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APPENDIX C
Troubleshooting Q & A
215
190-00357-00 Rev E
What does the OBS key do and when do I use it?
The OBS key is used to select manual (OBS mode) or
to suspend automatic sequencing of waypoints. Activat-
ing OBS mode (as indicated by an annunciation
directly above the OBS key) holds your current “active
to” waypoint as your navigation reference and prevents
the GPS from sequencing to the next waypoint. When
OBS mode is cancelled, automatic waypoint sequencing
is selected and the 500W-series unit automatically selects
the next waypoint in the flight plan once the aircraft has
crossed the present active-to waypoint.
NORMAL
(no “OBS” annunciator)
OBS
Automatic sequencing of
waypoints
Manual sequencing-
“holds” on selected
waypoint
Change in HSI does not
affect CDI deflection
Manually select course to
next waypoint from HSI
Always navigates “TO” the
active waypoint
Will indicate “TO” or
“FROM” waypoint
Must be in this mode for
final approach course
Cannot be set for final ap-
proach course or published
holding patterns
When should I use the OBS key to return to auto
sequencing, and what happens when I do?
The most common application for using the OBS key
is the missed approach. The 500W-series unit suspends
automatic waypoint sequencing (indicated by a “SUSP”
annunciation directly above the OBS key; see left) when
you cross the missed approach point (MAP). This pre-
vents the 500W-series unit from automatically sequenc-
ing to the missed approach holding point (MAHP). If a
missed approach is required, press the OBS key to return
to automatic waypoint sequencing and sequence the ap-
proach to the MAHP.
Why won’t my unit automatically sequence to the next
waypoint?
The 500W-series unit only sequences flight plan
waypoints when automatic sequencing is enabled (i.e.,
no “OBS” or “SUSP” annunciation directly above the OBS
key). For automatic sequencing to occur, you must also
cross the “bisector” of the turn you are navigating. The
bisector is a perpendicular line between two flight plan
legs which crosses through the waypoint common to both
legs.