Options for replacing a Bendix King KT-76C Transponder

Do you already have a WAAS GPS to feed position data to a Mode S transponder for ADS-B-out? If not, are you planning to get such a GPS in the foreseeable future? If the answers to both are "no", installing a Mode S transponder doesn't get you much benefit.
 
Mode-S and ADSB readiness are thoughts for the future. Our current GPS is non-WAAS KLN-94. I figure that since we need to replace our current one, why not get ready. KT-76C units are on eBay $750 and up. IIRC these units are about $3k
 
You could replace the KT-76C with a used one for around $1500.00 *

You could replace it with a KT-76A for $800.00 or so.*

These are the "slide in" replacement options.

I have put 2 Garmin 327's in RV's in the past two weeks that were also around $1500.00 but had to have new trays and electron hoses...*

(*Bennett Avionics w/ limited warranty)


Transponders croaking...must be a Christmas thing :yikes:!



Hope this helps;

Chris
 
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the new King Kt74 is a slide in replacement, gets you 2020 compliant with a new tray and limited labor. Can't use ADSB in without a WAAS GPS though.
 
How did you transponder "die" so that it's not repairable?
 
If you fly above FL180 or internationally, you'll eventually need a 1090ES transponder anyway. Might as well go in that direction now, even if you don't put the GPS source in at this time.

If you do not fly above FL180 or internationally, a 978 Mhz UAT is much more bang for your buck for ADS-B compliance. In such case, I'd put in the least expensive slide-in compatible Mode C transponder you can find for now. Save your big $$ for a UAT in the future.
 
Pedals2Paddles said:
If you fly above FL180 or internationally, you'll eventually need a 1090ES transponder anyway. Might as well go in that direction now, even if you don't put the GPS source in at this time.

If you do not fly above FL180 or internationally, a 978 Mhz UAT is much more bang for your buck for ADS-B compliance. In such case, I'd put in the least expensive slide-in compatible Mode C transponder you can find for now. Save your big $$ for a UAT in the future.
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FL180 exceeds the service ceiling of the C-172S.
 
King equipment is usually very repairable. They fixed mine a few years ago at no charge, 10 years after the warranty had expired.
 
If that's your aircraft, then it's also unlikely you'll be talking to Eurocontrol anytime soon either. I'd not waste several thousand on a 1090ES transponder. It's only benefit is to the government, and nothing back at you. And the government doesn't even use it yet. Whereas an installed UAT can give you weather and traffic back to your panel and portable devices. I'd save your money for the more useful device and buy a cheap used transponder.
 
Pedals2Paddles said:
If you fly above FL180 or internationally, you'll eventually need a 1090ES transponder anyway. Might as well go in that direction now, even if you don't put the GPS source in at this time.

If you do not fly above FL180 or internationally, a 978 Mhz UAT is much more bang for your buck for ADS-B compliance. In such case, I'd put in the least expensive slide-in compatible Mode C transponder you can find for now. Save your big $$ for a UAT in the future.
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Where is 1090 mandated or planned to be mandated outside the US? I agree that if you have an operational need to fly at and above 18,000 MSL that 1090ES is a given, but unless you plan on a flight to Australia, 1090ES is not mandated for the typical GA piston. NavCanada will implement ADS-B using 1090ES, but they say it will not be mandated. At this point, it is only used over the Hudson Bay for those at FL290 and above. Even still, it is not mandated for use in that airspace.
 
retailguy said:
the new King Kt74 is a slide in replacement, gets you 2020 compliant with a new tray and limited labor. Can't use ADSB in without a WAAS GPS though.
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Yes it is a slide in replacement, but as a slide in, it will not meet the 2020 mandate for ADS-B Out. To meet the mandate, one must also have a suitable position source and the pair must be approved via a TC, STC, or follow on field approval. In the OP's aircraft as described, there isn't a suitable position source. ADS-B In is not part of the mandate, so does not need to have a WAAS GPS.
 
On the same note as posted I have a NARCO transponder in my Beechcraft Sport. It's not working, will not turn on. I fly in SE Alaska and into Canada from time to time. Have not flown in a controlled airspace that requires a transponder in years. What are my options??
 
John Collins said:
Yes it is a slide in replacement, but as a slide in, it will not meet the 2020 mandate for ADS-B Out. To meet the mandate, one must also have a suitable position source and the pair must be approved via a TC, STC, or follow on field approval. In the OP's aircraft as described, there isn't a suitable position source. ADS-B In is not part of the mandate, so does not need to have a WAAS GPS.
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Standalone ADS-B qualified GPS boxes are available for the KT-74, and will of course require a new antenna.

The big question is installation labor compared to just replacing your current transponder with a working used unit of the same or similar type.

If you want to wait for ADS-B out then go with a direct replacement.

If you want to consider the KT-74 you should probably get an estimate from your local avionics installer of the cost of a KT-74 + WAAS box + installation compared to other alternatives like the FreeFlight or Garmin 978mhz solutions.
 
JimNtexas said:
Standalone ADS-B qualified GPS boxes are available for the KT-74, and will of course require a new antenna.

The big question is installation labor compared to just replacing your current transponder with a working used unit of the same or similar type.

If you want to wait for ADS-B out then go with a direct replacement.

If you want to consider the KT-74 you should probably get an estimate from your local avionics installer of the cost of a KT-74 + WAAS box + installation compared to other alternatives like the FreeFlight or Garmin 978mhz solutions.
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The FreeFlight 1201 is being sold for $2985 not including the GPS antenna which will run another $400. I can't find an Accord NexNav Mini for sale, but there is one price provided in a new release at $5775. This is above the cost of the transponder.

Unless the GPS sensor is integrated into the unit as is the case with the NavWorx 600BG, Free Flight Ranger, or Garmin GDL84/88, the position source is the largest portion of the price. Several manufacturers are threatening to announce a transponder with a built in position source, but as of today, these are only threats. I expect an integrated position source will add $1000 to $1500 to the price of a transponder when you include the cost of the antenna.
 
John Collins said:
Yes it is a slide in replacement, but as a slide in, it will not meet the 2020 mandate for ADS-B Out. To meet the mandate, one must also have a suitable position source and the pair must be approved via a TC, STC, or follow on field approval. In the OP's aircraft as described, there isn't a suitable position source. ADS-B In is not part of the mandate, so does not need to have a WAAS GPS.
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True, the tray has to be replaced. But he could use it now, without the tray replacement and then do that down the line close to 2020.

My point, is, I believe that is his cheapest way to get compliant currently on the market.
 
retailguy said:
True, the tray has to be replaced. But he could use it now, without the tray replacement and then do that down the line close to 2020.

My point, is, I believe that is his cheapest way to get compliant currently on the market.
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It is a lot more than a tray replacement to become compliant. You also need to add a WAAS position source, that should be able to be purchased for $4000 to $20000 extra. A cheaper solution would be to install a UAT system with a built in WAAS position source. That does not solve the transponder replacement, but that can be done with a like type as the cheapest option.
 
retailguy said:
True, the tray has to be replaced. But he could use it now, without the tray replacement and then do that down the line close to 2020.

My point, is, I believe that is his cheapest way to get compliant currently on the market.
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Need a definition of "tray".
 
John Collins said:
It is a lot more than a tray replacement to become compliant. You also need to add a WAAS position source, that should be able to be purchased for $4000 to $20000 extra.
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I think you're way overstating the cost of adding a standalone WAAS GPS to a KT-74 installation.
 
JimNtexas said:
I think you're way overstating the cost of adding a standalone WAAS GPS to a KT-74 installation.
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Just stating the list prices for the equipment that is specified as being approved for this unit plus installation. The low end is the FreeFlight 1201 $2889 plus GPS GA35 antenna $349 plus installation. The high end is a GTN750 $16,900 plus a GI 106A CDI $2,599 plus installation.
 
Jaybird180 said:
Need a definition of "tray".
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A tray is the aluminum case which is mounted in the avionics rack and that the KT74 slides into to mate with the connectors to power and ground and the other interfaced components of the installation. The original KT76C uses one connector at the rear of the unit. The KT74 uses two, although the second connector is not needed in all ADS-B installations. Regardless, additional wires need to be added to the existing connector to interface to a position source.
 
Im waiting for a drop in replacement for my King Transponder and no, I don't have WAAS and there is no getting around another antenna (a GPS one). There are thousands like me so it will be here. I have no more room in my panel or tray, so it has to fit the King footprint.

Don't forget, you'll still be able to fly up to 2500AGL without one according to the current rules. And, they probably wont enforce it right away. There will be a transition period.
 
John Collins said:
A tray is the aluminum case which is mounted in the avionics rack and that the KT74 slides into to mate with the connectors to power and ground and the other interfaced components of the installation. The original KT76C uses one connector at the rear of the unit. The KT74 uses two, although the second connector is not needed in all ADS-B installations. Regardless, additional wires need to be added to the existing connector to interface to a position source.
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That's what I thought a tray was. What is retail guy referring to in 18? Are trays custom made one offs or something that require FAA Certification?
 
Jaybird180 said:
That's what I thought a tray was. What is retail guy referring to in 18? Are trays custom made one offs or something that require FAA Certification?
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I guess he is expecting that you have to use a signal that is only located in the second connector. The original tray would not have a cutout to mount the second connector, whereas a tray made for the KT74 would. It really depends on if the second connector uses a feature or function one would need for a particular installation. The second connector is used for an additional serial interface and an ARINC 429 interface. The latter may be used to connect Mode S TIS (not TISB which is an ADS-B feature) to display on a GNS430W/530W or other compliant display that supports Mode S TIS using this interface. All the basic signals for ADS-B are contained in the original connector.
 
John Collins said:
I guess he is expecting that you have to use a signal that is only located in the second connector. The original tray would not have a cutout to mount the second connector, whereas a tray made for the KT74 would. It really depends on if the second connector uses a feature or function one would need for a particular installation. The second connector is used for an additional serial interface and an ARINC 429 interface. The latter may be used to connect Mode S TIS (not TISB which is an ADS-B feature) to display on a GNS430W/530W or other compliant display that supports Mode S TIS using this interface. All the basic signals for ADS-B are contained in the original connector.
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Then how do they advertise slide in replacement? What does a tray cost? Is it allowable per the rules to modify the existing tray? Can an owner manufacture a part to their own specifications and have it approved (recall reading something about that - not sure where)?
 
Jaybird180 said:
Then how do they advertise slide in replacement? What does a tray cost? Is it allowable per the rules to modify the existing tray? Can an owner manufacture a part to their own specifications and have it approved (recall reading something about that - not sure where)?
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As a slide in, it is a replacement. To hook it up for ADS-B, the same tray can be used, but wiring is required along with an appropriate position source. Yes, owners can produce their own parts, see AC 20-62E for details. It would be a waste of time and money to not just use a KT74 tray if you had a reason to use the other signals in the second connector. But if you had no need, why would you care? Replacing the tray is not a big deal. You remove the screws holding the tray in place to the rack, remove the connectors and then reverse the process with the new tray. An hour or so of labor? To install a new transponder with a totally different set of connectors and tray would probably run 8 + hours of labor.
 
Clearly I have a misunderstanding somewhere, so forgive the pedantic way of finding the source of missing or incorrect understanding.

When a unit is purchased what comes in the box?
When they say "slide in" or "replacement for unit xxx" does that mean the same thing?
If a unit is a "slide in", like in my case would we get same functionality with a new face if we just use the existing wiring harnesses, etc and hook everything up the same way?
Is this required to be done by a certified mechanic or can an owner do a "slide in" replacement?

BTW- this thread is now educational versus advice, as our transponder problem is rectified. I do not know yet what our MO decided to do, but he did ask my help then told me he would be in touch.
 
Jaybird180 said:
Clearly I have a misunderstanding somewhere, so forgive the pedantic way of finding the source of missing or incorrect understanding.

When a unit is purchased what comes in the box?
When they say "slide in" or "replacement for unit xxx" does that mean the same thing?
If a unit is a "slide in", like in my case would we get same functionality with a new face if we just use the existing wiring harnesses, etc and hook everything up the same way?
Is this required to be done by a certified mechanic or can an owner do a "slide in" replacement?

BTW- this thread is now educational versus advice, as our transponder problem is rectified. I do not know yet what our MO decided to do, but he did ask my help then told me he would be in touch.
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Each manufacturer is different in terms of what comes in the box. Bendix King normally just includes the unit. An installation kit is often packaged separately and typically includes the connectors, pins, and tray, although they can be purchased separately by part number.

I interpret a slide in as having the same physical size and rear connectors that interface to the existing tray and wiring harness and provide the same functions without needing modification. In some cases, new functions may require the addition of a new tray, and or new wires added to the existing connectors, and or a new connector with totally new wires.

A replacement does not necessarily mean it is slide in. It may be a different form, require a rewire to different connectors, etc. A log book entry for such an installation would read something like "Removed KT76A transponder SN1234, replaced with Garmin GTX327 SN56789 transponder, ..."

IMHO, you should be able to install a transponder that is a slide in, but the FAA does not agree with me as it is explicitly excluded as preventive maintenance which may be performed by a pilot/owner. CFR 14 Part 43, Appendix A (c) Preventive maintenance lists 31 tasks that are not considered maintenance and can be accomplished by the pilot-owner and the relevant task is quoted below:

(31) Removing and replacing self-contained, front instrument panel-mounted navigation and communication devices that employ tray-mounted connectors that connect the unit when the unit is installed into the instrument panel, (excluding automatic flight control systems, transponders, and microwave frequency distance measuring equipment (DME)). The approved unit must be designed to be readily and repeatedly removed and replaced, and pertinent instructions must be provided. Prior to the unit's intended use, and operational check must be performed in accordance with the applicable sections of part 91 of this chapter.
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Ah, I recall reading that when the transponder started going buggy, and I entertained the thought of pulling it, cleaning and reseating the connectors when I was away from home base.
 
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