ADS-B Out with KT-74

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DwayneSmithUSMC

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DwayneSmithUSMC
So. I have a KT-74 Transponder in my aircraft with no GPS. Everything about the KT-74 says that it's ads-b out capable but I've been told that I need a WAAS GPS to go with it. I don't have the kind of money to shell out for a panel mount GPS system, so my question is, can't I just hook up a WAAS GPS antenna to the KT-74 and have that work? Does that work or do I also need a WAAS gps receiver, which I then hook into the KT-74? And if so, what is a good, cheap GPS receiver that I can hook into my KT-74.

Everything on the internet about the KT-74 implies that it's ads-b out ready straight out of the box. I am very confused on this matter. Please help.
 
you need a WAAS capable GPS unit to use ADS-B out services with that unit.
 
Your transponder needs position info to work. Just running an antenna to the transponder does not make it a GPSSignal. It needs the signal from an "approved" box. The garmen GNS box has a serial data pair of wires run to the kt74 for the location info.
 
Ok. There are "approved" GPS boxes out there like the TRIG TN 70. Which is essentially a GPS receiver and antenna. The question is, can I just purchase an approved WAAS GPS and antenna and connect them to my KT 74?
 
yes, you can install an approved WAAS GPS, and antenna, connect to the KT-74, you might need a squat switch depending on the GPS, the type of plane, and maybe a different tray if you want ADS-B in and you're good to go. You should have the tray from the purchase of the KT-74. It should have been included.
 
DwayneSmithUSMC said:
Ok. There are "approved" GPS boxes out there like the TRIG TN 70. Which is essentially a GPS receiver and antenna. The question is, can I just purchase an approved WAAS GPS and antenna and connect them to my KT 74?
Click to expand...

You need to have an "approved" WAAS GPS unit that is listed on the supplemental type certificate for the KT-74 (SA00765DE). At present if I am reading the STC correctly these are the listed GPS units: GNS-400W/GNS-500W series, GTN-6XX/GTN-7XX, Bendix-King KSN-770 or 765, Freeflight 1201, Accord NexNav Mini, and the Bendix King KGX-150.
 
I'd ask an avionics shop how it works. I guess if you get an "all in one" box, it may bypass your transponder for the ADSB-out. Like others have said, the KT74 requires a WAAS source for the 2020 compliance.

If cost is an issue, the "all in ones" will definitely be most cost effective. Cheapest WAAS GPS is the 430W, and it will run you 5 figures for an install.
 
New ADS-B out is a KT74 tied to a 430W. It failed the flight test twice with a No Flight ID and NACv at 100%. The No Flight ID was that I did not know to put the N number in the ID field before take off and the shop did not tell me to. I think the install shop should have put the number in during install. On second flight today still getting 100% NACv fail. The PAPR User's Guide states:

Component and/or software compatibility with position source OR Improper system configuration

I am losing faith in the avionics shop. The KT74 Pilot's Guide has a section for Configuration Mode. It states:

The system is configured when it is first installed by your avionics
installer. Configuration items include the Mode S aircraft address,
the interface to the other aircraft systems, the aircraft category, and
the pre-programmed values for VFR squawk code

What should be in the “interface to the other aircraft systems” field?
 
Update:

Had the tech send me the Installation documentation for configuring the KT-74. They missed just about everything. Configured the KT-74 as per documentation and flew for 50 minutes. PAPR report is still fail, but only for "Air on Ground" field over 1%. All other fields are a PASS.

For the conspiracy theories out here, the airport I fly out of is about 12 miles to the nearest class C outer ring and over 20 miles to the nearest ADS-B UAT tower yet the “system” tracked me on the ground at my airport. So, with 1090ES ADS-B Out your aircraft is tracked whenever the transponder is in "On" or "ALT" mode. (Even with a 1200 squawk)

Now I only need to find out how the KT-74 knows if I am airborne or I leave it in STBY Mode and don't switch on ALT mode until I start the take off roll.
 
the box needs a flight phase switch....either tripped by airspeed or a gear squat switch.
 
Checkout_my_Six said:
the box needs a flight phase switch....either tripped by airspeed or a gear squat switch.
Click to expand...

As ...Six indicates, the STC for ADS-B use of the KT-74 requires a switch be wired to tell when the KT-74 is on the ground or flying. The choices are either a squat switch which indicates the load is off the landing gear, or an air pressure switch installed into the pitot air line to indicate when the plane has reached about 40 kts airspeed. It is explained in the STC installation/configuration instructions from Peregrine (the company that holds the STC for this and other transponders based on the Trigg TT31 electronics). Neither type of switch is included in the KT-74 package. You can get the airspeed switch directly from Peregrine for about $150.

The shop should have installed one or the other as part of the STC. Is it listed in the logbook entry? There is some configuration needed in the KT-74 to tell it if the switch is open or closed on the ground (or in the air, I don't recall which it is, but the onscreen guidance on the KT-74 configuration menu indicates which it is).
 
From the log entry there is no mention of an airspeed switch or squat switch, so I assume from the The Pilot's Guide:

Flight Timer:
Press the FUNC button once to display the Flight Timer. The Flight
Timer records the time for which the transponder has been powered
on and operating in flight mode – either ON or ALT.

This implies that the transponder transmits Airborne whenever the mode switch is in ON or ALT. If this is the case the transponder would be switched from STBY to ON or ALT at the start of the take off roll and switched back to STBY on roll out to prevent false "Air on Ground" errors.
 
bkspero said:
As ...Six indicates, the STC for ADS-B use of the KT-74 requires a switch be wired to tell when the KT-74 is on the ground or flying.
Click to expand...

Is this stated in the STC? If the shop failed to tie A/S switch or squat switch to the KT-74 is the install in compliance?
 
sounds like the install is not in compliance.....for the 2020 requirement.
 
A1Topgun said:
Is this stated in the STC? If the shop failed to tie A/S switch or squat switch to the KT-74 is the install in compliance?
Click to expand...

I am far from an expert, but the Installation instructions for the KT-74 that came as part of the STC for my transponder (about 18 months ago) say in the Preface:

"...Also, in order to be an approved installation, the ADS-B Out system equipment must be completely installed in the configurations shown within this document."

In section 3.5 (Equipment installation/Airborne status determination) it says:

"- The transponder will receive an input from an aircraft source that indicates when the aircraft is airborne. This source will be one of the following:
An airspeed switch interfaced with the aircraft pitot-static system
Note: Installation of the airspeed switch for airborne status determination is restricted to aircraft on the AML that have a maximum weight of under 6,000 pounds. For aircraft that have a maximum weight of equal to or over 6,000 pounds, a weight on wheels switch must act as the airborne status source.

- A weight on wheels switch that indicates when the aircraft is on the ground. This switch is integrated with the aircraft landing gear. The weight on wheels switch
activates when weight is detected on the extended wheels."

Sections 3.5.1 and 3.5.2 describe the details of the Airspeed or Weight on Wheels switch installations, respectively.

In the upper right corner of the KT-74 display it should indicate "GND" on the ground and "AIR" when airborne. It should change from one to the other automatically based upon the airborne status determination switch. Do you see the indication, and what does it display?
 
Switches seem a rather crude way to do this. ADS-B requires a WAAS GPS signal. Why can't the rate of change in position be used to determine when the plane is airborne?
 
GRG55 said:
Switches seem a rather crude way to do this. ADS-B requires a WAAS GPS signal. Why can't the rate of change in position be used to determine when the plane is airborne?
Click to expand...

I asked BK the same question. They didn't know why the GPS connection wasn't an option for the STC, but they were definite that only the switches were acceptable. I didn't bother to follow up with the STC holder, Peregrine.
 
bkspero said:
I asked BK the same question. They didn't know why the GPS connection wasn't an option for the STC, but they were definite that only the switches were acceptable. I didn't bother to follow up with the STC holder, Peregrine.
Click to expand...

I wonder how Garmin does it with their 330/335/345 xponders?

I am probably going to do a radio stack upgrade this winter and need to figure out what to replace my venerable old KT-76A with.
 
GRG55 said:
I wonder how Garmin does it with their 330/335/345 xponders?

I am probably going to do a radio stack upgrade this winter and need to figure out what to replace my venerable old KT-76A with.
Click to expand...

I don't know if it was a matter of Peregrine being unable to get approval using GPS data for the air/ground determination or their choice. But it is what it is. I found the pressure switch online for $22, and it added about 30 minutes and another few dollars in parts to the install. For those who's time is worth more than mine, Peregrine sells a kit with the switch and install parts for about $150.

I was in your situation with an old KT-76A (in my case one that was failing). And mine was located in a spot in the stack that made it time consuming to replace the tray (I had been quoted 10 hrs for the install with a new tray). And I have a WAAS GPS that is listed on the Peregrine STC. Those factors made it a no-brainer to buy one of the Trigg TT31-based 1090es transponders that can use the old KT-76A tray (these include the KT-74, the TT31, and IIRC the Avidyne 340). I rejected the Avidyne on price and preferred the buttons on the KT-74 to the knob-based TT31. Plus my flaky KT-76A was worth $200 as a trade in to BK. My net cost was about $2900 (that was before the price increase for the KT-74 from $2500 to $3000).

There are some limitations when using the old KT-76A tray with the KT-74. The old tray has only a single long connector where the transponder has 2. The single connector has enough lines for an ADS-B install, but will not support all the available KT-74 features. I don't remember all the details, but, for one thing, it limited me from having voice-enabled alerts from the transponder and a few other things that were not of particular value to me.
 
I went out Sunday and flew mission #5 for the FAA Rebate Verification flight. Before take off I called local TRACON and told them the plan. Turned KT-74 to ALT as I started the take off roll. Flew to Class C airspace, throttled back and circled for thirty-five minutes. Turned KT-74 OFF on landing roll out.

PAPR was clean and the GAIRS was all GREEN. Submitted my $500 rebate request.

After I get the check I will have a debrief with the avionics shop owner and if the A/S switch is not installed, I will have them install one.

This has been a real $500 rebate from HELL!
 
PS. I called the avionics shop and asked them to PDF the full Peregrine STC to me for my records.
 
GRG55 said:
I wonder how Garmin does it with their 330/335/345 xponders?
Click to expand...
Garmin uses a either a GPS speed or a change in altitude depending on how things are setup I believe.
 
A1Topgun said:
After I get the check I will have a debrief with the avionics shop owner and if the A/S switch is not installed, I will have them install one.

This has been a real $500 rebate from HELL!
Click to expand...

You can tell yourself whether or not a switch was installed and configured correctly. If you set your transponder to ALT while on the ground you should see a GND indication in the upper right of the KT-74 display screen (meaning the switch is telling the transponder that it is not airborne). On take-off you should see the GND indication change to ALT. Then on landing and slowing down below about 34 kts the indication should show GND again.

If it doesn't, then you are either missing the switch or it is misconnected/misconfigured.

BTW, if you need a copy of the full set of STC docs, I can send them. They are about 5.8 MB as a single .pdf file. Or I can send just the install and configuration manual at about 3.1 MB.
 
bkspero said:
BTW, if you need a copy of the full set of STC docs, I can send them. They are about 5.8 MB as a single .pdf file. Or I can send just the install and configuration manual at about 3.1 MB.
Click to expand...

I do not remember seeing the GND indication on the panel.
I have not heard back from the shop on sending me the STC. If you could send me the STC that would be great.
 
Took a break from the Honey-Dew list and got back out to the airport and double checked the Kt-74 configuration. Set the “Squat Switch Type” field from “NONE” to 'LOW WHEN AIRBORNE”. Recycled the transponder and it had “GND” displayed on the upper right.
 
A1Topgun said:
Took a break from the Honey-Dew list and got back out to the airport and double checked the Kt-74 configuration. Set the “Squat Switch Type” field from “NONE” to 'LOW WHEN AIRBORNE”. Recycled the transponder and it had “GND” displayed on the upper right.
Click to expand...

That is encouraging, as I believe "Low" corresponds to an open circuit for the switch. If that is accurate, then no switch (i.e., no connection) should indicate "Airborne" at all times. The fact that yours is displaying GND would mean either a switch is present and it has closed the circuit (or the unit has a shorted connector). You'll see if it switches to ALT the next time you fly.
 
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