Garmin G900X Pilot's Manual - page 324
GPS NAVIGATION
190-00726-00 Rev. A
5-166
Garmin G900X Pilot’s Guide
5.24 ABNORMAL OPERATION
DEAD RECKONING
NOTE:
Dead Reckoning Mode only functions in Enroute (ENR) or Oceanic (OCN) phase of flight. In all other
phases, an invalid GPS solution produces a “NO GPS POSITION” annunciation on the map and the G900X
stops navigating in GPS Mode.
While in Enroute or Oceanic phase of flight, if the G900X detects an invalid GPS solution or is unable to
calculate a GPS position, the system will automatically revert to Dead Reckoning (DR) Mode. In DR Mode, the
G900X uses its last-known position combined with continuously updated airspeed and heading data (when
available) to calculate and display the aircraft’s current estimated position.
‘DR’ is prominently displayed, in yellow, on the HSI slightly above and to the right of the aircraft symbol on
the CDI as shown in Figure 5-160. Also, the CDI deviation bar is removed from the display. In addition, DR
Mode is indicated on the G900X by the appearance of the letters ‘DR’ superimposed in yellow over the ‘own
aircraft’ symbol Lastly, but at the same time, a ‘GPS NAV LOST’ alert message appears on the PFD. Normal
navigation using GPS/WAAS source data resumes automatically once a valid GPS solution is restored.
Figure 5-160 CDI ‘DR’ Indication on PFD
It is important to note that estimated navigation data supplied by the G900X in DR Mode may become
increasingly unreliable and must not be used as a sole means of navigation. If while in DR Mode airspeed and/
or heading data is also lost or not available, the DR function may not be capable of accurately tracking your
estimated position and, consequently, the system may display a path that is different than the actual movement
of the aircraft. Estimated position information displayed by the G900X through DR while there is no heading
and/or airspeed data available should not be used for navigation.