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Basic Rules of GPS Approaches (continued)
• If you cross the same waypoint twice in succession during an approach, you
must set the GPS SEQ switch to the HOLD position PRIOR to crossing the
bisector of the course line at the fix the first time (no matter what the cross-
track distance from the waypoint) to prevent the GPS from sequencing to the
next waypoint.
• The HSI course select should always be set 2 seconds BEFORE changing the
GPS SEQ from HOLD to AUTO to ensure the desired course to the next way-
point is settled prior to use by the GPS and give the autopilot sufficient time
to react to the heading change.
• GPS always displays distance to the currently active waypoint. When deter-
mining distance along the approach, use caution to determine the correct dis-
tance from the approach chart.
• For the approach to become active:
• The GPS APPR switch must be set to the ARM position.
• The GPS SEQ switch must be set to AUTO (verify that the GPS APPR
ACTV light is illuminated before descending beyond the FAF).
• You must cross within 2 nm of the FAF along the inbound course to the
final approach fix (keep in mind that the CDI scale will be at 0.3 nm).
• RAIM must be available (the GPS 155 automatically monitors RAIM, and
will display a message if it is not available) from the FAF to the MAP. If
RAIM is not available or becomes unavailable during this leg, the HSI NAV
flag will appear, and you must fly the missed approach procedure.
• When executing a missed approach, you must fly all published procedures
before proceeding to the missed approach holding point on the GPS.
72
APPROACH NAVIGATION
Basic Rules of GPS Approaches
RAIM may be predicted from NAV Menu 2.
Cumulative distance displayed on the active
route page.
155man (GOOD) 7/24/98 1:57 PM Page 72