Navcomm Installs: More Than Radios

Whether for backing up a GPS navigator or serving as a primary and one-and-only radio, the digital navcomm radio is far from extinct. It could actually be making a comeback.

That’s because there have been increasing concerns of GPS signal outages, and manufacturers and avionics shops tell us that’s creating more interest in VHF navcomm installations. Honeywell even recently released a new model to replace the popular analog KX155. Last year Trig Avionics brought a fresh digital model to the market and it’s been a brisk seller. 

But regardless of which model you choose, don’t underestimate the wiring and antenna work that can substantially increase the invoice. You’ll also have to deal with CDI compatibility and that could mean spending big bucks on a small EFIS. 

In this article we’ll scan the market for new self-contained navcomms and look at some installation snags that might influence the decision.

DECISION MAKING

As modern avionics upgrades go, a new navcomm upgrade may seem like a simple installation, but it doesn’t always work out that way. For starters, you’ll want to budget every bit of $6000, which for some may be better spent on an IFR GPS navigator install. As we’ve preached in these pages for years, for aging aircraft that haven’t seen a modern avionics upgrade in a while, GPS-based primary IFR navigation adds big capability compared to ground-based VHF nav, both for en route and approach ops.

If your home field (and the places you fly to regularly) have precision RNAV GPS approaches, think about how a modern IFR navigator will change the way you fly compared to your old navcomm. Times have changed so much that Garmin’s current line of GPS-only units (GPS 175, GNC 355 and GNX 375—which supplement the GTN 750/650 line) don’t have VHF nav receivers at all, but are WAAS IFR approach capable. Since this product line came to the market, lots of buyers have ditched the VHF nav receiver entirely in favor of GPS as a primary and one-and-only system.

But the decision to get rid of VOR and ILS capability gets more complicated if you fly lots of hard IFR and even into large airports served by multiple ground-based ILS approaches. It’s a comfort thing.

“I’ve lost, at least temporarily, every GPS in my cockpit because of an airborne signal issue, and for that reason I ended up keeping my old-school King KX155 radio,” one Mooney owner told us recently. He actually went on to spend over $1000 for a bench repair to get it up to snuff.

On the other end of the spectrum, if you have a basic VFR airplane and you have no intentions of ever flying it IFR or even going any distance where a panel GPS would serve the mission, then saving a few grand with a new navcomm to replace an aging one could make better sense. 

Regardless, we think every buyer considering a new navcomm upgrade should also get a quote for a panel GPS with integral comm radio. Garmin’s GNC 355 stands alone in the market as an IFR GPS with built-in comm transceiver (with no VHF nav), and it’s priced at $7695, not counting installation. But that isn’t where the decision-making ends. You still need something to display the VHF nav guidance on and that could mean spending big for a new CDI.

A FEW WORDS ABOUT INDICATORS

A big expense that might tag along with a navcomm upgrade is the nav indicator or CDI, especially when replacing aging radios. There are still plenty of ancient Narco, Collins and King radios begging for upgrade and there’s a good chance that the existing VOR indicator needs replacing, too. 

The mechanical meter movements in vintage King KI209/KI208/KI206, Narco ID825 and Collins IND351 units (to name a few common ones) may have reached the end of life years ago, and they may or may not be compatible with your replacement radio of choice. In that case, it might be time to think about an electronic CDI or even a mini EFIS. 

Garmin’s GI 275 electronic retrofit flight display is a standout for decent compatibility—and perhaps more functionality than you might use. But we like that it accepts both digital and analog nav signals—something that’s important to consider with any navcomm upgrade.

To review, with a form factor that directly replaces most 3 1/8-inch round instruments, the GI 275 is targeted at incremental upgrades. That is, add more of them as budget allows. The GI 275 series are independent multifunction instruments that have TSO and STC certification, a 2.69-inch diameter (active screen size) color capacitive touchscreen and an extremely flexible electrical interface potential. They can function as a primary flight instrument, EHSI, CDI, an MFD with synthetic vision, traffic and terrain display and an engine monitor.

Since the GI 275 CDI version has vertical and lateral VOR/LOC and glideslope and accepts analog navigation signals, it can work with a variety of third-party radios, plus GPS units for a future upgrade. Garmin still makes the budget-based G5, which could be a player in some radio interfaces. 

The G5 DG instrument is equipped for course guidance and ILS approaches with its electronic HSI, but is limited to VHF nav and GPS sources with digital databuses (commonly the Garmin GNS 430W/530W, GTN 650/750 and Avidyne IFD navigators; these output course guidance electronically). The G5 works with Garmin’s discontinued SL30 navcomm and the current GNC 255 digital navcomm through an RS-232 serial bus interface.

Aspen’s EFD1000 Evolution flight displays can accept analog nav inputs when they’re wired through the external ACU, or analog converter unit. This ACU is a standard accessory with the Aspen flagship Evolution display, but optional on the lower-end Evolution models. 

Before buying anything, talk to your shop about what is and what isn’t compatible with your existing interface and how much extra wiring (and accessories) may be needed for it to play in the interface—including with the existing autopilot. The interface potentials—and gotchas—are too much to cover in one article.

GARMIN GNC 255

Priced at $5195, this digital navcomm has been in Garmin’s lineup for nearly 10 years and is often a choice for backing up a Garmin navigator. Maybe the primary unit is a GTN 650 or 750 interfaced with a Garmin EFIS like the GI 275, G3X Touch or G500 TXi. The GNC 255 has decent interface potential with its digital outputs, but it also works as a primary, one-and-only radio for basic panels and offers decent utility.

The localizer and glideslope- equipped GNC 255-series (and comm-only GTR 225) long ago replaced the Garmin-AT SL30 and SL40 line of navcomm equipment, although they aren’t plug- or size-compatible. You might find the SL30 navcomm radio on the used market and the right ones could be worth buying with the right service history and rock-bottom price. They’re space savers with a thin vertical footprint. 

The GNC 255 navcomm is taller, standing 1.65 inches high with an LCD display area that measures 3.46 inches wide and 0.84 inches high. Don’t expect a touchscreen. The Garmin navcomms use traditional buttons and control knobs. In a world where new avionics feature sets are far from simple, you might find that the basic controls on the GNC 255 are simple to use right away because they’re designed exactly the way pilots would expect on a traditional navcomm. 

In fact, the volume controls, squelch control and navigation radio IDENT control layout and functionality is borrowed from the Garmin GNS 430 and 530 navigators. At this point, who can’t operate one of these? Plus, frequency tuning is the same as it ever was—simply dial the frequency on the standby window on the right and transfer it to the active window on the left, using the familiar flip-flop transfer button. 

Also borrowed from the GTNs are the digital nav and comm boards. That means the radio’s nav receiver can work with the popular Garmin GI-106A/B indicators, plus it has compatibility with some BendixKing CDI units—including the popular KI209—when wired for analog composite output. Standard is a 10-watt comm transmitter and there’s an option for a 16-watt transmitter. There’s also 8.33 kHz frequency spacing.

The radio has an internal frequency database of airports and VOR stations. This data is provided for download on the Garmin website and loaded to the unit with a thumb drive. Pressing the Function key enables the menu structure where you can select the database feature to look up the airport name or station ID, much like you would in a GPS. There’s also a reverse lookup feature, which fetches the facility name associated with the frequency that the user manually tunes, using the database and a valid GPS position input. Other features include Morse code station identifier decoding for VOR and localizer stations, an integral two-place intercom, on-screen timers and auxiliary input for music.

TRIG TX56/57

We covered these radios recently (with favorable results) in the September 2022 Aviation Consumer, so we’ll summarize here. Trig sees these navcomms fitting two-seat training aircraft and for backing up Avidyne and Garmin IFR GPS navigators. The $4175 TX56 (for 14- and 28-volt electrical systems) and the TX57 (a 16-watt version for 28-volt systems) trickle down from Trig’s successful and nicely equipped TY96-series comm transceivers, but are equipped with a built-in VHF navigation receiver. Versions with 25-kHz spacing are also available.

Tight on panel space? The Trig radios are slimmer than Garmin’s GNC radio, measuring only 1.3 inches tall. We think Trig did a good job designing the feature set and the bezel controls, which have a durable feel. The installation hardware is equally durable, using D-type connectors. The radio had a built-in intercom and provides voice-activated ICS operation between the pilot and copilot, with auxiliary audio input (and stereo music) to be played over the headphone outputs. 

One of the things that Trig worked hard on—and we commend it—is generous compatibility with legacy and newer navigation indicators. Trig said it understands there are a wide variety of nav indicators to interface with—everything from analog HSIs to electronic flight displays. The TX nav receiver can even work with older King CDIs. That means you can pull out a KX155 radio and not have the expense of sourcing a new indicator. But we say have it bench tested first, to make sure it’s a long-term player. The Trig radio will also work with new Garmin and Dynon EFIS models. 

WRAP IT UP

We think it’s important to bring the aircraft to the shop for an accurate quote for any navcomm upgrade. As simple as a radio install may seem compared to fully integrated big-screen systems, there are plenty of variables that could snowball the job. 

The shop should look closely at the existing wiring, and you should ask if it will use any of it or does it plan on building new harnesses. This includes antenna coaxial cable that could take a lot of disassembly to access and replace. The same applies to antennas. Are the comm and nav antennas in good shape? Don’t shortchange the install by not replacing them if it’s necessary. We’ll look at antennas in a dedicated article. 

Remember, the performance of your new rig will only be as good as the wiring and accessories it’s connected with.