Business & Commercial Aviation n June 2006 69

P r o d u c t A n a l y s i s

By Archie Trammell

Wise engineers know you never begina new radar design on a clean sheetof paper. You start with a proven

radar, tweak it with state-of-the-art circuitsand components, add some up-to-datefeatures — and hope you didn’t messanything up.

That’s essentially what Garmin radarengineer Troy Simonton and his staff havedone in creating the GWX 68. It started lifeas a King KWX-56/58, which has a longhistory as a good radar. When King becamepart of AlliedSignal and then Honeywell,the KWX-56/58 was sold off to Narco.Garmin acquired it from Narco as the basisfor its entry into the world of airborneweather radar.

As clever engineers do, Simonton firstconducted an exhaustive search of 56/58maintenance history and identified the 10most frequent failures. He and his staffcorrected all of them with more robustcomponents and improved circuitry. Tomake certain they hadn’t overlookedanything, they switched to a more modernflatplate antenna design and a magnetronwith a much higher MTBF. Next, theyreviewed which features have kept the 56/58near the top in the popularity sweepstakesfor 20 years. They retained them and addedseveral more.

The first thing that will grab you whenyou are introduced to the GWX 68 with theG1000 MFD is the display size, 10 wholeinches. Those who have flown glasscockpits for a while will not think it’sunusual, but if you have spent many hourssquinting at radar displays squeezed into thecenter stack of a light twin, you will thinkyou have died and gone to Valhalla or somesuch place. It is huge by comparison. Andwhen displaying radar data it’s unclutteredwith other stuff, such as a compass rose,waypoints, ETA, TAWS, CAS and whatnot.Just radar data. Some non-radar infor-mation is discreetly arranged around theperiphery, out of the way of what’s reallyimportant. Wonderful!

Another great feature is transmittedpower — it’s 6,500 watts nominal. Thenearest competitor is only 4,000 watts. Toequal GWX 68 power, you will have to payroughly $10,000 more.

What does high power do for the pilot? Itallows the use of a fixed-transmission timeper pulse, which results in consistentperformance at all normal displayed rangeselections — consistent performance interms of weather penetration capability,detection of smaller rain droplets, and rangeresolution. It also reduces the amount ofcircuit hocus-pocus that can do bad thingsto your bank account.

But note we said “the normal displayedrange selections.” Garmin engineers haveadded a displayed range of only 2.5 nm,coupled with a reduced transmission time ofonly one microsecond. You may question thevalue of a 2.5-nm look-ahead, since mostlight twins and turboprops cover 2.5 nm inunder a minute when en route and just overa minute in terminal areas. That gives pilots

little time to begin an avoidance maneuver.The advantage of a 2.5-nm displayed rangeis in the scaling effect. You will appreciate itfirst time you are in a rainy terminal areapicking your way around little rain shafts.Thunderstorms as small as 1,800 feet indiameter have caused major accidents. Whenminimum displayed range is five nm, a 1,800-foot rain or hail shaft is so small on the displayyou may overlook it. But on a 2.5-nm displayit’s twice as big. Plus, that one microsecondpulse results in a 400-percent improvementin range detail, compared to the normal pulseof four microseconds.

Features and BenefitsBeyond those pluses, the GWX 68 hasmany other features, some of which will benefit pilots, some of which willbenefit radar salesmen more than pilots.In the former category, the wisest thing(after that 2.5-nm range) Garmin’sengineers have done is add Vertical Scan.This feature f i r s t appeared on o ld

Garmin’s NewGWX 68 Radar

They began with a solid foundation and designed up.

The GWX 68 is an over-the-horizon radar. This is at 9,500 feet agl. Line-of-sight distance is 97 miles, butstrong echoes are detected at 110 nm. One hit is at 120 nm. Why the line of echoes out toward 11o’clock? The great plains effect. In the Midwest United States, section lines run north-south/east-west.Houses, barns and towns are all gathered along those section lines. Radar picks them up clearly.

Pho

togr

aphy

cou

rtes

y of

Gar

min

Reproduced with permission. Copyright The McGraw-Hill Companies 2006From the June 2006 issue of Business & Commercial Aviation magazine

70 Business & Commercial Aviation n June 2006

Bendix/AlliedSignal RDS series radars yearsago as Vertical Profile. For unknownreasons, the innovators never adequatelyexplained what it’s good for. Actually, it issuch a great addition to any radar it’samazing other manufacturers haven’t pickedup on it. (You can get something similar if

you have a spare $200,000 lying around.)Why so great? First, Vertical Scan reveals

the altitude structure of storm cells. It is wellknown to scientists that cells exhibiting avery high reflectivity up around 25,000 feet(in the United States) are the ones most likelyto contain extreme rain, hail, microbursts

and perhaps a tornado or two. VS (asGarmin prefers to call it), which commandsthe antenna to sweep vertically through a 60-degree arc, will show where the high reflec-tivity is with the touch of a couple of buttons.A second plus is the extended look-up capa-bility VS gives you. With normal tilt you canlook up only 15 degrees. That is inadequatein several parts of the world (the U.S. West,for instance) where the base of storms maybe at 5,000 feet to 10,000 feet. VS scansupward 30 degrees.

Sector Scan is another feature they haveadded that’s been around a long time, butonly on radars costing three to four timesthe price. Garmin practiced a hefty bit ofone-upmanship on this feature. In mostcases, high-priced competition simplyreduces the scanned sector from 120 degreesto 60 degrees. GWX 68 scanned sectors canbe 20 degrees, 40 degrees or 60 degrees, plusthe normal 90 degrees. The scanned sectorcan also be displaced left or right of straightahead. This, of course, can be helpful whenmaneuvering in terminal areas. It allows youto search into turns. Since the scannedsector is reduced, the update, or refresh rate,is much faster, as fast as 54 looks perminute, compared to a normal 12.

A WATCH feature has been incor-porated . Those who have f lownRCA/Sperry/Honeywell radars will knowit as REACT. Collins has PAC. What itdoes in the instance of the GWX 68 is turnon a grayish background where the display

P r o d u c t A n a l y s i s

www.AviationNow.com/BCA

Frequency X-Band (9375 MHz)

Power Output Nominal . . . . . . . . . . . . . . 6.5 kW

Pulse Length 5 – 320 nm . . . . . . . . . . . . . 4 ms2.5 nm . . . . . . . . . . . . . . . . 1 ms

Power Required 2A/28 VDC

Antenna Size 10-inch or 12-inch phased array

Antenna 12 inch . . . . . . . . . . . . . . . . . 7.8ºBeam Widths 10 inch . . . . . . . . . . . . . . . . . 9.0º

R/T/A Size 10-inch antenna, 9 pounds12-inch antenna, 9.1 pounds

Scan Angle 90º

Scan Rate Full sweep . . . . . . 2 looks/minute60º sweep . . . . . 18 looks/minute40º sweep . . . . . 27 looks/minute20º sweep . . . . . 54 looks/minute

Tilt Range ± 15º

VS Sweep ± 30º

Selectable Modes SBY, WX, MAP, VS, SECTOR

GAIN G1000 MFD . . . . . . -28 to +12dBControl Range G200 . . . . . . . . . . . -28 to +3.5dB

Performance 12-inch antenna . . . . . . . . 217dBIndex 10-inch antenna . . . . . . . . 214dB

STC Range Extended . . . . . . . . . . . . . .80 nm

Display Size 6- or 10-inch diagonal

Displayable Ranges G1000 . . . . . . 2.5, 5, 10, 20, 40,60, 80, 100, 120, 160, 240, 320

MX200 . . . . . . . . . 2.5, 5, 10, 20,40, 80, 160, 320

Stabilization ±30º

Indicator Weight G1000 . . . . . . . . . . . . 6.5 poundsMX200 . . . . . . . . . . . .3.1 pounds

MPEL 12-inch antenna . . . . . 10.83 feet10-inch antenna . . . . . . . 9.2 feet

Pressurization None required

TSO C63C

Interface Outputs ARINC 429/453

Garmin GWX 68 Specs

The G1000 displays radar data as it ought to be displayed: big and uncluttered with other stuff. It’s ona 10-inch MFD. Engine data are stacked on the left. Com frequencies, nav data and nav frequenciesare arranged across the top. The remainder of the space is for radar — unless you’d prefer TAWS, CAS,maps and other stuff rather than radar. At this time you can’t have radar and other stuff simulta-neously. On the right side is a slot for loading updated data. Ground paint is being displayed here to adistance of 100 nm, notice.

may not be properly calibrated in terms ofcolors. Calibration shifts may occur due tointervening rain or simply long range. Thisis one of those features for the salesdepartment. Pilots must be alerted to thetruth that it doesn’t always work. Thefeature assumes radomes are alwaysproperly manufactured and repaired, arenever blinded by excessive paint and arenever contaminated by heavy rain or ice.Actually WATCH/REACT/PAC try to dosomething all radars do naturally withoutany help from fancy electronics. Run TILTdown to where the radar should be paintingground. Where no ground is painted, don’tplan to go there. A black area behind anecho is a “radar shadow,” caused by anobject so dense radar energy can’t penetrateit. Neither can airplanes.

We must mention that other radars withthis feature have been prone to “TerminalArea Redout.” It occurs when flying at loweraltitudes in moderate to heavy stratiformrain. The entire indicator turns red, makingit impossible to see the most intense areas ofrain. It can be defeated by selecting MAP,but on the GWX 68 that causes displaycolors to switch and color calibrations toshift. Now you don’t know the true intensityof the rain ahead. Not good. It will be inter-esting to fly this radar in heavy rain toobserve if Terminal Redout occurs. If youexperience it, do notify Garmin.

While on features of questionable benefitto pilots, the GWX 68, along with justabout everyone else’s radar these days, has“TARGET ALERT. When you are on ashort displayed range selection, or notdisplaying radar data on the MFD, thesystem will alert you to strong echoes in thefar distance. Problem is, those echoes maybe from weather or they may be reflectionsfrom cities and towns. To determine which,you must go to a longer displayed range andemploy a bit of smarts derived from longuse of the radar and many observations ofechoes in the distance on it.

Let’s FlyFeatures and benefits are interesting, butthe real question is, how well does itperform the basic radar function ofrevealing things in front of you? Thanks tothose wonderful folks at Raytheon inWichita, a new Baron, ready for delivery toa customer, was made available to us so wecould have a look. Lou Johansen, a Baronguru at Raytheon, flew it over to Olathe,Kan., the home of Garmin, for our flight.Although a beauty otherwise, when we sawthe aircraft we noted a blemish for radartesting purposes. Wrapped around thelower portion of its nose was a black stripeand below it a brown finish. Lovely, but notideal for radar performance. When radargoes in, paint stripes and other nose art

should come off. Our recommendation:Make certain your aircraft’s nose is a class“A” radome. That’s after the final coat ofpa int i s appl ied . Otherwise , radarperformance will be compromised. (Wemade note to apply mental allowances onthis flight.)

It was a great day for flying, almostCAVU. You don’t want thunderstormsaround for the initial look at a new radar.Thunderstorms get in the way, becausewhat you must do before punching intoweather is determine how well the systemdetects and paints ground returns. If it’ll dowell on ground objects, and with gooddetail, it’ll do well in keeping you out of abad scene.

As we tax ied out , the f ac t thatwonderfully large display is an MFD madeitself apparent. At power-up we saw noradar, just the airport runway layout.

To see radar data, buttons must first bepushed. Only a piano player will becomfortable at first encounter with a row of12 buttons across the bottom of this MFD,which must be played in tune or the radar

remains silent. Johansen had to help.Before takeoff one has to make certain

the radar is working properly. That’s doneby turning it on, in a weather mode, TILTfull up, then bringing TILT down untilechoes appear. But first you must pushmore buttons to get the radar out ofSTANDBY, which the GWX 68 automat-ically goes into on the ground via anairspeed switch. When it is first turnedfrom off to on, the radar takes about aminute to warm up. It then passed our see-echoes-before-takeoff test very well, so offwe went.

To conduct the evaluation, we askedJohansen to climb to 10,500 feet and flysouthwest toward Tulsa. The wheels werenot in the wells before we realized that big,uncluttered display is a spoiler; one tripbehind it and you will never think of radarthe same way again. Radar performs allsorts of non-weather functions when thedisplay is large and uncluttered, such asnavigation backup, attitude awareness,altitude confirmation and even terrainavoidance. Engine gages are stacked on the

Business & Commercial Aviation n June 2006 71www.AviationNow.com/BCA

Multifunction DisplaysSo, the GWX 68 has a wonderful big display, excellent performance and many usefulfeatures. Are there no howevers? Yes. First, the radar display is an MFD, meaning it hasmany knobs and buttons, which are unnecessary for staying away from thunderstorms.For radar operation you need only four controls — MODE, RANGE, TILT and CALI-BRATION, plus a couple of on/off switches. But on a multifunction display you alsoget multifunction buttons and knobs. On the G1000 MFD we counted 32 buttons andeight dual, some triple, function knobs. That’s the price you must pay for a do-it-allmachine. Which would be OK if controls for radar were more or less conventional. Theyaren’t. To change CALIBRATION you must punch, push and turn. (Or is it turn, pushand punch?) To finesse on TILT and CALIBRATION simultaneously, which is vitallynecessary for properly analyzing a storm and for ground mapping, you must conduct afinger fandango on buttons and knobs.

This MFD is no worse than others we’ve flown and better than some. And certainlythe argument can be made that with practice it all becomes second nature. But anencounter with any MFD is a reminder that when radar is one of its many functions, MFDhuman factors need serious study. Dealing with thunderstorms is a stressful situationat best. When they’re all around is no time to accidentally push a wrong button ortwist a knob in the wrong direction and find yourself looking at the runway layout forKeokuk, Iowa, rather than the magenta monster up ahead. That’s a risk because it isan MFD.

Another consideration (and this is true for all all-glass-cockpit aircraft): What aboutdisplay failure modes? As currently configured, assuming the G1000 system, if theright display fails, you’ve lost radar. Which is no different, of course, than with a stand-alone radar display. In this instance, however, if the left display fails you also lose radar,because vital data on the left must now play on the right. Only someone well versedin theoretical statistics can calculate how relevant that is. Radar use for actual thun-derstorm avoidance is critical only about 10 percent of total flight time. But, no matterhow small the risk may be, it’s twice as high with this setup. Garmin engineers are atwork to resolve that issue.

72 Business & Commercial Aviation n June 2006

left side, where they don’t speak unlessspoken to, with frequencies, speeds anddistances strung across the top.

Radar modes are annunciated alphaacross the bottom. A vertical color bar inthe lower left corner displays five storm“levels” — black, green, yellow, red andmagenta. What do they mean? Blackindicates areas where there is no detectableprecip (but there may be very light rain, oreven dry hail). In green echoes expect lightrain and light turbulence. In a yellow echo,moderate rain and a bumpy ride. In a redecho be prepared for heavy to very heavyrain with severe , poss ibly extremeturbulence and much lightning. In amagenta one you will find intense toextreme rain, extreme turbulence, large hail,tornadoes, microbursts and sometimes allof the foregoing. It must be noted that thehazards possible in an echo are not relatedto the color you are in, but by the highestcolor level indicated. That is, flying in thegreen part of a cell with magenta showingin it elsewhere, you are subject to all themagenta hazards. Magenta is not just wheremagenta is, nor is red just where red is.

When MAP is selected, by the way, thosecolors change to black, cyan, yellow,magenta and blue and the calibration levelsfor each color change.

In the lower right corner of the displayare four readouts for TILT, BEARING,SECTOR SCAN and GAIN. AntennaTILT is displayed as a digital value.BEARING is used to select the centerlinepos i t ion o f e i ther VERTICAL orSECTOR SCAN. Widths of SECTORSCANS are given as FULL or a lesser

numerical value, per the selection. A clever feature is the distances shown on

range arcs at various displayed rangeselections. They are keyed to the displayedrange selected, of course, but switch frommultiples of five to multiples of 10 as appro-priate. The number of displayed rangespossible, 12, is much greater than normalfor other radars. Jet pilots will be pleased todiscover 100 nm is possible, as well as 80 nmor 120 nm.

Pertinent buttons and knobs used forradar control adjustments are on the right,which is where they should be. In thatlocation, the captain’s hand and arm don’tcover up anything vital as he or she reachesacross to make RANGE, TILT and GAINchanges. Radar modes, however, areselected with that array of “soft” buttonsacross the bottom mentioned earlier.(“Soft” meaning they are electronic buttons,not real ones.)

Speaking of adjustments, it’s interestingthat the word GAIN is still used. In truth, aGAIN control on airborne radars disap-peared 20 or so years ago.

Prior to that, GAIN actually variedreceiver sensitivity. No more. Since “digitalradar” came into being, receiver gain is leftat full sensitivity, or just less than full, whileGAIN effect is achieved by varyingthresholds for the colors. Thus, what wasonce a GAIN control is now, in fact, aCALIBRATION control, but still calledGAIN on everyone’s radar.

We like the unique GAIN readout thatGarmin uses. It is a blue horizontal bar.When the control is at the calibrated value,the readout properly says CALIBRATED.

Makes sense. Take it out of CAL and theword goes away, to be replaced by a tickmark across the blue bar, with a smalltriangular indicator. Turn a knob in thelower right corner of the MFD clockwiseand the blue bar grows to the right, indi-cating a higher value. The tick mark remainsat CALIBRATED, so you know how muchyou’re increasing CAL. Turn counter-clockwise and the blue bar moves left of thetick mark, indicating lower values. Whatdoes that do? Higher values cause echoes toappear stronger than fact; lower values causeechoes to appear weaker than fact. How canthat help? Suppose you see a red echo. Redmeans it’s either a strong or very strongstorm, a huge difference in how close youshould get. So which is it? Tweak CALI-BRATION higher — to the right. If youbegin to see magenta in the echo after just asmall tweak, it’s a very strong storm. You aremuch too close. It will have very heavy rainin it, may even contain hail. If it takes a lot ofincrease before you see magenta, it’s onlystrong. Don’t get any closer.

But always return the system to CALbefore doing anything else. Otherwise youmay make a fatal mistake.

As stated earlier, several things aredisplayed full time around the edges of thedisplay, where they don’t get in the way. Butin addition to radar, the major area of theright display will display maps, CAS, TAWS,NEXRAD, StormScope, nav data and onand on. Currently, when any of that stuff isbeing displayed, you can’t have radar; whenyou have radar you can’t have any of thatstuff. That’s not all bad, but stay tuned.

The ‘What If” FactorThe most important question in aviation is"What If?" If you have thought about whatcan happen and how to cope before ithappens, it won't be an emergency. So,“what if” this radar fails? The possibility ofthat happening should be low, because thebasic system is a mature design growing outof the KWX-56/58. If a failure does occur,it should be a brief problem. Garmin isaware that breaking into the airborneweather radar market is high risk. SinceRockwell Collins and Honeywell are so welldug in, only giant killers have a chance.Therefore, Garmin plans to keep customershappy. Field repairs are not authorized.Instead, spares will be placed in strategiclocations. Suffer a failure and a loaner willgo in your aircraft within hours.

Your radar itself will go to Olathe wherethe people who built it will ensure it isrepaired and tested thoroughly beforereturn. We assume that procedure will alsoapply to the MFD. So, as is true for any newradar, even one based on an earlier design,failures there will be, but Garmin has a plan

P r o d u c t A n a l y s i s

www.AviationNow.com/BCA

BCA • ISSUE: June2006PAGE: 72 / Version: #1

VS (formally known as VP) is a major benefit to pilots. Users will be surprised how often VS shows noweather from their altitude down, but strong weather above them. Vertical scan is ±30 degrees. Hereno weather, just ground is being depicted, illustrating that VS can also be used to maintain a level deckattitude – in case all else fails.

to ensure they are not overly vexing. Plus,we predict the up-to-24-hour downtimewill be shortened to almost instantly. Whenthe GWX 68 finds its way into air taxi andscheduled operations, as it surely will, that24-hour AOG gap will become a no-no.

Your radar itself will go to Olathe wherethe people who built it will insure it isrepaired and tested thoroughly beforereturn. We assume that procedure will alsoapply to the MFD. So, as is true for any newradar, even one based on an earlier design,failures there will be, but Garmin has a planto insure they are not overly vexing. Plus,we predict the up-to-24-hour down timewill be shortened to almost instantly. Whenthe GWX 68 finds its way into air taxi andscheduled operations, as it surely will, that24-hour AOG gap will become a no-no.

Performance and MoreNow back to the flight. It didn’t take morethan 5 minutes to discover this is a verycapable radar. Climbing out we selectedWEATHER, which is annunciated in theupper left corner of the display, and ranTILT down. At 4,000 feet agl the radardetected ground returns to 80 nm. At thataltitude the horizon is only 63 nm away, sothe radar was reaching out across thehorizon to pick up buildings on the otherside of the world. At 6,500 agl, red echoeswere showing at 100 nm, which is 19 milesbeyond the rim of the earth at that altitude.And there aren’t many tall buildings in littletowns between Kansas City and Tulsa.Note that performance was in spite of theblack stripe and brown paint on the radome.Very, very good.

Echoes we saw at 100 nm and beyond,emphasized another advantage of highpower. It enabled use of a short pulse, evenat long displayed ranges, so echoes frombuildings were displayed as thin slashes.That instantly identifies them as groundobjects. A low-powered radar would havebeen displaying ground objects as fat blobs,due to range smearing, making themdifficult to distinguish from weather.

On the return to Olathe we worked withthat 2.5-nm range selection for severalminutes. We couldn’t quite count individualhouses in the Olathe suburbs, but almost.When they get a look at this radar, heli-copter pilots in particular are going to starta revolution in the front office. They willdemand a 2.5-nm displayed range on alltheir radars. As noted above, fixed-wingpilots who are sometimes forced to fly inareas of rain, plus embedded thunder-storms, will also bow down to the engineerswho created a 2.5-nm displayed range forthem. You can have that feature with otherradar systems, but it’ll cost you severalthousand dollars more.

Applications and PriceApplication potential of the radar is just shortof huge. Since the GWX 68 is built on thesame frame as the KWX-56/58, it will goonto anything that radar went on. The list isalmost endless. Included are all aircraft thathave, or could have, a Bendix RDR-160,230HP, RDS-81/82, RDR-2000/2100, SperryWeatherScout II and on and on. In sum, allsingles with a pod-mounted radar, almostany helicopter, light twin, turboprop or smalljet. Garmin’s current market and aftermarketprospects should have the sales departmentsmiling for years.

Also, avionics shops now have anotherproduct to offer, but evidently not soon. Asthis is being written, to get the package weflew, with that wonderful big display, you’llhave to buy an entire, new-from-the-factory aircraft. If you’re not in line for onealready, it’ll be awhile before you can getone; the first are just coming off productionlines. The G1000 MFD with radar isn’toffered for field installs — yet.

If you’ll settle for the GMX 200 MFDdisplay, you’d best get in line for the radarsensor add-on pronto. We had to wait twomonths before Garmin could find anaircraft with a GWX 68 in it for us to fly.That may have changed by now. Whatabout opting for a non-Garmin display?Garmin says no, but it’ll happen.

Cost is open and shut. If your bankaccount is ready for a new aircraft, you canhave the deluxe, big display version —eventually. Price for the package will befrom $450,000 through $2 million or so.Otherwise the question of cost hinges onwhat you want to play radar data on. Thetransmitter/receiver/antenna section alone(most say R/T/A) is $20,995 with 10-inchantenna for pod mounts and $21,995 with12-inch antenna for everything else. That’sbelow all other airborne weather radars inthe market. Garmin is pushing a new GMX200 MFD for radar display in new or oldairplanes. It’ll also display data from severalother systems; it just depends on how muchyou have got to spend. The basic GMX 200is $14,995. They also still talk about havingan MX 20 for $12,995, but we detected littleenthusiasm for selling you one.

Bottom line? Troy Simonton and hisengineers didn’t mess anything up. Andthat’s how success is measured in the radarengineering world.

Next we want to fly a GWX 68 in heavyweather. Garmin promised. B&CA

Business & Commercial Aviation n June 2006 73www.AviationNow.com/BCA