Garmin GNC420W GPS Receiver User Manual


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4
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ight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.
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y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x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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