Garmin GMA347: Complex, Feature Rich

Remember when audio panels were just fancy switches? Not anymore. The features are there, but it takes some work to get at them.

by Larry Anglisano

Remember the old days of learning to fly? Enduring pain-threshold noise in a cockpit with an instructor booming commands at the top of his lungs? A hard-to-master skill was just balancing that stupid hand microphone between your knees while awaiting the next radio call.

How could we have been so dumb then? Twenty years later, weve gotten used to headsets and stereo intercoms have become the stan- dard. Two new products that raise the bar in this arena are Garmins new GMA347 and PS Engineerings PMA8000B, both of which make the cockpit more civilized than ever. In this article, we’ll examine the GMA347. we’ll save the PMA8000B for a later review.Garmin GMA347

The $2395 GMA347 was recently inserted into the existing Garmin panel-mount line. Its functionality roots are planted squarely within the G1000 glass cockpit suite and its audio design relates directly to that high-end product.

The successful GMA340 is the older brother and its design traits have been carried into the GMA347, with technology packed into a case similar in design and dimensions to the GMA340, but with different wiring and interface. GMA340 owners shouldnt expect to simply slide a GMA347 into the same tray. It functions without a fair amount of rework.

The unit measures 1.3 inches high by 6.29 inches wide by 7.79 inches deep and weighs roughly 4 pounds, with the interface wiring. Contrast this with the PS Engineering PMA8000B at 1.3 inches high by 6.25 inches wide by 6.8 inches deep and weighing 1.4 pounds.

These days the obvious trick is to make audio panels as shallow and as thin as possible because the radio stack fills up quickly, especially if an MFD is in the offing.

In a busy installation, the audio panel ends up getting pushed to the top of the stack where the potential for chafed wiring exists or for the control panel to get buried under the glareshield in some airplanes.

The control bezel is microprocessor-controlled with LED-illuminated push buttons that are photocell-controlled for auto-dimming. Mode nomenclature is lighted and dimmed via the aircraft radio dimming circuit.

Although the ergonomics are sweet, immediate intuitive operation for the unfamiliar isn’t, in our opinion, based on our experience with a recent first installation and flight test. The GMA347 operating logic, especially in controlling the intercom, works a little differently than the GMA340.Controlling cockpit audio should be a simple and straightforward chore butsometimes isn’t. We know of a new pilot who actually failed a checkride because he stumbled and fumbled with the audio panel (it wasnt a Garmin panel) in busy airspace, missing ATC instructions and showing the examiner that he couldnt handle the workload or the equipment. Bottom line: Youll need to read the GMA347s pilot guide to avoid stumbling. Self-contained in the box is a marker beacon receiver and associated beacon lights sporting functionality that Garmin calls SmartMute technology. After beacon passage, the unit automatically mutes the tone. I t can also drive a remote set of marker lights for redundancy.

Other familiar audio control duties include three transceiver inputs (the third radio could be a marine transceiver or amateur radio for example), five receiver inputs (Navs, DME, ADF), four unswitched inputs that are external audio inputs from remote systems such as autopilot, traffic system, terrain systems and the like.

One of the complaints that many installers have with the original GMA340 is that it lacks enough unswitched inputs and thus isn’t accommodating for applications such as traffic and advanced flight control systems. PS Engineering recognized this need a while back and delivered and now Garmin does, too, with the GMA347.

We wonder, however, when dedicated traffic and terrain audio buttons will surface on audio systems so crews can have actual control over these inputs, rather than hearing them all the time. Passengers squirm in their seats when the robots warn of mid-air and terrain encounters. We need to be able to silence them when appropriate.

Shops have been getting creative in making otherwise unswitched audio sources switched by sending the signal into the often unused COM 3, ADF or DME position that many audio panels have. Pilots can deselect the audio at their convenience to end the distraction. This is extra work at installation and potentially more money out of the owners pocket, but worth it for some.

Microchip Control
PS Engineering developed the squelchless intercom years ago with their IntelliVox and theyve done an impressive job of making it work in the noisy environment of small piston aircraft. Now Garmin joins the party with a similar approach, offering the six-seat intercom in the GMA347 with what Garmin calls MASQ (Master Avionics Squelch), an auto-squelch function with an override into manual squelch mode, so the pilot can regain control of the squelch levels for pilot, crew and passengers when desired. There’s pilot, copilot and crew intercom isolation for added privacy and volume controls for setting pilot, copilot and passenger volume and squelch when in manual squelch mode.

The theory of a microprocessor sampling cockpit voice and noise from each station and then commanding the audio system accordingly is fascinating and in the GMA347, it works as advertised. Our test aircraft was a Beech Sundowner, with a cabin as loud as most piston singles of its vintage. The GMA347 controlled voices with precision, never clipping or missing a vowel.

There were some initial audio volume mismatch issues between audio stations, however, as one pilot plugged in his old David Clark H10-30 while we snobbishly used our Bose X ANRs. We can say that not using a quality set of ANR headsets with either of these new audio systems will shortchange the overall performance.

Messing with the David Clark headset volume controls helped balance the mix, but not entirely. The aircraft owner later reported that the ability to override the auto-squelch is a feature he likes most based on this fine-tuning ability. We also pumped XM Radio tunes from a Garmin GPSMAP396 directly into the GMA347s entertainment input commanded with a remote XM ON/OFF switch described below.

The music would mute as soon as the comm radio came alive and then faded back in when the transmission ended. Music input 2 is designed for passengers and wont mute with radio traffic. Music input 1 is designed for the crew and mutes accordingly.

The common way to pump music into an intercom is to plug a stereo patch cable into the remote mounted mini-jack from the music source. The input can also be hard-wired directly to the intercom. We and the manufacturers caution against possible induced noise from such sources, with ground looping mostly to blame. Noise filters on power inputs help ensure that satellite programming is as clean in your Mooney as it is in your Acura.

Say Again
A major new feature that advances the GMA347s featureset is an integral digital voice/readback recorder that continuously stores the last two-and-one-half minutes of audio. Simply pressing the play button on the right side of the bezel (or optional remote- mounted play button) allows playback. While this may prove handy for students or radio-challenged owners, we doubt it will be a selling feature for the box.

Speaking of remembering things, the GMA347 uses a remote configuration module for storing installation details and customized audio system settings. These settings are configured by the installer using a Windows-based configuration program. The benefit is that any GMA347 unit can be plugged in while retaining original settings. But the configuration process takes additional time as does the wiring for the module itself.

Other features worth mentioning are a dedicated telephone input which allows duplex, private telephone conversations on a satellite phone or standard cell phone while on the ground. A cabin speaker function serves double duty for speaker audio or cabin PA for cabin announcements.

Installation Notes
Weve said this before, but here it is again: Aircraft audio system wiring can be layers deep and its often the wiring that causes grief in a given application, not the audio panel or intercom. Although the equipment can induce its own noise, unshielded audio and other interface wiring serves as a magnet for sucking in all kinds of noisy interference into your headset.

Ignition noise, charging system noise, strobe light noise and pulse equipment interference are all examples of potential noise induction in an otherwise clean audio system.

Wiring harness routing technique is another noise culprit. Unruly power wiring related to onboard systems woven between audio wiring can cause havoc.One look at the harness routing technique in an aircraft will reveal the work of a pro or amateur.

A solid understanding of magnetic induction, RF knowledge, ground loop and frequency theory is required to get this stuff right.

A common corner-cutting technique is to connect a new audio panel to existing wiring to avoid heavy teardown and a complete rewire. In some cases, this might be acceptable if the existing wiring is shielded, tidy and relatively new. It will certainly lower a price quote substantially compared to a rewire, but might yield poor results. Manu-facturers frown on this approach and so do we.

We cant describe the detailed operation of every feature on the GMA327, given its considerable depth. Impressed as we are with it and given the $2395 price, its an excellent value, but a buyer really should look at the PMA8000B before deciding. we’ll do that in a future issue.

In the meantime, the GMA347 is what Garmin says it is: A highly configurable, well-engineered audio system with more inputs than you might ever need. We think any owner would be happy with it. Just realize the installation may cost more than you think.

Contact – Garmin International, 800-800-1020,

Also With This Article
“GMA347 Control Set”
“Custom Audio Control for Music Input”

-Larry Anglisano is Aviation Consumers avionics editor. He works at Exxel Avionics in Hartford, Connecticut.