Garmin GPS 155XL TSO - Manual (Page 88)

• If you cross the same waypoint twice in succession during an approach (e.g.,
the IAF and FAF at the same waypoint, or radar vectors to the FAF), you must
set the GPS SEQ switch to the HOLD position prior to crossing the fix the
first time to prevent the GPS from sequencing to the next waypoint.
• During a GPS approach, keep in mind that your external HSI will display the
same CDI needle deflection and scale as the CDI on the GPS 155XL, which
will transition from 5.0 to 0.3 nm through the approach. Also note that unlike
a VOR CDI, the GPS CDI scale is based on the cross-track distance to the
desired course (the distance to the reference waypoint does not have an effect
on the CDI scale, see illustration left).
• 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 from the currently active waypoint. When deter-
mining distance along the approach, use caution to determine the correct dis-
tance from the approach chart.
• RAIM must be available (the GPS 155XL 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 flying a missed approach, SID or STAR, you must fly all published pro-
cedures and ensure that all printed course and altitude restraints are achieved.
• If you are off course to the MAP waypoint and use a direct-to to re-center the
d-bar, the active approach will be cancelled.
• SUA alerts are disabled when an approach is selected and armed and the air-
craft is less than 30 nm from the destination airport. SUA information is still
available from the NRST key at all times.
78
SECTION
5
APPROACH NAV
Basic Rules of
GPS Approaches
Unlike a VOR, GPS CDI deflection is based on the
cross-track distance to the desired course, regard-
less of how far away you are from the destination.
5 nm 5 nm 5 nm 5 nm
2
nm
2
nm
155xlb manual 1/12/99 4:06 PM Page 78