The GWX 70 Garmin Aviation 21st Century Radar

The GWX 70 Garmin Aviation 21st Century Radar

Garmin now has a truly modern airborne radar. Back in 2006, the company introduced its GWX 68, which was, in several respects, far ahead of its time. However, it was designed on the chassis of a much-older radar, which had actually started life as a King Radio product. The new GWX 70 Garmin aviation is a clean-sheet design by Garmin’s radar engineering staff, under the direction of Joel Andrews.
The major item making it a 21st -Century radar is that it’s engineered around a solid-state pulse generator. Solid-state is a 70-year leap forward, compared to the traditional coaxial or strapped vane magnetron pulse generators of most other radars. Why is this solid-state device so great? First and foremost, frequency stability. The old magnetrons, conceived by the British before WWII, spewed out a garbage of frequencies. Consequently, radar receiver gates had to be wide to hear that mess, then to work hard to pick out their own pulses from all the static – their own voice, as it were. Not so with the solid-state device. It can easily hear itself and ignore all the other chatter and static in cyberspace. As a result, transmitted pulses can be sent out with greatly-reduced power. Instead of the common 5,000 to 10,000 watts of the old days, a mere 40 watts will do with the GWX 70. It has to work a lot less to do its job.
Since it can hear better, the result is a crisper-appearing echo. Not much, but it’s there and the boundaries of each color are more exact. Plus, for your pocket book, solid-state is far more reliable than the heavy old magnetrons, meaning fewer shop visits and expense.
In truth, solid-state pulse generators are not that new; they’ve been around for 50 years in military radars and Collins introduced them in airline-category radars 30 years ago. But, the GWX 70 is the first to employ the device in radars for singles, light twins and smaller jets.
Is there no downside to it? Yes. For a low-wattage solid-state device to send a usable pulse out beyond 90 or so miles, transmission times per pulse must be much greater. To overcome that, Garmin’s engineers used “pulse compression” on the GWX 70, an engineering trick for making a pulse of radar energy act like it’s shorter than it is. Again, it’s ancient high-tech engineering, used in military radars for years, but this is a first for low-end civil radars. On the GWX 70, when a long range is selected for viewing, pulse compression shrinks the echoes down to just a mile in “range smear.” Were it not for pulse compression, echoes would be smeared out to six miles, front to back, making it almost impossible to differentiate weather echoes from terrain when a long display range is selected. Another plus for the advanced engineering that Garmin’s engineers applied to the GWX 70.
Beyond that, the GWX 70 has the usual me-too “features” that have been added to civil airborne radars, by first one then another radar manufacturer, over the past 30 years; integrated R/T/A section from Bendix in the late 1970’s, “WATCH”, an adaptation from Collins’ ancient “PAC” and Honeywell’s “REACT”, and “Doppler Turbulence Detection,” another oldie that Garmin is promoting as though it’s totally new and unique, although it was first introduced by Collins far back in the last century. Most all experienced pilots consider Turb Detection interesting, but useless.
Garmin has even expanded “Doppler” to create a “Ground Clutter Suppression” feature, which has been around, but not really working as claimed, since the Collins WXR 850 of 1985. (Just why terrain features must be suppressed is a mystery anyway; pilots who can’t tell the difference between weather echoes and ground detail, and use that detail for enhanced safety, haven’t got enough gray matter between their ears to be pilots in the first place.)
The GWX 70 has another feature that taps into Doppler: “Altitude Compensated Tilt”. No doubt, it will be made much of by Garmin salespersons, but it’s not just worthless, but misleading. Actually, all radars have “Auto Tilt” – a “Parked Position”, as it were. It’s simply with Tilt set at 0º with 10 and 12-inch antennas and -1º with an 18-inch one. (Incidentally, Garmin’s “ACT” requires a GPS input to function.) It’s called the “parked” position for tilt and is necessary to see radar shadows, which is a positive indication of where the storms are relative to terrain objects.
The GWX 70 has “Extended Range STC”, adopted from the ancient Sperry line, another ancient engineering hocus-pocus that’s simply a reduction, a miscalibration, in the thresholds for the colors beyond 40 or so miles. The result is red echoes that aren’t really red now but will be when you get closer to them. It’s of benefit only for ill-trained pilots who don’t understand that radar energy gets weaker the greater the distance from the source, just like a light gets dimmer the greater the distance from its source.
GWX 70 engineers did pick up a major safety feature along the way: Vertical Profile, an innovation added at Bendix/King in about 1985 and picked up by Garmin for its GWX 68 and 70. VP may be the most valuable new radar feature since flat-plate antennas. Scanning the vertical structure of a storm reveals much about the hazards within it. For example, when there is an echo aloft but nothing below it, or only a weak return down low, you’re looking at a very high risk of having millions of tons of water suddenly dropping on your head. Don’t ever fly under it. Of all the gizmos that have been added to radars over the years, VP is the only feature that actually increases safety.
Another very useful carry-over from older radars is Sector Scan, which has been around for eons. But, beginning with their earlier GWX 68 radar, Garmin added an enhancement that makes it 10 times more useful than in pre-21st Century times. That feature is now carried over to the GWX 70 as “Variable Sector Scan”, meaning you can cause it to scan a smaller sector, down to only 20º, and at virtually any direction you choose. Most likely, only professional aviators will appreciate it, but the ability to choose a Sector Scan down to only 20º and to move it to any of many different sectors is outstanding.
For starters, Sector Scan results in a greatly-increased display update rate. Helicopter operators, who tend to use radar more for navigation than for weather, will just about swoon over it on rainy, foggy nights when trying to pick up a hospital rooftop. And it’ll make navigating to the landing pad on an offshore rig much less sweaty for the petroleum guys and gals. Garmin’s version of Sector Scan is a bravo addition.
In a left-handed sort of way, Garmin’s engineers also deserve a big thanks for making it simple to overcome a major fault on all the newest radars. Missing on the GWX 70 is magenta symbology, to indicate an extremely vicious storm. That’s no fault of Garmin’s. Ten or so years ago, an FAA/RTCA Committee, most likely egged on by radar manufacturers’ legal departments, decreed that magenta may not be used to warn pilots of extreme hazards. Why? Because it’s needed for course lines and such on EFIS displays. Their logic was most likely an assumption that pilots need only see red to know there’s a hazard and turn tail. But pilots must also know what degree and kind of hazard a storm presents. Without that knowledge, how are they to decide how much circumnavigation distance is prudent?
Fact is, when you see red in an echo, research data tells us only that it’s raining, period. Seventy-percent chance is, that red echo’s only a rain shower. However, to make safe avoidance decisions, pilots must know if it’s just light rain or a gully-washer type deluge. And is it only rain, or is it water turned into hailstones? If the latter, are the hailstones small or large? The old magenta, now seen only in course lines on your EHSI, revealed all that. But, the bureaucrats have taken it away from us.
Fortunately, there’s a way to fool the GWX 70’s four-color display into revealing all those critical facts about a thunderstorm. Since radar engineers mess with color calibration to achieve “Extended Range STC,” pilots can do a similar thing to switch the mandated four colors into, in effect, five colors. (Bless the Garmin engineers for making it so easy with their CAL control and display.) The GMX 70 calibration is such that switching from WX to MAP mode causes red to switch to deep blue. So, when you see a red weather echo, switch to MAP for a sweep or two. If deep blue isn’t in that echo, it’s only a shower. If you see any blue, even a little bit, it’s a thunderstorm of at least Level 4 intensity. Add a mile or two to the circumnavigation distance.
What’s the major thing to not like about this radar? It’s another standard fault with all other manufacturers’ radars since about 1975 (the only exception being the Honeywell Primus 440/660/880 series). It has various names, ranging from XXX to WATCH, and it’s an attempt to cause radars to compensate for the attenuation behind an echo. Common logic tells you that a thunderstorm tucked behind a thunderstorm, or detected through rain, will appear weaker than fact.
So, in searching for new and wonderful features, a bright young fellow came up with a scheme to correct attenuation, many years ago. When the idea was presented to a wise old engineer at RCA named George Lucche (before it became Honeywell), he demonstrated that it doesn’t work as theory says, and can even cause echoes to become miscalibrated when a terrain object is detected. Therefore, Honeywell’s Primus series radars (offshoots from RCA) have an OFF switch on their REACT; Garmin’s WATCH on the GWX 70 doesn’t. So, the GWX 70’s feature can cause echoes to be miscalibrated under certain conditions. Fortunately, that misrepresentation is to the safe side, and is only a factor on echoes inside about 35 nm.
Second possibility, if you want to determine whether it’s merely a thunderstorm or if it’s a hail-producing bugger, when you see red in WX mode, reduce the Cal control down to about 1/2 scale. If any red remains, assume it’s producing large hail and avoid it by a minimum of
10 nm upwind, 20 nm downwind – and those distances are from all parts of it, green as well as red.
Compared to other radars that do not display the fifth color, magenta, the ease with which the GWX 70 can be, tricked, – miscalibrated – into revealing Level 5 and 6 echoes is a meaningful and positive safety feature.
One downside to that: The procedure requires careful tweaking of the Tilt and Cal controls. But, the GWX 70 displays on one of Garmin’s several MFDs. (At prices ranging from $16,000 to $30,000 extra – free if it comes with the new aircraft.) On any MFD, radar controls are timeshared with levers, switches, buttons and knobs put there for other purposes, many of which aren’t remotely connected with radar operation.
Therefore, to tweak Tilt and Cal as necessary to sort out rain showers from bad storms, one must first switch knob and button function selections, which requires punching and turning odd things put on the MFD for other than radar use. (For instance, Tilt selection on the prototype unit we flew worked backwards from logic; to raise Tilt you pushed down on the lever, to lower tilt, lift the lever up.) As a result, those with fat fingers, twitchy digits and/or who tend to become flustered in panic situations, may have big fumble-finger problems. The advice is to practice, practice, practice. Which, in fact, is critical advice when operating any radar.
Summing up, Garmin’s 21st century radar is indeed a step forward into another era. At only $22,995 (plus MFD) it has all the features of a 20th century radar, including several worthy ones from Garmin’s earlier GWX 68, plus a solid-state pulse generator, pulse compression for superior echo detail at all ranges, greater reliability, lower maintenance costs, reduced weight and, perhaps most important of all, greater bragging rights over owners of last century radars.

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