Garmin GNC 420W Pilots Guide - Page 58

SECTION 3 NAV PAGES 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. 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. Searching Sky Acquiring Sat 2D Navigation 3D Navigation Poor Coverg Rcvr Not Usbl AutoLocate GPS Receiver Status Messages The GPS receiver is searching the sky for ANY visible satellites. The pilot is informed of this status with a 'Searching the Sky' message. 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. The GPS receiver is in 2D navigation mode. Altitude data is provided by an altitude serializer. The GPS receiver is in 3D navigation mode and computes altitude using satellite data. The GPS receiver cannot acquire sufficient satellites for navigation. The GPS receiver is unusable due to incorrect initialization or abnormal satellite conditions. Turn the unit off and on again. 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 3-24 GNC 420(A) Pilot's Guide and Reference 190-00140-20 Rev. K