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New Garmin GNC 355 GPS/COM, July 2019

I already have a GDL 82 installed with an antenna. I was wondering if I could reuse the existing GDL 82 antenna for the 355 and then use the 335 as a position source for the GDL 82? That way I would only need one GPS antenna?

If this is possible, what is the interface between the 355 and GDL 82?

Thanks!

Should be doable. The GDL82 will accept input from an external GPS source like the GNC355. You need to check the model number of your GPS antenna to see if it is valid for the GNC355.
 
I already have a GDL 82 installed with an antenna. I was wondering if I could reuse the existing GDL 82 antenna for the 355 and then use the 335 as a position source for the GDL 82? That way I would only need one GPS antenna?

If this is possible, what is the interface between the 355 and GDL 82?

Thanks!
Hello Mike,

The latest version of the GDL 82 installation manual provides configuration and wiring guidance for connecting the RS-232 and PPS signals from the GPS 175 or GNC 355 to the GDL 82 should you wish to use one of these as the GPS data source.

You have probably already thought about this, but your GDL 82 comes with a built-in GPS receiver that allows it to be an ADS-B Out device that is not dependent on any external sources of GPS data. This is a nice feature to know that even should the external navigator fail or be removed for service, you would still retain ADS-B Out capability. If you take the GPS antenna away from the GDL 82, you lose that independence. I suppose, in a pinch, you could move the antenna back to the GDL 82.

Thanks,
Steve
 
What is the difference between the GNC 355 and the GTN 635 GPS/COM?

The GNC 355 has a bit more modern intetface and software. The GTN 635 is certified to a higher level of accuracy. For example, the GNC 355 cannot be installed in turbine aircraft while the GTN 635 can. I thought the GNC 355 was going to be great for single engine aerial tankers (fire bombers) like the Air Tractor 802 series until I discovered the piston engine limitation. Bummer.
 
GNC 355 vs. GTN 635

What is the difference between the GNC 355 and the GTN 635 GPS/COM?

Jim,

Both the GTN Series Navigators and the GNC 355 are certified to the same TSO requirements for IFR Navigation.

There are some feature limitations on the GNC 355 relative to the GTN Series Navigators. The GTN Series has the ability to interface to a GSR 56 Iridium Satellite Datalink and GDL 69 Sirius XM Datalink for example. TAWS, Search and Rescue, and NVIS Capabilities are not available on the GNC 355 as they are on the GTN Series. The GNC 355 has VCALC rather than enroute VNAV capabilities. Note: This only applies to enroute VNAV, vertical guidance on approach is readily available on both series. The GNC 355 also cannot be interfaced to a Stormscope or Fuel Sensors. There is no ability for Flightplan Crossfill or Database Sync between two Navigators using the GNC 355.

Perhaps more relevant to EAB aircraft is the lack of the ability to remotely control a Remote Transponder as the GTN Series can. The G3X Touch usually handles this function however.

Please let us know if you have any other questions.

Thanks,

Justin
 
Jim,

Both the GTN Series Navigators and the GNC 355 are certified to the same TSO requirements for IFR Navigation.

There are some feature limitations on the GNC 355 relative to the GTN Series Navigators. The GTN Series has the ability to interface to a GSR 56 Iridium Satellite Datalink and GDL 69 Sirius XM Datalink for example. TAWS, Search and Rescue, and NVIS Capabilities are not available on the GNC 355 as they are on the GTN Series. The GNC 355 has VCALC rather than enroute VNAV capabilities. Note: This only applies to enroute VNAV, vertical guidance on approach is readily available on both series. The GNC 355 also cannot be interfaced to a Stormscope or Fuel Sensors. There is no ability for Flightplan Crossfill or Database Sync between two Navigators using the GNC 355.

Perhaps more relevant to EAB aircraft is the lack of the ability to remotely control a Remote Transponder as the GTN Series can. The G3X Touch usually handles this function however.

Please let us know if you have any other questions.

Thanks,

Justin

Thanks, Justin! Great, informative answer. Seems like the GTN would be overkill with the extra cost for my purpose. However, I would love a GNC level unit with Nav capability, like the GTN 650. Any chance of something like that?
 
Garmin 175/355/375 Insertion into Rack Issue

Hello - I've replaced my GNS 430 with a GNC 355. I'm trying to " rack in" the 355 and I'm having zero luck using the 3/32 hex drive tool I used on the 430 (and my other Garmin devices) to seat the 355 into the rack - the tool does not connect. I used my bore scope to look down the "tool insertion hole" - it looks like a nut in there, not a hex socket - hmmm...

Did Garmin change the tool needed, or do I have a different issue?? (I could not find anything in the 355 installation manual that mentions the tool - the 430 manual does).

Also, the 430 had a port/nipple to attach tubing for external, forced fan cooling. The 355 does not have this. I'm guessing the 355 does not use an external cooling source (internal fan is good enough)?

Thank you for your help!
 
Hello - I've replaced my GNS 430 with a GNC 355. I'm trying to " rack in" the 355 and I'm having zero luck using the 3/32 hex drive tool I used on the 430 (and my other Garmin devices) to seat the 355 into the rack - the tool does not connect. I used my bore scope to look down the "tool insertion hole" - it looks like a nut in there, not a hex socket - hmmm...

Did Garmin change the tool needed, or do I have a different issue?? (I could not find anything in the 355 installation manual that mentions the tool - the 430 manual does).

The GNC 355/GPS 175/GNX 375 use a pawl latch that is actuated with a 3/32 hex tool. This is mentioned in a couple of places in the TSO installation manual. The hex socket is recessed 1 5/8", so make sure your tool is long enough.

Also, the 430 had a port/nipple to attach tubing for external, forced fan cooling. The 355 does not have this. I'm guessing the 355 does not use an external cooling source (internal fan is good enough)?

The GNC 355 uses a thermostatically controlled internal cooling fan and does not require external cooling air.

The installation manual says "An integrated cooling fan draws air through the bezel and exhausts out the bottom of the unit. When mounting, do not block airflow to these areas. External cooling is not required.".

Steve
 
Garmin 175/355/375 Series Insertion into Rack Issue

Thank you Steve, for the reply.

Yes - my hex tool is plenty long, and the correct size. I used it racking in my GTX330ES right before trying to rack in the 355. I tried several times to find the socket before getting the borescope out to look inside the tool insertion hole. I'm afraid something is "not right" in there.

Thank you again - I guess my next step is to contact my Garmin Dealer Monday.
 
Thank you Steve, for the reply.

Yes - my hex tool is plenty long, and the correct size. I used it racking in my GTX330ES right before trying to rack in the 355. I tried several times to find the socket before getting the borescope out to look inside the tool insertion hole. I'm afraid something is "not right" in there.

Thank you again - I guess my next step is to contact my Garmin Dealer Monday.

Tim,

I use a ball end 3/32 hex tool with my GNX 375, which makes alignment easier.

Due to the deep recess, it does seem slightly more difficult to engage than my other Garmin avionics boxes, but the ball end driver makes it easy.

Steve
 
Got it - Thank you!

Steve - Got it!
Yes - I tried a ball head tool too...
After getting feedback - I zoomed in on the bore-scope picture I took and looked at it again. It appears there are two tangs partially covering the hex socket. I just had to be more aggressive in my seating of the hex tool into the socket. (never had to do that in my other Garmin devices)
Thank you again - problem solved (we like the easy ones):)
 
Hello Mike,

The latest version of the GDL 82 installation manual provides configuration and wiring guidance for connecting the RS-232 and PPS signals from the GPS 175 or GNC 355 to the GDL 82 should you wish to use one of these as the GPS data source.

Steve

I have Rev.6 (January 2020) of the GDL-82 install manual and I don't see any mention of the GNC 355 anywhere. In fact an OCR and document scan shows "GNC" appears nowhere in the text. Here is what Section 4.3 of my GDL 82 Rev. 6 installation manual states are approved GPS position sources:

GDL 82 internal GPS/SBAS with approved GPS antenna

GTN 6XX/7XX series navigators with software v6.21 or later

GNS 4XXW/5XXW series navigators with software v5.30 or later

GNS 480 navigator with software v2.4 or later
 
I have Rev.6 (January 2020) of the GDL-82 install manual and I don't see any mention of the GNC 355 anywhere. In fact an OCR and document scan shows "GNC" appears nowhere in the text. Here is what Section 4.3 of my GDL 82 Rev. 6 installation manual states are approved GPS position sources:

GDL 82 internal GPS/SBAS with approved GPS antenna

GTN 6XX/7XX series navigators with software v6.21 or later

GNS 4XXW/5XXW series navigators with software v5.30 or later

GNS 480 navigator with software v2.4 or later

Too many manuals.... :)

Rev. 2 of the GDL 82 STC (not TSO) Installation manual, 190-01810-10 says this in the revision log:
"Updated GDL 82 to v2.01, GPS/SBAS to v7.0, and added GPS 175/GNC 355 as GPS position sources."

It also includes the GPS 175 and GNC 355 in the list of approved data sources.

Steve
 
GNC 355 and GTX 327

I am installing a GNC 355 and already have a GTX 327 with a digital encoder.

The installation manual shows an interconnect drawing between the GNC 355 and GTX 3XX transponders via RS-232 channel and to use "Aviation Output 1" format. What is the reason to connect the GNC 355 to the GTX 327?

NWCBOGT.jpg
 
I am installing a GNC 355 and already have a GTX 327 with a digital encoder.

The installation manual shows an interconnect drawing between the GNC 355 and GTX 3XX transponders via RS-232 channel and to use "Aviation Output 1" format. What is the reason to connect the GNC 355 to the GTX 327?

NWCBOGT.jpg

Hello,

The GNC 355 feeding GPS Position Data via RS232 to the GTX327 will allow flight timer use and position data operation within the -327 transponder,

BR,

Brad
 
Hello,

The GNC 355 feeding GPS Position Data via RS232 to the GTX327 will allow flight timer use and position data operation within the -327 transponder,

BR,

Brad

Thanks Brad. Okay, I see about the flight timer. I guess the GTX 327 can accept "Aviation Format 1" GPS data. Why bi-directional? What is the GTX 327 sending back to the GNC 355?

I am trying to optimize my schematic before making the harnesses and want to make sure I am not adding anything unnecessary.

Thanks,

Jim
 
I am installing a GNC 355 and already have a GTX 327 with a digital encoder.

The installation manual shows an interconnect drawing between the GNC 355 and GTX 3XX transponders via RS-232 channel and to use "Aviation Output 1" format. What is the reason to connect the GNC 355 to the GTX 327?

NWCBOGT.jpg

Hello,

The GNC 355 feeding GPS Position Data via RS232 to the GTX327 will allow flight timer use and position data operation within the -327 transponder,

BR,

Brad

Hey Brad! How about pressure altitude? Will this setup also let Jim send his GTX327's encoder data to the GNC355 to enable the 355's WINDS ALOFT feature?

I'm currently planning a GNC355 installation with an existing GTX335-GPS & GAE12 encoder; each system will have its own separate GA35 antenna.

Can a GTX335-GPS send its GAE12 encoder data to a GNC355, WITHOUT configuring the GNC355 as the GTX335's position source, by connecting them as shown (for the GTX335) in Jim's diagram above using the Aviation Output 1 format?

Thanks! ZT
 
Hey Brad! How about pressure altitude? Will this setup also let Jim send his GTX327's encoder data to the GNC355 to enable the 355's WINDS ALOFT feature?

I'm currently planning a GNC355 installation with an existing GTX335-GPS & GAE12 encoder; each system will have its own separate GA35 antenna.

Can a GTX335-GPS send its GAE12 encoder data to a GNC355, WITHOUT configuring the GNC355 as the GTX335's position source, by connecting them as shown (for the GTX335) in Jim's diagram above using the Aviation Output 1 format?

Thanks! ZT

Hello,

Yes - the RS232 link back from the transponder will include Pressure Altitude data. This will assist with general information display as well as basic flight planning features. This interface is not required, so it can be omitted.

The GNC 355 Pilot's Guide details some of the XPNDR data sharing features.

BR,

Brad
Thanks Brad! But does your single "Yes" answer apply only to my first question about Jim's situation with the GNC355/GTX327 combo? Or did your "Yes" apply to my second question as well?

I would like my GTX335wGPS & GAE12 to send its encoder data to a new GNC355 but I do not want to configure the GTX335 to use the GNC355 as its ADS-B source.

Can this be accomplished via RS-232? And if so, would the proper format be Aviation Output 1, ADS-B+ FMT 1, or ADS-B+ FMT2?

ZT
 
Thanks Brad! But does your single "Yes" answer apply only to my first question about Jim's situation with the GNC355/GTX327 combo? Or did your "Yes" apply to my second question as well?

I would like my GTX335wGPS & GAE12 to send its encoder data to a new GNC355 but I do not want to configure the GTX335 to use the GNC355 as its ADS-B source.

Can this be accomplished via RS-232? And if so, would the proper format be Aviation Output 1, ADS-B+ FMT 1, or ADS-B+ FMT2?

ZT

Hello, apologies I will need to retract the previous statement.

The STC installation manual (REV3) calls out this interface with the RS232 line from the GTX 3XX and to the GNC 355. This interface/communication line has since been removed. It is reflected in the latest TSO installation manual (REV2). The GNC 355 will not receive/require any data from a GTX 3xx.

The STC manual has not been updated due to the STC Rev Cycle not being complete as of yet. So, you can omit this interface and use the latest TSO IM REV2 for guidance.

Apologies for the confusion.

BR,

Brad
 

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Hello, apologies I will need to retract the previous statement.

The STC installation manual (REV3) calls out this interface with the RS232 line from the GTX 3XX and to the GNC 355. This interface/communication line has since been removed. It is reflected in the latest TSO installation manual (REV2). The GNC 355 will not receive/require any data from a GTX 3xx.

The STC manual has not been updated due to the STC Rev Cycle not being complete as of yet. So, you can omit this interface and use the latest TSO IM REV2 for guidance.

Apologies for the confusion.

BR,
Brad
Hey Brad, It does seem a bit odd that the 355 TSO Installation Manual Rev. 2, dated January 2020 would supersede information in the newer 355 STC Installation Manual Rev. 3, dated February 2020.

In any case, how exactly is "This interface/communication line has since been removed", accomplished? Hardware change? Software update?

I mean what happens to all the GNC355/GTX3XXs already installed and connected, (many of them by certified guys), as per the GNC355 STC Rev. 3 installation instructions? Will they all suddenly cease to function correctly? Did none of them ever function correctly?

ZT
 
Hey Brad, It does seem a bit odd that the 355 TSO Installation Manual Rev. 2, dated January 2020 would supersede information in the newer 355 STC Installation Manual Rev. 3, dated February 2020.

In any case, how exactly is "This interface/communication line has since been removed", accomplished? Hardware change? Software update?

I mean what happens to all the GNC355/GTX3XXs already installed and connected, (many of them by certified guys), as per the GNC355 STC Rev. 3 installation instructions? Will they all suddenly cease to function correctly? Did none of them ever function correctly?

ZT

The current GNC does not have the software format to receive the GTX 3XX trandponder data over RS232, so it will not read the data even if that hardware communication line remains.

The dates on the certificated installation manuals don't always mean 'newest information' like in the experimental manuals, as the data within them have to follow the appropriate TSO and STC update schedules (per certification requirements). This is why there are two separate installation manuals to follow each certification line....

Nothing happens (no changes made) to fielded units - they operate the same as they were first powered up and the ports would not be configurable to operate, even if the data line was installed.

I have made our certification/product team on the 2" Navigator line aware of the conflicting information in the appropriate manuals.

BR,

Brad
 
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The current GNC does not have the software format to receive the GTX 3XX trandponder data over RS232, so it will not read the data even if that hardware communication line remains.

The dates on the certificated installation manuals don't always mean 'newest information' like in the experimental manuals, as the data within them have to follow the appropriate TSO and STC update schedules (per certification requirements). This is why there are two separate installation manuals to follow each certification line....

Nothing happens (no changes made) to fielded units - they operate the same as they were first powered up and the ports would not be configurable to operate, even if the data line was installed.

I have made our certification/product team on the 2" Navigator line aware of the conflicting information in the appropriate manuals.

BR,

Brad

Thanks Brad! I appreciate the info.

Can you tell me if the GTX335wGPS&GAE12 could RS-232 its encoder data to the GNC355 by configuring the GTX335 output as ALT FMT 1 as shown in Table 6-1 of the GTX 3X5 TSO Install Manual Rev. 9? If so, how would the GNC355 be configured?

Or is there simply no way to send the GTX335's pressure altitude to the GNC355?

ZT
 
The current GNC does not have the software format to receive the GTX 3XX trandponder data over RS232, so it will not read the data even if that hardware communication line remains. ...

BR,
Brad

I guess the better question Brad, is, do you expect the RS-232 communication line from the GTX3XX to the GNC355 will be restored/created/implemented in future GNC355 SW updates?

And does this shortcoming also affect RS-232 communications from the GTX3XX to the GPS175 and GNX375? Or only the GNC355?

Thanks! ZT
 
Currently there is no flight plan crossfill capability between the new GPS 175, GNC 355, and GNX 375 navigators and GNS/GTN, but it is something being considered.

Does anyone have an update on timeline for this? I've got two 430Ws and need to decide if I add a Flight Stream 210 or replace one of them with a GNC 355.
 
GNC 355 CDI

Steve,

Do you happen to know why the GNC355 does not provide an on-screen CDI while the GPS175 and GNX375 do? The manual states it is only available on 175/375 and not the 355, and the GNC355 iOS simulator likewise doesn't have it.

But, there's a pic on Garmin's blog for airventure 2019 showing an on-screen CDI display showing up on the 355.

Was it reverted, or perhaps it's just upcoming software? quite a useful backup to be missing if say a primary HSI on a PFD fails.

Thanks!

Sumit


Any answer to the CDI being displayed on the GNC 355?
Thanks!
 
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