Garmin G900X Pilot's Manual - page 29

190-00726-00  Rev. A

Garmin G900X Pilot’s Guide

1-17

SYSTEM OVERVIEW

SATELLITE INFORMATION

Satellites  currently  in  view  are  shown  at  their  respective  positions  on  a  satellite  constellation  diagram.  

This sky view is always oriented north-up, with the outer circle representing the horizon, the inner circle 

representing 45° above the horizon, and the center point showing the position directly overhead.  Each satellite 

is represented by an oval containing the Pseudo-random noise (PRN) number (i.e., satellite identification 

number).  Satellites whose signals are currently being used are represented by solid ovals.

The GPS Status Page can be helpful in troubleshooting weak (or missing) signal levels due to poor satellite 

coverage or installation problems.  As the GPS receiver locks onto satellites, a signal strength bar is displayed 

for each satellite in view, with the appropriate satellite PRN number (01-32 or 120-138 for WAAS) below each 

bar.  The progress of satellite acquisition is indicated by signal bar appearance:

• No signal strength bar—Receiver is looking for the indicated satellite.

• Hollow signal strength bar—Receiver has found the satellite and is collecting data.  Each satellite has a 30-

second data transmission that must be collected (signal strength bar is hollow) before the satellite may be 

used for navigation (signal strength bar becomes solid).

• Solid signal strength bar—Receiver has collected the necessary data and the satellite signal can be used.

• Checkered signal strength bar—Receiver has excluded the satellite (Fault Detection and Exclusion; FDE).

• “D” indication on signal strength bar—Satellite is being used for differential computations.

Using  the  current  satellite  signal  information,  they  system  calculates  the  aircraft’s  GPS  position,  time, 

altitude, ground speed, and track for the aircraft (displayed below the satellite signal accuracy measurements 

for reference).  The following quantities denote the accuracy of the aircraft’s GPS fix:

• Estimated Position Uncertainty (EPU)—A statistical error indication; the radius of a circle centered on an 

estimated horizontal position in which actual position has 95% probability of lying

• Horizontal Dilution of Precision (HDOP)—Measures satellite geometry quality (i.e., number of satellites 

received and where they are relative to each other) on a range from 0.0 to 9.9, with lower numbers denoting 

better accuracy

• Horizontal and Vertical Figures of Merit (HFOM and VFOM)—Measures of horizontal and vertical position 

uncertainty;  the  current  95%  confidence  horizontal  and  vertical  accuracy  values  reported  by  the  GPS 

receiver