Garmin G5 DG/EHSI: Low Cost, STC Limited

Garmins G5 electronic directional gyro/EHSI doesnt have autopilot interface yet, but it will likely play an integral role in new low-cost autopilot interfaces.

As a follow-on product to the STC’d G5 electronic attitude indicator, Garmin’s G5 electronic directional indicator is taking sizable criticism because the instrument doesn’t interface with autopilots. While Garmin says this is a temporary limitation, it’s easy to understand the backlash.

After all, the G5 EHSI is intended to replace mechanical, vacuum-driven DGs—many of which work with the heading channel on a variety of existing autopilots. But looking to the future—as in the coming months—there’s a bigger story here.

As TruTrak and Trio move closer to earning STC approval for experimental autopilots, Garmin’s standalone G5 series instruments seem perfectly positioned to play with them. Here’s why, plus an overview of the G5 heading indicator.

Choose One or Both

G5 EHSI display

From a technical standpoint, the main thing that differentiates the $2449 G5 heading indicator from the $2195 G5 attitude indicator is a remote heading sensor. The instrument, which was born in Garmin’s experimental line, is certified via an approved model list (AML) STC for close to 600 aircraft makes and models.

The G5 DG/EHSI and the G5 attitude instrument share the same chassis (3.4 inches wide and 3.6 inches high), the same 3.5-inch QVGA LCD color display and both have a four-hour lithium-ion backup battery.

When the two instruments are installed as a pair, the secondary G5 (as a directional instrument) can also be used as a reversionary attitude display because it has an independent ADAHRS.

Garmin said that when the G5 attitude instrument is installed in the primary attitude position, it can’t revert to a full-up heading display (the STC doesn’t allow it), although it can display the current heading in a data field at the top of the screen.

For magnetic heading resolution, the G5 requires the $275 GMU 11 magnetometer—a remote heading sensor that can connect with two G5 displays. The magnetometer, which uses a similar housing as Garmin’s Flight Stream 110/210, is mounted inside the airframe in an interference-free location.

You don’t have to use the G5 directional indicator as a navigation display (EHSI), but if you do, it requires the GAD 29 navigation data interface module (which bumps the price to $2975, including the magnetometer and backup battery), plus a Garmin navigator or navcomm.

Compatible GPS navigators include the current GTN750 and 650, legacy and WAAS GNS navigators and the GNS480. Navcomms include the GNC255 and discontinued SL30. The GNC255 and SL30 interface don’t require the GAD 29 nav adapter as these radios communicate directly with the display over a CAN bus.

Without a nav or GPS interface, think of the G5 simply as a digital directional gyro with heading reminder, plus there is a data field at the top of the display showing current heading. With battery-equipped dual G5s, you can remove the vacuum system.

As an EHSI, the G5 is approved as a primary source for displaying vertical and lateral GPS/VOR/LOC course deviation, plus it shows groundspeed and the distance to the next waypoint. Since the G5 is approved for both VFR and IFR, it can be used as the one and only indicator for Garmin’s navcomm radios and IFR navigators.

The G5 directional indicator’s feature set couldn’t get easier. You adjust the onscreen course pointer with a rotary bezel knob that serves double duty as a heading bug. There’s a Micro SD port and a power key on the lower bezel.

Limited By The STC

G5 Dual Panel Display

If you’re wondering why the G5 doesn’t work with autopilots, don’t think for a second that Garmin doesn’t have the engineering expertise to make it happen. The company’s retrofit G500/600 PFD has been installed with almost every certified GA autopilot, plus the G5 currently works with the G3X experimental autopilot. While there are some technical challenges in interfacing with old analog autopilots, that’s hardly the issue.

Recall that it was Dynon and EAA that pioneered the first AML-STC for an experimental attitude instrument (the Dynon D10A) last year. Although the certification of an experimental EFIS for Part 23 aircraft was huge progress, the FAA’s regulatory compromise was to prohibit any interfacing with autopilots—or even with navigation systems.

G5 lithium ion battery

Just months after the Dynon/EAA STC, the FAA issued Garmin an STC (but with a much broader AML) for its scaled-back version of the experimental, non-TSO’d G5, while ordering the same limitations it did for the Dynon D10A. That meant no autopilot or navigation interfacing—a limitation that remains in place even with the latest approval for adding heading and nav functions. To get more background, we went right to the source.

Robert Murray at Garmin’s aircraft certification division made it clear that while the FAA’s Small Aircraft Directorate has been a huge proponent of new safety-enhancing equipment (these recent instrument STCs are proof), it’s proceeding with caution. Worth mentioning is that approval is being done using ASTM function verification standards, not traditional DO-178 software standards, which is a far more costly certification process. The tradeoff is baby steps when it comes to more advanced functions, including interaction with autopilots.

GMU 11 magnetometer

“In expanding the G5, we’re currently laying out our safety case with the FAA, proving that a basic autopilot interface doesn’t induce hazards when controlling the aircraft,” Murray told us. This functionality doesn’t include driving the autopilot with the G5’s ADAHRS-derived pitch and roll guidance, but instead providing basic heading command and potentially, nav/GPS course tracking.

The bottom line is that gaining autopilot approval will require a change to the autopilot-forbidding policy used for the original G5 (and Dynon D10A) AML-STC. As it stands now and as Murray put it, “We think we can satisfy the FAA with our current G5 architecture such that they’ll adjust the policy in our favor.”

A Larger Role

Moving forward, we see Garmin’s budget-priced G5 flight instruments eventually playing a sizable role in the market of STC’d experimental autopilots, including interfaces with TruTrak and Trio systems. For one thing, a pair of G5’s connected to the autopilot can provide sizable amounts of redundancy because they offer independent ADAHRS and crosscheck—something the FAA will likely require under ASTM approval.

Last, we fully expect to see Garmin move aggressively with a wide-reaching STC for its existing experimental autopilot, with the G5 attitude and directional instruments front and center in the interface.

Click here to see a video about the Garmin G5!

Editor in Chief Larry Anglisano has been a staple at Aviation Consumer since 1995. An active land, sea and glider pilot, Larry has over 30 years’ experience as an avionics repairman and flight test pilot. He’s the editorial director overseeing sister publications Aviation Safety magazine, IFR magazine and is a regular contributor to KITPLANES magazine with his Avionics Bootcamp column.