GPS Accuracy
GPS Condition
Accuracy of the original GPS system,
which was subject to accuracy
degradation under the government-
imposed Selective Availability (SA)
program.
Typical GPS position accuracy
without SA.
Typical differential GPS (DGPS) posi-
tion accuracy.
Typical WAAS position accuracy.
WAAS Channels
WAAS channel numbers are shown on Airport
Approach pages in the Waypoint page group. The WAAS
approach reference ID is displayed in the top left corner
of the map. The approach service level is shown in the
lower right corner of the map. Service level annuncia-
tions available are: LPV, L/VNAV, LNAV+V, or LNAV.
Accuracy Level
100 meters
15 meters
3-5 meters
< 1.25 meters
3. Approach Annunciations
LPV, L/VNAV, LNAV+V, LNAV, and MAPR will appear
in the flight phase annunciation window.
Annunciation
LPV
Follow lateral and vertical guidance to LPV
minimums.
L/VNAV
GPS approach identified in the database as
LNAV/VNAV. Fly to LNAV/VNAV minimums.
LNAV+V
Non-precision GPS approach with advisory
vertical guidance. Note that some LNAV/
VNAV approaches are not yet marked in
the database as such and will show up as
LNAV+V. If the chart shows the approach
as LNAV/VNAV, it can be flown to LNAV/
VNAV minimums.
LNAV
Non-precision GPS approach or non-GPS
approach, such as ILS or Localizer.
MAPR
Missed Approach, indicates the system is
providing missed approach integrity and
CDI full-scale deflection ±0.3 NM. This also
shows that the pilot has initiated a Missed
Approach by pressing the OBS key after
crossing the MAP.
4. SBAS selection
The SBAS (Space-Based Augmentation System) menu
option allows you to enable or disable the use of WAAS
satellites. If WAAS is disabled, the unit will not be able
to fly vertically guided GPS approaches (LPV, LNAV/
VNAV, or LNAV+V). If WAAS was previously disabled,
it may take several minutes to achieve a 3D-Diff fix after
re-enabling WAAS.
See the section on SBAS Selection of the Setup 2 Page in
the Aux Pages chapter of the Pilot's Guide for more details.
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