KT74 and what else to be ADSB Out Compliant?

[jimmyjack]

I just had installed a KT76A. I am looking at the KT74 as a slide in replacement for ADSB Out compliance. What other physical boxes need installed to be legal? Apparently the transponder itself isn't enough. I don't know much about it.

 

[bkspero]

I just had installed a KT76A. I am looking at the KT74 as a slide in replacement for ADSB Out compliance. What other physical boxes need installed to be legal? Apparently the transponder itself isn't enough. I don't know much about it.

It needs a certified GPS that is on the ADSB compliant STC to provide position information, a connection from the GPS to the KT74, possibly a new transponder antenna coax if the current cable doesn't meet the specs of the STC, and at least for the GNS series GPS's the STC calls for a pressure switch to be installed in the pitot static line to deactivate the system on the ground (i.e., when the plane is moving slower than a certain speed).

As far as I know, the Garmin GNS and GTN series GPSs are on the STC, and I presume that the new King GPS is also approved (but I don't know that).

If the plane doesn't have an altitude encoder, one of those must be installed. The KT-74 will use either a Gray Code or Serial connected encoder. But I expect that the KT-76A is set up for Mode C and has an encoder.

 

[tmyers]

You will need the tray and back plate that comes with the 74 as well.

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[bkspero]

You will need the tray and back plate that comes with the 74 as well.

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As long as the KT74 is updated to the most recent firmware it may be installed for ADS-B service along with a GNS/GTN (and possibly a King) GPS using the KT-76A tray/backplate. I recall that there may be a limitation to using gray code communication with the altitude encoder (but not certain of that) due to a limited number of serial connections on the single connector of the KT-76A connector, but otherwise no tray change needed. I believe that it even allows for TIS-A output to the GPS.

King doesn't publish much installation detail for the KT-74 online (expect for dealers), so I can't provide a reference. But the KT-74 is just a Trig TT31 with a different faceplate, and Trig provides lots of info for the TT31. A reference to using the KT-76A tray for the TT31 can be found here: http://www.trig-avionics.com/products/tt31/. I later confirmed with King that the KT-74 could also be installed in a KT-76A tray for ADS-B service.

 

[jimmyjack]

Wow, thanks. This was just idle curiosity as I just spent $$$ on the 76A, but I went from dials on the xponder to dials on the xponder. I would love to have the push button interface.

 

[tmyers]

The 76A only has one connector in the backplate. The 74 has two. You can plug the 74 into a 76 tray and will have Mode S but there is no jack for the GPS and other various signals. You need the second connector to make it ADS-B out.

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[bkspero]

The 76A only has one connector in the backplate. The 74 has two. You can plug the 74 into a 76 tray and will have Mode S but there is no jack for the GPS and other various signals. You need the second connector to make it ADS-B out.

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It was that way at first, but no longer. The current KT-74 firmware enables a serial connection on the single connector common to both the KT-74 and the KT-76A, and that connector on the KT-74 can be tied into the GPS to provide position information to the KT-74 and allows it to operate in 1090es mode. The link a couple of posts above is to the Trig website (the KT-74 is just a rebranded/refaceplated Trig TT31) and you can start there to access complete information...including an installation manual which explains how to connect for ADS-B using the KT76A tray.