Garmin VHF Nav / COM Radio GNC 255A / 255B For Certified Aircraft

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GNC 255A 10WGNC 255B 16W


New series of VHF NAV/COM radios, the GTR and GNC series. As the replacement products for the popular SL30 and SL40 models, the GTR series COM transceivers and GNC series NAV/COM radios include a breadth of new features to reduce pilot workload, while also offering an affordable solution to meet the requirements of the 8.33 kHz channel spacing mandate recently enacted by the European Union under the Single European Sky (SES) initiative.

These products have truly reinvented the stand-alone aviation COM radio with novel features like reverse database look-up and the COM monitor function, which bring new efficiencies to cockpit radio management. Beyond that, these products demonstrate Garminís commitment to aviators worldwide, providing the solutions they need to meet the latest regulatory requirements in their regions, such as the recent SES mandate.

The SES mandate
The SES mandate aims to enhance safety and efficiency of air transport in Europe by tripling the number of channels available for aircraft communications. This mandate requires all European aircraft using European airspace to be equipped with 8.33 kHz radios by December 31, 2017. Select GTR and GNC models offer both 25 kHz and the 8.33 kHz operational capabilities required to comply with the law.

The GNC series NAV/COM
The GNC series NAV/COM radios offer all of the same COM features, while also adding navigation capability with VOR/ILS with Glideslope. The GNC series works well with select Garmin flight displays including the G500, G600, G500H and G3X to display the NAV indicators in the primary field of view, and can integrate with most autopilots.

The GTR and GNC series are more powerful than their SL-series predecessors with versions available with 10- or 16-watt transmit power. The GTR 225 includes 10 watts of transmit power and 25 kHz frequency spacing.

All products in the series have received the Federal Aviation Administrationís (FAA) Technical Standard Order (TSO) authorization.

Night Vision Model
Night Vision Goggle (NVG) capable COM and NAV radios. The GNC NAV/COM and GTR COM series of radios are now even better with the addition of new, NVG capable versions.

This latest edition grows our list of NVG capable products which already includes NVG specific GTN series navigators as well as G500/G600/G500H flight displays.
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  • The series offers a variety of original features never seen before in a stand-alone COM radio. A unique frequency database makes it easy to find all the frequencies associated with a given airport or facility just by entering the location name or station ID. And when manually tuning a frequency, the reverse lookup function will automatically provide the navaid and/or airport identifier. Pilots can also find the nearest airport, area control center, flight service station, weather frequencies and VORs. All models also include a COM monitor function, which provides the utility of two receivers in one, allowing the pilot to listen to transmissions like ATIS without leaving the active ATC frequency, as one example.
  • The GTR and GNC series automatically store the 20 most recently called frequencies. Plus, the radios allow for storage of up to 15 favorite frequencies such as the pilotís home airport or other frequently visited destinations. A familiar flip-flop feature allows channels to be entered in a standby window, and then activated with a press of a button. All models also include a built-in, voice activated two-place intercom making it a great solution for a two seat aircraft without an audio panel. A built-in timer can assist with approaches, holds and other assigned maneuvers.


  • GNC 255A: COM, NAV, 10 Watts, 8.33kHz
  • GNC 255B: COM, NAV, 16 Watts, 8.33kHz
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I had to repair or replace and I’m glad I replaced an old Narco with this, the features this little box has is amazing. Hard to believe what all it can do and it’s just a nav comm

Brad S Verified Purchase


November 15, 2023

We have had this installed (GNC 255 A) paired with a KI-204 indicator and PS Engineering PMA 8000-BT audio panel utilizing the Approach FastStack connecting system (which allows an A&P to install (as long as an IA signs off on the paperwork) on our 1958 Cessna-172.. It is by far the best navcom we’ve had in this airplane, crisp,clear,long range, easy to learn the basics and most of the features. Everyone who flies with us compliments us on the combination (especially if they make or receive a phone call through the PMA 8000-BT), or when they make some ILS approaches, use the comm over long distances (100 miles or sometimes longer). The GNC 255A was a purchase we would purchase again without any hesitation whatsoever.

Lloyd M
January 25, 2023

This unit (GNC255B) was installed with a Dynon HDX and a GPS175, the installation was relatively easy and Dynon had instructions for the interface wiring for both units, (although you will need to hunt Dynon paperwork for those instructions. . . the set up procedure was good. . . if you are computer savvy

June 4, 2021


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: Can A&P install the GNC255 series in certified aircraft? And, is the STC and installation manual available?

Yes, an A&P can perform the installation. The unit does not have an STC, however it does carry a TSO certification

Q: Is this product compatible with the Dynon HDX system?

Per the manufacturer, yes it will communicate with the Skyview system.

Q: Is a 337 form required or can an A&P install this TSO product without 337 form as minor alteration?

We always recommend to consult with your A&P and / or IA to ensure all proper paperwork is filed.

Q: Is glideslope included on the Garmin GNC 255A / 255B?

Yes, this is capable of receiving the GS signal.

Q: The text says that the unit will interface with the G500, G600, G500H and G3X displays. Will it interface with the G5 displays and the Garmin 5xx autopilot?

Yes, the GNC255 will communicate with the G5.

Q: Will this unit drive a KING VOR head with glide scope?

Per the manual: VOR OBI output provides bearing information from the currently tuned VOR station for Bendix/King Serial OBI devices based upon the VOR receiver. When a localizer channel is tuned on the VOR/LOC window, there is a bit in the data stream set to indicate that a localizer frequency is tuned which stows the needle or drives it to the three oclock position.

Q: I have the old cessna raido KX155 in my 152 and is a 28V system witch one would i need 10W or 16W ?

Either model will work, 16 watt increases the range of the radio over the 10 watt.

Q: Will this unit interface with a Sandel 3308?

Though explicit instructions are not available for interface with a Sandel 3308, the GNC 255A outputs 429 Arinc which can go the Sandel unit.

Q: What antenna is best for the GNC 255B considering it delivers more power compared to the GNC255A?

Any NAV/COM antenna that matches 118-136 mhz such as AV-10 or AV-17.