Avionics Special: Garmins G3X

Meet the Experimental-class EFIS from the Big Boys.


Everyone knew it was a matter of when not if Garmin would enter the mid-cost electronic flight instrument system (EFIS) segment. After all, it has used its corporate horsepower to catch and pass Avidyne and early developer Chelton in the certified races, and you could see the company’s reach starting to head our way. Sure, the G900X, a close cousin of the integrated G1000 system, has been available, and well-heeled builders have looked at the G600 (and now G500) two-screen/one-box systems longingly. But it wasn’t until Cessna announced that its SkyCatcher LSA was getting something called a G300 that the rest of our market looked up to see the big rig with Kansas plates bearing down.

In fact, Garmins first midrange offerings, while adventurous in concept, remain relatively modest as the G3X system wends through its late-beta-test process. As of late January 2010, the G3X was a fully functioning multi-screen, single-ADAHRS (air data attitude heading reference system) setup. Autopilot functions and engine monitoring, both part of the plan from the start, wont be available for testing until later this spring. But Garmin is taking a methodical approach to software development and testing, so while all the features aren’t up and running as this is written, there’s a high likelihood that they will be soon. Its always good to believe that promised features will actually be offered one day.

Is this the best way to use the G3X? We think so…a single screen imposes certain operational limitations.

Digest this Architecture

In many ways, the G3X system resembles the G1000, only simplified. It relies on individual screen modules, called GDU (shorthand, display units) that are linked to the rest of your avionics system with serial connections, both RS-232 (three on each GDU and three on the GSU, or service unit) and ARINC 429 (four on the GSU). Note that the G3X will not support old-school analog connections to nav/coms. Each GDU is linked to a multipurpose module called a GSU 37 through a CAN bus system-a three-wire versatile network.

If the GDU is the face of the system, the GSU is the brain. Inside this 3.5-pound aluminum cube resides the primary ADAHRS unit. The solid-state gyros are rated for 360 of pitch and bank maneuverability at a maximum rotational rate of approximately 200/second. Pitot-static measuring sensors are there, too, though the magnetic sensor (magnetometer) is located remotely, as is the outside-air-temp probe. As the system is currently configured, there are provisions for only one GSU at a time. This follows common practice among the G1000 installations, where single-engine aircraft typically have one set of ADAHRS sensors and rely on other means such as electronic or pneumatic flight instruments for backup. That the components inside the GSU and the software running them are, if not exactly like the certified systems, very close to certified spec should help bolster confidence. Whats more, in my testing of the G3X starting in the summer of 2009, the basic attitude/pitot-static performance has been absolutely rock-solid reliable. Not a glitch, not a hitch…nothing.

Because the G3Xs internal GPS, though a WAAS unit, is not TSOd, if you want to shoot GPS approaches, you’ll need an IFR-approved external box, like the GNS 430W.

While the G3X is underpinned by one GSU module, it can support up to three display units. In fact, when I asked the systems designers about the G3Xs early development it became clear that they felt the minimum system really should have two screens. This philosophy closely shadows G1000/G600 concepts where a main screen (the primary flight display, or PFD) always carries the important attitude information including a horizontal situation indicator (HSI) in the lower part of the screen.

This side view gives you an idea of the display units slim dimensions: 6 inches wide x 7.8 tall and a mere 1.7 inches deep not including the BNC and TNC connectors on the back or the knob on the front.

If you design by the philosophy that one screen ought to be devoted to the PFD, there’s little reason to condense the attitude display or downgrade its abilities to allow for other functions to be presented in that space. In this paradigm, one screen looks ahead as PFD, while a second screen, configured as a multifunction display (MFD) provides the top-down look in moving-map form. By so allocating screen space, the PFD presentation can be clean and elegant-and the G3Xs is. Various pieces of information, including wind speed, navigation source and annunciation, and heading and course-line settings, for example, can be arrayed around and on top of the HSI without clutter. Following G1000 practice, the glideslope needle is just a diamond inside a tall rectangular block just to the left of the altitude tape. Even after the many ILS approaches Ive flown with the G3X, I still keep looking for a GS pointer next to the HSI.

Configured as an MFD, the moving map can take up the full 7-inch-diagonal screen to provide excellent terrain and airspace detail, instrument charts, plus detailed or overlaid weather (if you have one GDU 375, which has the XM weather/entertainment receiver; the GDU 370 does not, and would normally be chosen as the PFD module). In fact, if you’ve laid hands on a Garmin GPSMAP 695 or 696, you have seen most of the capabilities of the MFD already. Garmin calls each module in the G3X system a line replaceable unit, and the way it manages to make that work is clever. In each wiring shell leading to the components there is a small chip. When you do the initial programming, this chip remembers all the installation parameters, including things like magnetometer calibration, so that if you ever have to replace a component, you can just plug it in and go.

Other manufacturers require you to either totally reconfigure on component replacement, or they give you a means of extracting all the stored setup data to a pen drive or secure-data memory card, which you then insert into the replacement unit. Thats a totally suitable way to approach the matter, but you have to remember to do it first, and it wont help if you have a stone-dead system on your hands. About the only things not to make the transfer are stored data items such as flight plans and logbook contents, and the radio ID of the XM module. If you have to change your GDU 375, plan to call XM to switch your account to the new ID.

Getting Along With One

Sometimes instrument panel design fails to keep up with the instruments themselves, and thats the case with my GlaStar Sportsman. Simply put, the pilots side of the segmented panel is incapable of holding dual GDUs side by side. Thats why my installation has been with a single screen.

To make a single screen work, Garmin has separated the moving map, weather, approach charts and other features that would normally run on the MFD to the lower half of the PFDs screen. At all times, the top half of the PFD is visible. Upshot? The moving map, weather, plates…everything else you want to see besides the basic attitude information is squeezed onto a screen not a lot larger than, say, a GPSMAP 496s. It works, of course, but that sensation of looking at a life-size screen full of useful data that requires little scaling or decluttering to understand is missing. Garmins philosophy is rooted in certified applications where you will always see the attitude information. Its for this reason I strongly recommend you find a way to make a two-screen system fit.

Talk to the Animals

Garmin has made the G3X remarkably flexible in the way it communicates with other systems in the airplane. Three sets of basic serial ports (RS-232) allow the G3X to talk to an SL30 nav/com or an SL40 com radio; this allows frequency channeling for the com side and display of the nav info from the SL30. Initially, the G3X sent flight-plan information to my TruTrak DigiFlight II VSGV autopilot only through an RS-232 output, which means no GPS steering, but just as this is written, beta software came out allowing the G3X to pass GPSS and GPSV steering commands through from a panel-mount GPS-the GPS 400, GNC 420, GNS 430(W), GPS 500 and GNS 530 are currently supported. In time, the G3X is expected to fully connect to an outboard autopilot (see the sidebar Garmins Autopilot Choice, Page 39) to provide other commands like heading and altitude hold, plus climb or descent to preselected altitude. Garmin has not announced whether it will support full approach coupling for analog (ILS, LOC, VOR) approaches, but the current passthrough does allow any autopilot capable of receiving GPSS and GPSV commands through an ARINC 429 data stream to follow the lateral and vertical guidance sent by the panel-mount GPS.

Oh, yes…beta software.

Which brings up an interesting point. Each GDU has its own GPS receiver, but in normal use it does nothing more than inform the moving map. When properly configured, all flight planning comes from the external GPS. It is possible to untether the G3X from the external GPS in the software setup, but then you also lose the ability to display that boxs navigation guidance, such as the ILS course or GPS guidance from the 430W. (Untethering does not affect the connection to an SL30.) I would love to see the ability to use the G3Xs inherently better flight-plan management but also be able to select an external flight-plan source for when you’re flying an actual approach using your IFR-approved GPS. Of course, if you decide you don’t need an IFR-capable GPS, you can rely on the internal WAAS GPS engine and you’ll hardly risk getting lost.

Symbology, Knobology…

While the G3X might lack some of the gee-whiz features such as synthetic vision-a feature that the company has not discounted, by the way-the basic presentation is absolutely top notch. Sometimes its the little things, like the shape of the vertical-speed arrow or the thickness of the magenta line that follows the VSI up or down from zero. The heading and altitude bugs are big and bold. The overall operating logic is quite sound. Having multiple single-function keys along the right side of the display, backed up by five soft keys at the bottom, helps reduce the number of times you push a button or turn a knob to get what you want.

A bit less praise with a single-screen system. For example, if you’re watching the moving map instead of the HSI, which seems almost to be the default option en route, and get a revised altimeter setting, you have to turn the multifunction knob to get to the all-PFD page, then push the BARO soft key at the bottom (removing your hand from the knob), then turn the knob to the new setting, and either wait for the software to auto-dismiss or push either the BARO soft key again or press in on the multifunction knob. Then you turn the multifunction knob to get back to the map screen. Same deal for setting heading or altitude bugs. When you have a two-screen system, its assumed that the PFD will already be on this page, so there is no need to scroll over to it for the change and then back again when you’re done.

The brains of the system are in the GSU 73, roughly 5 inches square, 4 inches high and 3.5 pounds beefy. As it turns out, it can be oriented with the connectors facing forward or back, or even pointing at a wingtip. Pitot-static connections (right) are made at the GSU. All engine monitoring probes will come into this module as well.

The G3X comes with a combined GPS and XM antenna puck. Very clean.

The Future?

Garmin fully expects the G3X to add more features as it matures. The autopilot additions are next, to be followed by the full engine monitoring package. All the company needs to establish is the cost for the sensor pack, which will all be hooked in through the GSU module. (If you’re thinking of having the G3X do your engine monitoring, carefully consider where you’ll put the GSU to reduce the length of the many engine-related wires.) Synthetic vision should not be ruled out, and gaining some form of ADS-B connectivity should be assumed; right now, the G3X will accept TIS traffic data from a GTX 330 transponder (and offers altitude encoding to any serial-capable transponder).

Where the G3X goes in terms of price is hard to say. Currently, a single-screen system (with the GSU box, magnetometer and OAT probe) starts at $9995; add XM to that and its $10,695. A true dual-screen system is $14,995, and any additional display units run $3295. Garmin has not yet set a price on the engine-probe package, but its likely to be around $1000 including fuel flow. Garmins management knows the G3X arrives near the top of this market segment, but is betting that the company’s experience and reputation will carry the day. So far, from a hardware and software standpoint, the G3X has more than met expectations.

One of the screens shared with the GPSMAP 696 is the IFR low-altitude en route chart, shown here in the full MFD mode.

For more information, visit www.garmin.com.

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Marc Cook
Marc Cook is a veteran special-interest journalist who started as a staffer at AOPA Pilot in the late 1980s. Marc has built two airplanes, an Aero Designs Pulsar XP and a Glasair Aviation Sportsman, and now owns a 180-hp, steam-gauge-adjacent GlaStar based in western Oregon. Marc has 5000 hours spread over 200-plus types and four decades of flying.


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