaches are similar to
what is provided for VHF localizer signals. (see the fig-
ure – Full-Scale deflection and defined path for VTF ap-
proach).
If a missed approach is executed, the CDI scale will
change to ±0.3 NM or ±1.0 NM, as described in Section
5 - Procedures - Flying the Missed Approach.
Full-Scale deflection and defined path for normal 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.
Full-Scale deflection and defined path for VTF approach
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).
CDI Comparison: GPS vs. VOR
