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GPS Accuracy
GPS Condition Accuracy Level
Accuracy of the original GPS system,
which was subject to accuracy
degradation under the government-
imposed Selective Availability (SA)
program.
100 meters
Typical GPS position accuracy
without SA.
15 meters
Typical differential GPS (DGPS) posi-
tion accuracy.
3-5 meters
Typical WAAS position accuracy. < 1.25 meters
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.
3. Approach Annunciations
LPV, L/VNAV, LNAV+V, LNAV, and MAPR will appear
in the flight phase annunciation window.
Annunciation Description
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.