Garmin G1000 NXi Reference Manual page 195

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 system stops
navigating in GPS Mode.
DR Mode is indicated on the system by the appearance of the letters 'DR'
superimposed in yellow over the 'own aircraft' symbol as shown in the following
figure. In addition, 'DR' is prominently displayed, also in yellow, on the HSI slightly
above and to the right of the aircraft symbol on the CDI as shown in the following
figure. The CDI deviation bar is displayed in yellow, but will be removed from the
display after 20 minutes. Lastly, but at the same time, a 'GPS NAV LOST' alert message
appears on the PFD.
Normal navigation using GPS/SBAS source data resumes automatically once a valid
GPS solution is restored.
It is important to note that estimated navigation data supplied by the system 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 estimating your 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 system through
DR while there is no heading and/or airspeed data available should not be used for
navigation.
DR Mode is inherently less accurate than the standard GPS/SBAS Mode due to the
lack of satellite measurements needed to determine a position. Changes in wind speed
and/or wind direction compounds the relative inaccuracy of DR Mode. Because of this
degraded accuracy, the crew must maintain position awareness using other navigation
equipment until GPS-derived position data is restored.
190-02178-02 Rev. A Garmin G1000 NXi Cockpit Reference Guide for the Cessna NAV III
Abnormal Operation
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