Garmin GNC 420 - Manual (Page 58)

GNC 420(A) Pilot’s Guide and Reference
SECTION 3
NAV PAGES
3-24 190-00140-20 Rev. K
Each satellite has a 30-second data transmission that
must be collected (hollow signal strength bar, see Figure
3-48) before the satellite may be used for navigation
(solid signal strength bar, see Figure 3-47). Once the
GPS receiver has determined the current position, the
GNC 420 indicates position, track, and ground speed on
the other navigation pages. The GPS receiver status field
(Figure 3-47) also displays the messages listed in Table
3-5 under the appropriate conditions.
GPS Receiver Status Messages
Searching Sky
The GPS receiver is searching the sky for ANY visible satellites. The
pilot is informed of this status with a ‘Searching the Sky’ message.
Acquiring Sat
The GPS receiver is acquiring satellites for navigation. In this mode,
the receiver uses satellite orbital data (collected continuously from
the satellites) and last known position to determine which satellites
should be in view.
2D Navigation
The GPS receiver is in 2D navigation mode. Altitude data is provided
by an altitude serializer.
3D Navigation
The GPS receiver is in 3D navigation mode and computes altitude
using satellite data.
Poor Coverg The GPS receiver cannot acquire sufficient satellites for navigation.
Rcvr Not Usbl
The GPS receiver is unusable due to incorrect initialization or
abnormal satellite conditions. Turn the unit off and on again.
AutoLocate
The GPS receiver is looking for any available satellite. This process
can take up to five minutes to determine a position.
Table 3-5 GPS Receiver Status Messages
The Satellite Status Page also indicates the accuracy
of the position fix, using Estimated Position Error (EPE),
Dilution of Precision (DOP), and Horizontal Uncertainty
Level (HUL) figures. DOP measures satellite geometry
quality (i.e., number of satellites received and where they
are relative to each other) on a scale from one to ten. The
lowest numbers are the best accuracy and the highest
numbers are the worst. EPE uses DOP and other factors
to calculate a horizontal position error, in feet or meters.
HUL is explained in Section 11.