Garmin gnc

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LPV Approaches and Comm, Priced for Your Aircraft

  • Slim, all-in-one touchscreen GPS navigator and Comm radio for Part 23 Class I/II aircraft (weighing less than 6,000 lbs) and experimental/amateur-built aircraft
  • Take advantage of WAAS GPS navigation with LPV approaches, which offer minimums as low as 200’ to greatly expand your operational capability
  • Built-in 10-watt Comm radio with 25 kHz or optional 8.33 kHz channel spacing (with GNC 355A) plus standby frequency monitoring and automatic frequency identification
  • Pairs with select Garmin flight displays, or integrates directly with your existing course deviation indicator (CDI) for cost-effective installation¹
  • Visualize your entire flight plan, including departures, arrivals, instrument approaches, holding patterns and more on a rich, dynamic global moving map
  • Wirelessly transfer flight plans and stream weather, traffic, GPS position and backup attitude via built-in Connext® technology to the Garmin Pilot™ app and more
Big capabilities come in a small package with the GNC 355 navigator. With its bright, clear high-resolution touchscreen display, you can have the advanced navigation functions you’ve always dreamed of — along with modern Comm radio capabilities. Entering flight information is a cinch, and accessing every function is fast and easy. It’s equally at home in certificated aircraft or an experimental aircraft. And it’s the same 2” height as older navigation equipment and can allow you to keep the composite legacy CDIs already in your aircraft to minimize installation cost¹. That makes GNC 355 the smart, affordable way to add next-generation navigation to your favorite airplane.

Perfect Touch

The moment you power up GNC 355, you’ll see a familiar Garmin homepage on the 4.8” display, which puts the most important functions within only a few touches. Navigate to dedicated pages for the moving map, traffic, terrain, nearest airports, flight plan, procedures, waypoint information, utilities and more. With shortcuts available to the flight plan and Direct-to functions on almost every page, navigation features are usually just a tap away. Use your finger to pan and zoom on any map, traffic and terrain page. Enter waypoint data with the on-screen keyboard. And touch the home button to get you back to the main page at any time.
For added control stability in flight, a shelf across the lower edge of the display serves to steady your hand in smooth and turbulent flight conditions. And if you prefer traditional controls, the concentric knobs provide yet another way to control many of the GNC 355 navigator’s functions.

Intuitive Navigation

With GNC 355, building and modifying flight plans is simple. As you enter waypoints, our FastFind feature automatically begins searching for the nearest identifier as soon as you start typing, so — in most situations — a press or two reveals just what you were thinking. You can also create holds, insert Victor airways and corresponding exit options and add departures, arrivals and instrument approach procedures. Additionally, you can edit your route using the map screen; a handy "rubber band" feature lets you grab any leg of your flight plan route and move it to accommodate a deviation or ATC amendment to your flight plan.

A variety of dynamically drawn and displayed maps provides situational awareness and context to the flight plan by highlighting visual reporting points, navaids, SafeTaxi® diagrams and hazards such as obstacles, power lines and terrain. Plus, the Smart Airspace™ feature automatically highlights airspace close to your current altitude and de-emphasizes airspace away from the current altitude.

Advanced Approach to IFR

The SBAS/WAAS-certified GPS receiver can allow you to fly GPS-guided LPV glidepath instrument approaches down to as low as 200’, greatly expanding your operational capability. You can also access localizer performance (LP) and all area navigation (RNAV) approaches. Precise course deviation and roll steering outputs can be coupled to our GFC™ 500 and GFC 600 autopilots as well as select third-party autopilots so that IFR flight procedures such as holds, NextGen radius-to-fix (RF) legs and missed approaches may be flown automatically. In addition, the GNC 355 navigator lets you create and execute custom holding patterns over an existing waypoint or user-defined waypoint.

Plus, when operating in VFR conditions, GNC 355 can provide advisory vertical approach guidance based on a published glidepath angle or a 3-degree approach glideslope from the runway threshold, while considering terrain and obstacle clearance. With this advisory guidance, you’re able to fly more consistent, precise vertical glidepaths into a variety of airfields.

Powerful Comm Capabilities

GNC 355 offers 10 watts of transmission power with 25 kHz frequency channel spacing or 8.33 kHz channel spacing options (GNC 355A), and it incorporates a number of functions that can save you time and effort. Using the onboard frequency database, airport, weather, center and FSS frequencies are easy to find and can be loaded to standby by simply tapping them from the airport information or flight pages. Recent, nearby and saved frequencies are easy to access, too. And to help you make sure you are talking to the right controller, GNC 355 automatically displays the station’s identifier right below the frequency, e.g., KIXD ASOS or CHICAGO ACC.

With the standby frequency-monitoring feature in GNC 355, you won’t have to worry about missing an ATC call or other critical transmission. The GNC 355 navigator allows you to listen to ATIS without leaving your assigned ATC channel. Swap your active and standby frequencies with a single screen touch. Press and hold the frequency optional remote transfer key to automatically set the emergency frequency as your active radio channel.

Add ADS-B Traffic and Weather

When paired with dual-link Garmin ADS-B solutions, such as our GTX™ 345 series transponder or GDL® 88 universal access transceiver, GNC 355 can display ADS-B traffic targets as well as subscription-free ADS-B weather data in the U.S. Or you can opt for the GNX™ 375 navigator, which offers similar GPS navigation capabilities as GNC 355 but includes a transponder for ADS-B “Out” and “In.” The ADS-B weather link provides in-flight access to animated NEXRAD imagery, METARs, TAFs, winds and temperatures aloft, PIREPs, NOTAMs and more.

When equipped with a compatible ADS-B solution, visual alerts help you recognize and avoid potential conflicts in busy airspace. Our patented TargetTrend™ relative motion technology offers a faster, more intuitive way to judge the direction and closure rate of intruding targets in relation to your aircraft’s position. For example, if traffic is ahead of you and travels along the same track but at a slower rate, the motion vector points opposite of its indicated direction of flight to show you are overtaking the traffic. And, at the start or end of each flight, TerminalTraffic™ technology provides the most comprehensive picture of ADS-B equipped aircraft and ground vehicles in the airport environment. ADS-B equipped aircraft in-flight are easily distinguished from ground vehicles and taxiing aircraft, which are displayed using distinct colors and symbols. All information is presented on a simple, easy-to-understand SafeTaxi diagram with reference to runways, taxiways, hangar locations and more.

Cockpit Integration

The GNC 355 navigator interfaces with Garmin flight displays, including G3X Touch™ (experimental and certified), G5 (experimental and certified), G500/G600, G500 TXi/G600 TXi as well as select third-party displays¹ to provide navigation outputs. It’s also compatible with many older, composite-input based CDIs — allowing you to keep your existing CDI and have an easier, more cost-effective installation¹.

And for even more convenience, you can use the built-in Connext technology to stream information between GNC 355 and compatible Garmin portables and mobile devices running the Garmin Pilot or FltPlan Go apps. You can create flight plans at home and upload them at the airport. And you can stream GPS data, backup attitude information (from the built-in AHRS) as well as traffic and weather to your mobile device or Garmin portable, making them even more useful cockpit companions.²

Plus, our optional Flight Stream 510 installs in the memory card slot of GNC 355 to enable our Database Concierge database transfer and management capabilities via our Connext gateway. At home, you can download selected databases onto your mobile device by using the Garmin Pilot app. Then, once you get to the airport, Flight Stream 510 will automatically establish a wireless connection to the Garmin Pilot app and upload the databases from your device to your GNC 355 in minutes.


    Physical and Performance

  • TSO applicability: C128a; 2C128; C146e Class 3; C157b Category 1; C165a; C169a Class C, E, 4, 6; 2C169a Class C, E, H1, H2, 4, 6; C195b Category B1, B3, B5, B7
  • Display size: 4.8" (122.5 mm) diagonal
  • Display resolution: 732 pixels (W) x 240 pixels (H)
  • Unit bezel height: 2.02" (51.0 mm)
  • Unit bezel width: 6.25" (159.0 mm)
  • Unit depth with connectors: 11.23" (285 mm) (measured from face of aircraft panel to rear of connector backshells)
  • Unit weight: 3.3 lbs (0.6 kg)
  • Maximum altitude: 35,000 ft
  • Input voltage range: 9 VDC - 33 VDC
  • Maximum display brightness: 260 fL
  • Operating temperature range: -20° C to 55° C (-4° F to 131° F)
  • Bluetooth version: 4.2
  • Number of GPS channels: 15 (12 GPS and 3 GPS/WAAS/SBAS)
  • LAT/LON position accuracy:


I replaced my old Terra units on my 182 Skylane with the GNC355 to avail the benefits of a COM radio and GPS that drives my CDI KI209. Pros: - Very ergonomic/ Sized to fit your existing set up - Touch screen is a charm!! - Screen size is good and provides good visibility - COM usage is a breeze... Easy to switch between frequencies - GPS works great, no issues, dot on.. - Provides a lot of features that you can change with your touch screen Cons: - Updates are expensive, you may have to go for a yearly option, but still high on price based on what package you choose. Overall a good combination for someone who needs a GPS and COM in one unit.

Mahesh I

September 13, 2020

I installed one in my experimental. It works well and is connected to dual G5s. However, if you want a vertical deviation indicator on a G5 you must also connect to a GAD 29. The 355s ARINC 429 signals go through the GAD 29 and provide the VDI to the G5. Previously, I had an AERA 660 connected to the G5s and it provided a VDI through an RS 232 signal. Only another $475 for the GAD 29 and another $50 for the GAD 29 connector kit.

Fred S

April 9, 2020


Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: How many RS232 Tx/Rx pairs and how many ARINC 429 tx/rx pairs does the GNC 355 have? Can the GNC 355 be connected to 2.25 mid continent cdi such as MD222-506 or MD222-406 ?

This has 3 RS232 ports and 2 ARINC ports. Per the manual you can connect to the MD222-406, but the MD222-506 is not listed.

Q: Hi I am interested in the Garmin GNC 355, I want to use it with an S Tec 50 AP and a Garmin G5. To use GPSS do I need the GAD 29 B or is the roll steering included in the GNC 355 Regards Frank

Per the installation manual, you can connect this directly to your autopilot.

Q: Can the Garmin GNC 355 be connected to the Dynon Skyview Classics CDI?

Per the manufacturer, no they will not work together.

Q: Are the GNC 355, GPS 175, or the GNX 375 ILS or localizer capable?

No, these unit are for GPS approaches only. No ILS, LOC or VOR approaches.

Q: Can the Garmin GNC 355 be tuned to the 3rd decimal?

Yes, P/N 11-17439 can be tuned to 8.33 kHz.

Q: What is the circuit breaker size for the GNC 355?

The circuit breaker size is 5 Amp 28V.

Q: Does the GNC 355 include the GPS Antenna?

Yes, This will include the GA 35 GPS antenna.

Q: After purchasing the GNC 355, how are we given access to the installation instructions without being a Garmin dealer? I assume you will be providing it or some way to down load them.

Please contact our avionics sales team after you receive the unit and we can send the install instructions PDF. We can send all manuals digitally at that time.

Q: Will the GNC 355 display traffic or weather from another Garmin device via connext or will it only display traffic/weather from a GTC 375/GDL88?

Yes, it will display traffic from the GTX 345.

Q: Will the Garmin GNC 355 built-in Connext technology allow bluetooth connection to ForeFlight?

No, at this time, the unit will not allow Bluetooth to connect to Foreflight. Garmin Pilot and FlghtPlan Go are the only compatible apps.

Q: Will the GNC 355 connect with an MX-20?

Yes , Per the installation manual the GNC 355 will connect with the MX-20.

Q: Can a Stratus 3i be a source of weather and traffic for the Garmin GNC 355

No, the Stratus 3i is intended to communicate only with an EFB on your tablet.

Q: Who provides updates to nav data?

You can find the nav data updates at

Q: Does the GNC355 come with an STC in the package? or how exactly is this compliant with the FAA after installation on a certified airplane?

In the box, the manufacturer includes an STC redemption code that will give access to downloading the document.

Q: Does this unit come with a harness?

No, the GNC 355 part # 11-17439 comes with the unit, registration card, and GA 35 antenna in the box.

Q: Does this Garmin GNC 355 unit include the mounting rack, install kit, and back plate?

Yes those items are included.

Q: Are the G5 and the GNC 355 compatible? If so, what components are required?

Yes, the G5 and the GNC355 will communicate with each other and you will require the GAD29B for complete connection.

Q: Would this Garmin GNC 355 be compatible with a Narco ID-825 CDI?

No, per the manufacturer installation manual the Narco ID-825 CDI is not compatible witht he GNC 355.

Q: Does the GNC355 provide GPSS and/or GPSV signaling on the ARINC429... for autopilot control?

This unit is only compatible with select autopilots, however, it offers GPSS signal where necessary.

Q: Can or does the G5 share the GPS antenna reception signal (thru Can bus or RS232?) from the GNC 355 when one antenna is utilized and plugged into the GNC 355?

They best way would be to have the WAAS GPS antenna on the GNC355 and allow that unit to be the GPS source for the G5.

Q: Can I use the GNC 355 without an audio panel? If so, there are no wiring instructions in the installation manual.

Per the installation manual the GNC 355 needs to be installed in an audio panel. Installation manual Rev 3 has the wiring instructions starting on page 99.

Q: Can the GNC 355 receive position data from my GTX345? Thank you.

The GNC is a GPS unit. It will require its own antenna. The GTX 345 can share that signal as well as provide ADS-B IN.

Q: Will this Garmin GNC 355 work with Garmin 275 HSI?

Yes, the Garmin 275 HSI is compatible with the GNC 355.

Q: Is the Nav/Com Output of the GNC 355 compatible with my legacy PS Engineering PMA 8000B Audio Panel?

Yes, you can connect the GNC unit to your audio panel for audible alerts.

Q: Does the Garmin GNC 355 come with a GA35 antenna?

Yes, This will include the GA 35 GPS antenna.

Q: Can the GNC 355 control a remote transponder?

Per the manufacturer manual it does not list remote transponders as compatible.

Q: I have two G5s a STEC-30 and a 530W. can I retain the 530W as a backup GPS using common antenna?

No, each unit will require its own antenna.

Q: Im thinking of buying GNC 355 and Garmin GI 106B... Do I need to buy additional cables/connectors for them to work together?

It is for anti-rotation.

Q: Im thinking of buying GNC 355 and Garmin GI 106B... Do I need to buy additional cables/connectors for them to work together?

These come with the connector kits that are required to create a wiring harness. You will need to purchase coax cable and wire separately.

Q: I have a GTX 335 (out) and a GDL 50R (in) installed for ADS-B operation. Is the GNC 355 compatible with the GDL 50R ADS-B tsource o display the in notifications? Using Bluetooth or by cable connection?

The GNC355 is not compatible with the GDL50R per the manufacturer.

Q: Will the GNC 355 work with dual G5s and GFC 500 autopilot?

Yes, the GNC355 will interface with those units.

Q: Can this GNC 355 is applicable for Pacific (Philippines)? What are included in the package?

The GNC 355 is pre installed with the Americas database. This can be modified and uploaded via after you receive the unit. In the box: IN THE BOX: 010-02232-02 unit + 010-02328-00 registration card + 013-00235-00 ga 35 antenna



Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: Which CDI indicators will works with the GNC NAV/COM?

For a new glideslope and LOC/VOR CDI receiver the GI 106A is the first recommendation under part number 11-05768.

Q: Will the GTR & GNC units operate without purchasing and maintaining a current database subscription from Garmin?

Yes, the database is an optional feature on the GTR & GNC series.

Q: Will these radios integrate with the Dynon 180 like the SL 30 model does?

Yes, the GNC series will still output the NAV like the older SL 30 units.

Q: Is the a wiring like with the 430W units to a Sandel 3308?

Yes the Garmin GNC Nav/Com has a 429 Arinc output which can go to the Sandel.

Q: What size circuit breaker does the GNC 255A 10W version require? What is the maximum current draw?

For the Com side 5A @ 28V & 10A 14V and for the Nav side 2A @ 28V & 4A @ 14V. The amp draw varies based on the Com and Nav as well as 14 and 24 volt systems. Always refer to the manual before installation.

Q: What antennas are recommended for the GNC 255A Nav/Com radio? Is there a wing tip antenna that can be used for this radio?

There is no recommended antenna for any radio as almost any Com and Nav antenna can be used. They are built for different speed ratings, mounting locations and some are certified (TSO'd) and some are for experimental aircraft only. Type antennas in the search box on Aircraft Spruce website for our product selection. Archer and Advanced composite are two wing tip types but both are not certified (TSO'd) as they are intended for experimental aircraft only.

Q: Does the integrated intercom offer an auxiliary audio input (for something like an MP3 player)?

No, it is a basic intercom, for a stereo option or 3.5mm input you will need to go with an external intercom.

Q: What voltage do these units operate on?

It can operate on a 14 or 28 volt system.

Q: Is it possible to purchase the installation tray and wiring harness separately from the GNC 255A NAV/COM unit?

It is possible but we will have to special order this for you and may not cost or have the same lead-time as Garmin does not stock it this way. Please call us and we can get pricing and lead-times.

Q: Does the GNC 255A provide the same radial display of the standby VOR like the SL 30? With the primary VOR/LOC frequency providing guidance to your HSI or CDI, the standby frequency can be tuned to a second VOR to display the current radial on which your aircraft is flying.

In speaking with Garmin, the GNC 255 does not have the standby VOR like the SL 30.

Q: Is the unit compatible with my existing KI-209 GS/Loc CDI?

Per the manufacturer: Yes all Garmin GNC 255's are compatible with the King KI-209.

Q: What does the wiring harness include for the Garmin VHF NAV / COM GNC 255A / B? Does it include the harness to interface with the indicator head?

No, the stock harness (11-11354 or 11-11355) does not include connections to the CDI. Please see part 11-13040 or 11-13041 for the custom harness which includes CDI connections.

Q: Does the GNC 255A interface with portable GPS Garmin 695/696?

Yes, you will need the power/data cable part number 11-07056.

Q: Is the GNC 255a or 255B a direct replacement for the SL30 without harness modification

No, the upgrade to a GNC will require a new install of rack, connector and harness.

Q: I have a GNS430 (non waas) approx. 5 years old. Does the Garmin GNC255 nav / com interface with the 430?

The 430 is a GPS NAV/COM. The GNC 255 is a NAV/COM. There is no need for any of these two units to tie together. They can both tie to an audio panel to provide a dual NAV/COM system.

Q: Is the unit compatible with my existing KI-206 VOR/ILS indicator?

Yes, per the Garmin install manual, the KI 206 will work with the GNC 255A.

Q: Can the Garmin GNC255 interface with an Aera 560 portable GPS?

Yes, you will just need the Garmin Aera 500 series power data cable.

Q: The description of the Garmin GNC 255A / 255B says it can find the nearest airport, etc. To do this, must it have a GPS signal coming in?

Yes an approved Garmin GPS signal must be wired to the GNC unit.

Q: Will this Garmin VHF NAV / COM radio 255A / 255B unit interface with the G5? Will it send navigation information to the G5?

Yes, this can interface with the experimental G5 and the G5 DG/HSI for certificated aircraft.

Q: Can I install this Garmin GNC 255A / 255B on Cessna 150?

Yes, this is a TSO product, however, we can only sell it to experimental install customers. For certified install, you will need to purchase the unit from your local Garmin install shop.

Q: Does this GNC 255A interface with Garmin Aera 796 GPS ?

Yes, the GNC 255A can interface with the Aera 796 via a bare wire power data cable.

Q: Does Garmin make a nav/com radio for certified aircraft without having to buy a gtn-650?

Yes, they do. The model: GNC 255 P/N: 11-11348

Q: What kind of certificate comes with GNC 255A NAV/COM?

We can provide manufacturer certificate of conformance or 8130 forms, please request them at the time of order. Additional charges may apply.

Q: Can this Garmin VHF NAV / COM GNC 255A / 255A be paired with my Garmin 796? Is it TSO for CESSNA 182P?

Per the manual, using the bare wire kit p/n:11-10044 you can connect to it for frequency data. A TSO is a standard certification not specific to any aircraft, please speak with your Garmin approved installer for more information. Also please be aware that we cannot sell this unit for certified aircraft.

Q: Do you sell this item TSO with a FORM8130-3 for a Certified aircraft?

No, we can sell these units only for experimental aircraft installation.

Q: Can you sell the certified version of this Garmin GNC 255?

No, we can only sell this unit for experimental aircraft installations.

Q: Will this interface with my existing King KCS 55A HSI system?

No. That unit is not on the approved list of compatible units.

Q: Can I switch between a GNC 355 and a GNC 255 for nav indications on a G-5?

Yes. The G5 can connect to both the GNC355 for GPS information and GNC255 for VOR/LOC and glideslope. You need a GAD29.

Q: Will this interface with an Avidyne IFD540?

The manual does not make any reference to the Avidyne products. We cannot confirm these can be interfaced.

Q: Does the UNIT only means only the radio is in the box and no plugs tray included?

"unit only" means there is no wiring harness included. However you will still get the tray and connector kit.

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When Garmin introduced the GPS 175 (and ADS-B transponder-equipped GNX 375) budget IFR navigator earlier this year, we wondered why it didn’t have a comm radio. Then a couple months later, Garmin tossed the $6995 GNC 355 in the mix with, you guessed it, a built-in comm.

That leaves no fewer than a half-dozen choices for new GPS navigators, counting ones from Avidyne and not counting some worthy used-market choices. In this article, which is part of our Avionics Bootcamp series, we’ll attempt to sort out the buying decision so you’re better prepared to round up some quotes for installation.

To do that, let’s look at three real-world upgrade scenarios and what we think are the best possible solutions, mostly from an interface standpoint. You’ll have to answer for yourself how you might fly with the tech once it’s in.

For starters, ask yourself if you can fly without a ground-based VHF nav, including raw-data ILS. You’ll see why.

Navigator Rewind: Garmin Gnc

It was around 1996 or thereabouts when Garmin started cranking out the GNC 300XL. This was a TSO C129(A1) IFR approach GPS navigator and as a bonus, it had a utilitarian moving map (of course, any panel map back then was utilitarian) and a built-in VHF comm radio. It had no VHF nav-strictly GPS. The GNC series was a clever idea and almost the perfect solution for backing up a traditional navcomm, or for more basic panels, it worked as the primary rig because of the built-in comm. The cheaper GNC 250XL had a VFR GPS and a simpler install. The GNC series sold like rush-hour coffee at Starbucks.

Garmin killed the line some years back, and now brings it back with the GNC 355. We wrote about the first products-the ADS-B equipped GNX 175 and entry-level GPS 175-in the May 2019 Aviation Consumer.

Like the 175 and 375, the new comm-equipped GNC 355 has a 2-inch-high bezel, which helps differentiate itself from the larger GTN 650 navigator, nor does it have a VHF nav receiver.

Like the other two budget units, the idea with the GNC 355 is to replace aging navigators without having to do much if any stack rework. Maybe there’s an old Apollo GX60, King KLN89B or even a King KX155. The GNC should easily fit in without restacking.

21 GNC355_(5) COM Standby

Like the other two units in the series, the GNC 355 is designed to work with a variety of third-party nav indicators. Remember, these boxes are WAAS equipped for full IFR GPS approach capability, so you still need an indicator to display course information. The new series has Garmin’s Connext wireless interface for traffic, weather and flight plan streaming to and from a tablet.

There’s a long list of compatible indicators-everything from Garmin’s own GI 106A/B to the King KI209 and KI525A HSI-even old Narco and Collins indicators. But we suggest asking your shop if these indicators are healthy enough to retain for reliable service. Some are not. The unit will also work with new stuff-including Garmin and Dynon EFIS.

The new touchscreen mapcomm is intended for Class I/II aircraft that weigh 6000 pounds or less, and can be installed under a 700-aircraft blanket AML-STC.

Let’s look at a couple of navigator upgrade strategies. These examples are aircraft owned by actual readers who we recently helped noodle the upgrade decision.

Piper Cherokee

26 GNS430W

If you own something like the Piper Cherokee panel shown below, it’s begging for an upgrade. The first thing we would do is remove the King KR86 ADF system that’s at the top of the right stack. At the same time, get rid of its antennas and reap the benefits of a cleaner airframe. Below it in the stack is a King KLN90B approach GPS that’s installed for VFR. Out with it. A CRT display failure makes it a boat anchor.

This aircraft has already been upgraded with a uAvionix skyBeacon, so it’s ready for the 2020 mandate. But it has an old tube-powered transponder that won’t last much longer.

With dual KX170B navcomms, this panel is the poster child for Garmin’s new GNC 355 mapcomm. You could even retain the second KX170B as a backup radio and install the GNC 355 as the primary. It’ll work well for instrument training and make for an efficient radio stack. Since the glideslope receiver is built into the primary KI214 nav indicator, you could drop it down and use it as the secondary system-if it works. We say yank it out and save some weight. The KI214 retired long ago.

At the end of the day, this will be a $10,000 upgrade, but with a new transponder (maybe Garmin’s GTX 327 Mode C unit) and the antennas and other cleanup work, plan on $14,000. If you want to ditch the KMA20 audio panel for something newer and more capable, you’re well north of $16,000.

Cessna 182N

22 GNX375_0487_HOME

This late 1980s panel has a non-WAAS Garmin GNS 430 with Garmin GI 106A indicator, plus a KX155 with KI208 indicator as the secondary system. The aircraft has a Garmin GTX 327 transponder and it needs ADS-B. The goal here is to jump into the world of WAAS approach capability and out of the aging GNS 430. The airplane has an S-TEC 50 two-axis autopilot with nav tracking and also a GPSS steering system.

One relatively easy upgrade for this panel is Avidyne’s IFD440. It can slide into the GNS 430 wiring and work just fine with the Garmin indicator and with the S-TEC autopilot. But since the IFD440 is a WAAS unit, it won’t work with the existing Garmin GPS antenna and cabling. The shop will need to remove the headliner, change the cable and install the WAAS antenna.

Avidyne’s IFD440 retails for $11,999 and you might get a trade-in of around $2000 for the non-WAAS GNS 430 that comes out.

Another option for this panel is Garmin’s GNX 375, which will solve the ADS-B dilemma and add LPV approach capability. But unlike the Avidyne IFD440, it doesn’t have a comm radio and it doesn’t have a nav receiver. That means you’re relying on a single comm radio (with the KX155) and going without ILS capability. Decisions, decisions.

Beech Skipper

25 IFD440 Arrow Left facing

You just bought a little Skipper for knocking around the local area, but you want to start doing some instrument training. It’s not going to happen in this airplane with the single Narco navcomm radio with a nav indicator labeled “Inop.” The previous owner spent some money on new gyros and installed a Garmin GTX 327 transponder and a new altitude encoder, but no ADS-B.

For this we think Garmin’s new GNC 355 is the right solution. It will bring a reliable comm radio and of course the utility of an IFR GPS so you can get started on your training. The fly in the ointment is that old Narco VOA-series indicator that needs to be replaced. Maybe your shop has a used King KI209 (around $900 for a good one), or spring for a new Garmin indicator for $2350. Price a G5.

As for ADS-B, this is the perfect application for the uAvionix skyBeacon. When the dust settles, plan on a $12,000 upgrade.

Not a Slam Dunk

23 IFD440 with syn vis

We can’t come close to covering all of the panel combinations, so if you have one you’re struggling with drop us a line and we’ll take a look.

We can say that while Garmin’s new line of budget navigators can be a dollar saver (the GNC 355 mapcomm is $5000 less than a GTN 650), it also muddies the buying decision. For example, a lot of panels need a new comm radio, transponder, GPS and ADS-B, but the GTX 375 falls short for these applications for not having a comm. The new GNC 355 does, but it doesn’t have the ADS-B transponder. That leaves a hole in the line filled by the higher-priced GTN 650, of course. We asked Garmin why it didn’t include the ADS-B transponder in the comm-equipped GNC 355 and it said the transponder simply wouldn’t fit in the chassis.

This aside, there are still a lot of panels equipped with the older Garmin mapcomms and in our view the new GNC 355 is hands-down the best option for replacing them. Unfortunately, the unit (and the others in the series) isn’t pin-for-pin compatible with the old wiring. The boxes are too different, says Garmin.

But from a panel real estate standpoint, the units will drop in place of many older GPS units (or navcomms) with minimal amounts of stack rework. That means a quicker install. As for space behind the panel, the entry-level GPS 175 is the most efficient. It’s only 6.58 inches deep, which follows the design of the original GNC 250 from years ago.

24 Warrior 170Bs

The other thing we like about this new line is Garmin made the units compatible with a ton of older analog autopilots-everything from a basic Cessna 200A to S-TEC 60-2. If you are considering a budget EFIS upgrade at the same time, they’ll work with Aspen’s VFR display, and of course Garmin’s own G5 EFIS.

What makes the buying decision real muddy is that none of these budget navigators have ILS receivers and only you can decide if you’re comfortable doing without, based on where and how you operate the aircraft. At 4.8 inches diagonally, the display is small, but the savior is the wireless interface for tablets running the Garmin Pilot or ForeFlight apps.

For higher-end rides-we’re talking twins and go-places complex pistons-full-up navigators like the Garmin GTN and Avidyne IFD will be the boxes of choice for ILS capability. But for basic panels begging for a modern upgrade that won’t break the bank, we favor Garmin’s generously equipped GNC 355.

Larry Anglisano

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. When he’s not writing, Larry is working on a collection of guitar compositions for the upcoming Flying n’ Jazz production.

MODULE-15 Part 1:Garmin GNC 300XL GPS Overview and Communications ( Also 150XL, 155XL, 250XL )


Gnc garmin


GPS 175 and GNC 355 GPS Navigators Familiarization


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