Cirrus Perspective™ by Garmin – Cockpit Reference Guide for the SR20/SR22/SR22T 190-00821-09 Rev. A114Abnormal OperationFlightInstrumentsEISNav/Com/XPDR/AudioAFCSGPS NavFlightPlanningProceduresHazardAvoidanceAdditionalFeaturesAbnormalOperationAnnun/AlertsAppendixIndexDEAD RECKONINGWhile in Enroute or Oceanic phase of flight, if the Perspective™ system detects aninvalid GPS solution or is unable to calculate a GPS position, the system automaticallyreverts to Dead Reckoning (DR) Mode. In DR Mode, the system uses its last-knownposition combined with continuously updated airspeed and heading data (whenavailable) to calculate and display the aircraft’s current estimated position.NOTE: Dead Reckoning Mode only functions in Enroute (ENR) or Oceanic(OCN) phase of flight. In all other phases, an invalid GPS solution producesa “NO GPS POSITION” annunciation on the map and the system stopsnavigating in GPS Mode.DR Mode is indicated by the appearance of the letters ‘DR’ superimposed in yellowover 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 rightof the aircraft symbol on the CDI as shown in the following figure. Also, the CDIdeviation bar is displayed in yellow. 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 validGPS solution is restored.It is important to note that estimated navigation data supplied by the system inDR Mode may become increasingly unreliable and must not be used as a sole meansof navigation. If, while in DR Mode, airspeed and/or heading data is also lost ornot 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 movementof the aircraft. Estimated position information displayed by the system throughDR while there is no heading and/or airspeed data available should not be used fornavigation.DR Mode is inherently less accurate than the standard GPS/SBAS Mode due to thelack of satellite measurements needed to determine a position. Changes in wind speedand/or wind direction compounds the relative inaccuracy of DR Mode. Because of thisdegraded accuracy, the crew must maintain position awareness using other navigationequipment until GPS-derived position data is restored.
