Pilot's Guide

190-00749-05 Rev. A
Garmin G1000 Pilot’s Guide for Cessna Caravan
SYSTEM
OVERVIEW
FLIGHT
INSTRUMENTS
EIS
AUDIO PANEL
& CNS
FLIGHT
MANAGEMENT
HAZARD
AVOIDANCE
AFCS
ADDITIONAL
FEATURES
APPENDICES INDEX
315
HAZARD AVOIDANCE
6.2 AIRBORNE COLOR WEATHER RADAR
SYSTEM DESCRIPTION
TheoptionalGarminGWX68AirborneColorWeatherRadarisafour-colordigitalpulsedradarwith6.5
kilowattsofoutputpower.Itcombinesexcellentrangeandadjustablescanningproleswithahigh-denition
targetdisplay.Thepulsewidthisfourmicroseconds(µs)onallrangesexceptthe2.5nmrange.TheGWX68
usesaoneµspulsewidthatthisrangetoreducethetargetssmearingtogetheronthedisplayforbettertarget
definition at close range.
TheCessnaCaravanusesa12-inchphasedarrayantennathatisfullystabilizedtoaccommodate30ºofpitch
and roll.
Tofocusradarscanningonspecicareas,SectorScanningofferspilot-adjustablehorizontalscananglesof
20º,40º,60º,or90º.Averticalscanningfunctionhelpstoanalyzestormtops,gradients,andcellbuildup
activity at various altitudes.
Radarfeaturesinclude:
•ExtendedSensitivityTimeConstant(STC)logicthatautomaticallycorrelatesdistanceofthereturnechowith
intensity, so cells do not suddenly appear to get larger as they get closer.
•WATCH
®
(WeatherATtenuatedColorHighlight)helpsidentifypossibleshadowingeffectsofshort-rangecell
activity,identifyingareaswhereradarreturnsignalsareweakenedorattenuatedbyintenseprecipitation(or
largeareasoflesserprecipitation)andmaynotfullyreecttheweatherbehindastorm.
•WeatherAlertthatlooksaheadforintensecellactivityinthe80-320nmrange,eveniftheserangesarenot
being monitored.
PRINCIPLES OF PULSED AIRBORNE WEATHER RADAR
ThetermRADARisanacronymforRAdioDetectingAndRanging.Pulsedradarlocatestargetsbytransmitting
amicrowavepulsebeamthat,uponencounteringatarget,isreectedbacktotheradarreceiverasareturn
echo.Themicrowavepulsesarefocusedandradiatedbytheantenna,withthemostintenseenergyinthe
centerofthebeamanddecreasingintensityneartheedge.Thesameantennaisusedforbothtransmittingand
receiving.ThereturnedsignalisthenprocessedanddisplayedontheG1000MFD.
Radardetectionisatwo-wayprocessthatrequires12.36µsforthetransmittedmicrowavepulsestotravelout
andbackforeachnauticalmileoftargetrange.Ittakes123.6µsforatransmittedpulsetomaketheroundtrip
if a target is ten nautical miles away.
Airborneweather radarshouldbeusedtoavoidsevereweather,notforpenetratingsevereweather.The
decision to fly into an area of radar targets depends on target intensity, spacing between the targets, aircraft
capabilities,andpilotexperience.Pulsetypeweatherradardetectsonlyprecipitation,notcloudsorturbulence.
Thedisplaymayindicateclearareasbetweenintensereturns,butthisdoesnotnecessarilymeanitissafetoy
betweenthem.OnlyDopplerradarcandetectturbulence.
Airborneweatherradarhasothercapabilitiesbeyondweatherdetection.Italsohastheabilitytodetectand
providedistancetocities,mountains,coastlines,rivers,lakes,andoceans.