Advice on ADSB transponder

Greetings to all from St. Louis,

I have a Collins TDR-950 transponder. With the upcoming 2020 ADSB-out mandate the writing is on the wall for an upgrade. Have looked into the Navworks setup, seems like people are happy with it. I have already had to replace the transponder because the old one broke some of the internal gears that change the mechanical frequency wheels and a repair was not economically feasible compared to buying a whole new unit. The replacement looks brand new and works great but I want to upgrade to a newer digital model.

I would like to have the easiest transition so I am kind of leaning to the Garmin GTX-335. I like the similarity to the 327 functionality and the new tiny altitude encoder that mounts to the back of the rack. It appears to have both weather and ADSB in/out to talk to my Aera 660 GPS. I would be able to sell the Collins transponder on another website (we all know which one...). The GDL-39D I have installed could also be sold to recoup some of the cost. What I don't know is if the 335 has a built in AHARS like the GDL-39 3D to provide the platform for my Aera 660 GPS synthetic vision.

Other transponders/considerations? Advice needed,
Oly

The GTX-335 does not have an internal AHRS. You also have to buy the unit with the internal GPS if you don't already have an approved external position source. It costs about $800 more than the base unit.

less expensive alternative is the Stratus ESG from Appareo.

Trust me, no one is happy with Navworx right now

You should check out the other messages on the site regarding Navworx a little more in depth. FAA approval of these units is under heavy scrutiny right now, and the future lifespan of this equipment is in question.

I have the EXP unit in my RV6, and functionally, I love it. I'm just worried that the FAA is going to tell me I can't use it at some point in the future. It's still early and everything might turn out okay, but I'd bet more money on a coin flip right now.

Don

335 vs 345

Maybe it was a simple typo, but I believe only the (more expensive) GTX 345 provides ADS-B in traffic/wx. The 335 mentioned satisfies the requirements for ADS-B out at a lower cost but without the benefit of "in" services.

I'm currently weighing all my options as well. It gets complicated (and pricey) pretty quickly!

olyolson said:

Greetings to all from St. Louis,

I have a Collins TDR-950 transponder. With the upcoming 2020 ADSB-out mandate the writing is on the wall for an upgrade. Have looked into the Navworks setup, seems like people are happy with it. I have already had to replace the transponder because the old one broke some of the internal gears that change the mechanical frequency wheels and a repair was not economically feasible compared to buying a whole new unit. The replacement looks brand new and works great but I want to upgrade to a newer digital model.

I would like to have the easiest transition so I am kind of leaning to the Garmin GTX-335. I like the similarity to the 327 functionality and the new tiny altitude encoder that mounts to the back of the rack. It appears to have both weather and ADSB in/out to talk to my Aera 660 GPS. I would be able to sell the Collins transponder on another website (we all know which one...). The GDL-39D I have installed could also be sold to recoup some of the cost. What I don't know is if the 335 has a built in AHARS like the GDL-39 3D to provide the platform for my Aera 660 GPS synthetic vision.

Other transponders/considerations? Advice needed,
Oly

Click to expand...

Oly,

I replaced my Garmin GTX 327 with a Garmin GTX 345 to become ADSB out compliant and gain ADSB in capability along with the benefits of AHRS. I use my Garmin 430 W for the GPS position source. I use the ICARUS altitude encoder that drives my AFS 4500 for the GTX 345. If I were to do it all again, I would have bought the Garmin ALT encoder module.

Like you, I have a Garmin Aera 660. My Aera 660 interfaces very well with the Garmin 345 via bluetooth and now the Garmin barewire connection/interface. The interoperability is amazing. I also connect my GTX 345 to my ipad using Foreflight via bluetooth. I couldn't be more pleased with this combination. The Garmin 345 works and looks like my old 327 only better. I really like that the 345 only requires the one antenna to transmit and receive ADSB in.

I believe the NAVWORX system and for that matter, Garmin GTX 335 with GDL 39D requires two antenna. One to transmit and another to receive ADSB in.

I considered NAVWORX because it cost a little less and it interfaces with the AFS 4500 EFIS I have. I'm glad I decided not to go that route. Seems NAVWORX is having issues with the FAA.

Lastly, the service and support I have received from the Garmin experts has been excellent. Steve from Garmin is exceptional.

I think my next purchase will be the Garmin G5 to replace a couple of steam gauges.

As the above posts imply, we need to know what other equipment you already own, and what you're looking for wrt ADSB-in, before reasonable recommendations can be made. In my case, I already owned a GRT HX, a Garmin 420W, and a Skyradar ADSB-in. For me selling my G 327 transponder and replacing it with a remote mounted Trig TT-22 seemed to be the best option.
PS If you're doing this in the next 4 months go sign up for the FAA's $500 rebate.

TRIG

Because of Navworx's problems think I'll go ahead and buy a Trig TT31 to replace my King 76A. It's supposed to slide into my existing tray. I'll use my Garmin 400W for the GPS source and my ilevil/iFly combination for ADSB-in. I understand there is an airspeed switch that has to be purchased, but with the rebate, and self install I should be less than $2000 out of pocket. John

jpowell13 said:

Because of Navworx's problems think I'll go ahead and buy a Trig TT31 to replace my King 76A. It's supposed to slide into my existing tray. I'll use my Garmin 400W for the GPS source and my ilevil/iFly combination for ADSB-in. I understand there is an airspeed switch that has to be purchased, but with the rebate, and self install I should be less than $2000 out of pocket. John

Click to expand...

Sounds like a good plan. You will need to add wires to the back of the tray (airspeed switch, 400W connection). You will need the latest Garmin software on the 400W (you need "ADSB+" output).

jpowell13 said:

Because of Navworx's problems think I'll go ahead and buy a Trig TT31 to replace my King 76A. It's supposed to slide into my existing tray. I'll use my Garmin 400W for the GPS source and my ilevil/iFly combination for ADSB-in. I understand there is an airspeed switch that has to be purchased, but with the rebate, and self install I should be less than $2000 out of pocket. John

Click to expand...

The airspeed switch is required for the STC, so if it's a certified plane you need that. Otherwise you don't.

Jesse said:

The airspeed switch is required for the STC, so if it's a certified plane you need that. Otherwise you don't.

Click to expand...

So does the TT31 auto switch from ground to air mode (based on GPS ground speed?)? Automatic switching of some sort is required.

BobTurner said:

So does the TT31 auto switch from ground to air mode (based on GPS ground speed?)? Automatic switching of some sort is required.

Click to expand...

Been there. Done that.

My installer would not do my install without the speed switch.
Also, make sure the Trig has the latest software. You have to change out the tray but the KT76 connector plugs right up. You will need additional wiring to your position source, RS232, etc. The Trig cuts down on install costs, but there is additional work to do.

Good luck

Ben Meyer

jpowell13 said:

Because of Navworx's problems think I'll go ahead and buy a Trig TT31 to replace my King 76A. It's supposed to slide into my existing tray. I'll use my Garmin 400W for the GPS source and my ilevil/iFly combination for ADSB-in. I understand there is an airspeed switch that has to be purchased, but with the rebate, and self install I should be less than $2000 out of pocket. John

Click to expand...

It will slide in and work as a regular transponder. If you want to use the ADSB mode S function you will need to wire it to an approved GPS, i.e. 430/650...

To do this you will need to install the Trig mounting tray. The KT76 tray has a large 36 pin I believe, connector and the new tray has two connectors. It's easy if you are comfortable with wiring. If I remember correctly, I just moved the KT76 plug no the back of the Trig tray and wired the GPS into the new 9 pin plug required on the Trig. Look at their manual and you will understand all this.

Mine does not have a speed switch and it works perfectly. Up and running for over a year with several reports from the FAA to verify various settings.

So, it's true it is a plug and play with the KT76, but not true to get the ADSB function you are looking for.

Hope this helps.

RE:TT31 "Speed Switch"

The Trig TT31 install manual contains the following info:

12.4 Automatic Air/Ground Determination
The TT31 can report ADS-B surface and airborne messages. The ADC or squat switch inputs can be utilized to determine air/ground status.....

I didn't find anything in the TRIG install manual that specified that a speed switch was required but it does mention that an airspeed switch can be used in lieu of a Squat switch to indicate on ground status. Recently, I have noticed several people reporting getting "Air on Ground Faults" in their ADS-B performance report from the FAA, so the transponder does need something that it can use to determine air/ground status.

For basic altitude reporting with a Mode A/C transponder you all ready have the transponder connected to an altitude source for pressure altitude either parallel Gray code or an ADC RS232 serial output. If you have Dynon, GRT, AFS, Garmin or similar EFIS in your aircraft you are most likely providing the transponder with altitude info via an RS-232 ADC ouput from the EFIS which contains 'airspeed' data. Per the install manual the TRIG 31 will use airspeed data from the ADC input to determine air/ground status so a dedicated squat switch or airspeed switch would not be required.

Amazing what you learn from experienced hands on this site. I was wondering how my existing tray could work even though Trig add says it does. Now I know the truth. Still, seems like the least painful option to get ADSB-out. John

Isaac said:

. Recently, I have noticed several people reporting getting "Air on Ground Faults" in their ADS-B performance report from the FAA, so the transponder does need something that it can use to determine air/ground status.
.

Click to expand...

I have been checking this out lately. It seems the FAA test specs are pretty stringent. If I land and immediately brake to get below the airspeed where my transponder goes to ground mode, I pass the 'air on ground' test. But if I let it roll at some moderate speed above the switch point, down the runway for 30 seconds or so (fuel tanks are near the far end) then I fail the above test.

The Trig TT22 installation manual, by contrast, has very little detail on its "Squat Switch" input, other than to say it is programmable for active high or active low and that if no switch is present the transponder must be configured to disregard this input.

As such, I would be interested to know how the TT22 fares in the FAA "air on ground" test. Anybody out there with experience who would care to share it, please?

RV8iator said:

It will slide in and work as a regular transponder. If you want to use the ADSB mode S function you will need to wire it to an approved GPS, i.e. 430/650...

To do this you will need to install the Trig mounting tray. The KT76 tray has a large 36 pin I believe, connector and the new tray has two connectors. It's easy if you are comfortable with wiring. If I remember correctly, I just moved the KT76 plug no the back of the Trig tray and wired the GPS into the new 9 pin plug required on the Trig. Look at their manual and you will understand all this.

So, it's true it is a plug and play with the KT76, but not true to get the ADSB function you are looking for.

Hope this helps.

Click to expand...

Well you 'can' use the new tray and the additional plug provided or you can use the original 76A tray and wire the GPS to the serial port provided (pin 7)on that plug, the additional plug gives you some extra options for RS232, audio and ARINC, but it is not required.

And just to clarify, the TT31 will slide into a KT76A rack only, not a straight KT76 which has a different connector.

jpowell13 said:

Amazing what you learn from experienced hands on this site. I was wondering how my existing tray could work even though Trig add says it does. Now I know the truth. Still, seems like the least painful option to get ADSB-out. John

Click to expand...

Hate to say it but its also amazing how much misinformation is available.

Canadian_JOY said:

The Trig TT22 installation manual, by contrast, has very little detail on its "Squat Switch" input, other than to say it is programmable for active high or active low and that if no switch is present the transponder must be configured to disregard this input.

As such, I would be interested to know how the TT22 fares in the FAA "air on ground" test. Anybody out there with experience who would care to share it, please?

Click to expand...

I have a modified TT-22 from GRT, where the GRT HX provides the control link instead of the usual small panel box from Trig. A Garmin 420W provides RS232 'ADSB+' data to the remote transponder. GRT sent me new HX software so it sends a software signal to change from air to ground mode as indicated airspeed drops below 30 kias.
As I note in previous posts, I pass the FAA tests as long as I promptly brake on landing. If I let it roll at a modest speed (like 25 knots plus a 10 knot headwind) for 30 seconds or so, then I fail the air-on-ground test. It seems that the FAA test is overly demanding on this spec.
Edit added: So obviously it is possible to switch with software, but I know of no open source for it. If you can somehow rig a 'weight on wheels' switch, that clearly is a straightforward path forward.

Bob - thanks for sharing this info. When you say the GRT sends a software signal to the TT22, is this being done across the TT22 control lines (TMAP signals), or is this new GRT software triggering a discrete output from the HX to drive the Squat Switch input on the TT22? If I'm interpreting your words correctly, I think you're saying the GRT HX is sending "on ground" in digital format across the TMAP control lines, and that the TT22 is able to strip off these "on ground" data bits and use them to trigger an "on ground" response from the transponder.

If this is the case I'm a bit bummed since I went with the TC20 control head for the TT22 as a means of making IFR certification a bit easier (must use a TSO'd altitude encoder here). Now it seems I'll have to consider wiring in an airspeed switch or something similar in order to achieve ADSB certification. Isn't it wonderful how a regulatory body can make compliance with their regulations more difficult?

OK, now I get to show the world how dumb I can be...

As it turns out, I found in my email records a brief discussion with the support folks at Trig (who, by the way, provide excellent support!). I had noticed the need for the squat switch in the TT31 STC and asked if it was required for the TT22/TC20 combo. Below is the response I received. Yeah, you guessed it, I filed it away in my records and forgot it. DOH!

"Having spoken to our STC expert, I have a small correction to make. You only need a second air/ground determination solution if you use an ADC, because apparently they are too unreliable. So using GPS ground speed alone is actually ok. "

To answer your question: the HX sends RS232 signals to a small adaptor mounted directly on the remote Trig. The adaptor changes the format to Trig's format. It's all software, no connection to the squat input.

Thanks for confirming the TT22 is capable of reading some sort of digitally-encoded "I'm not flying anymore" message. I've reached out to Trig support to see if I can get a better understanding of why the transponder doesn't seem able to make this determination accurately using the data provided in the ADSB+ data stream from the GPS navigator, or if the functionality you saw prior to your latest HX software update was an artifact of the transponder being controlled by the HX.

Canadian_JOY said:

Thanks for confirming the TT22 is capable of reading some sort of digitally-encoded "I'm not flying anymore" message. I've reached out to Trig support to see if I can get a better understanding of why the transponder doesn't seem able to make this determination accurately using the data provided in the ADSB+ data stream from the GPS navigator, or if the functionality you saw prior to your latest HX software update was an artifact of the transponder being controlled by the HX.

Click to expand...

When the software was written there was no 'air on ground' spec,and GRT put in an extra 30 second delay 'just to be sure'. Then the FAA changed the rules (again). So the software change is to just delete the extra 30 second delay. Yes, in my set up the air or ground status is sent to the 22 by the HX.