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Time for a new transponder


Davidv

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So the backstory is that in addition the 2020 compliance my KT-76A was intermittently broadcasting mode C and I would hear about it from the controllers.  Cathy from Treasure Coast avionics was kind enough to loan me another KT-76A while my new GNX-375 is waiting to be installed next month.  I haven’t had any issues until the incident today.

I was flying north at 12.5k around Lake Okeechobee when the center controller told me that an American Airbus was going to pass from my left to right ABOVE me at 11k.  I told her I’m at 12.5 and she came back and adamantly told me I was at 9200.  Both my altimeter and Stratus GPS were reading 12.5.  I told her that there must be an issue because I’m at 12.5.   She once again bluntly informed me that I was at 9.2 and not to climb any higher.  I saw the American on my ForeFlight 1K below me and knew it was in a gradual descent so I stopped arguing with her.  A few minutes later I told her that the American Jet had passed BELOW me and she still said that was impossible since I was at 9200! Needless to say I wasn’t thrilled with her way of handling the situation.

She handed me off to the next controller and he was smart enough to ask me to reset my transponder because I may have a mode C issue. 

Even though I had ADS-B on my stratus it was scary to think of the consequences of transmitting your wrong altitude to ATC...

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It makes kind of a bad situation with TCAS as well. if the airplane thinks you are somewhere that you are not and it commands a climb or a decent, you could end up hitting the other airplane. I have personally seen this on three individual instances.

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3 minutes ago, MIm20c said:

Doesn’t sound good. I would say the new equipment is a big step down in operational safety. I’d rather have one that was intermittent vs providing a gross error in altitude reporting. 

Agreed, I’m going to put my old one back in for the next three weeks until my install occurs.

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It is definitely an encoder problem. Usually, when a controller realizes that your mode C is transmitting a wrong altitude, he/she will request that you shut down the mode C portion of the transponder, so instead of selecting ALT, you select ON. That way, you won't transmit a false altitude and nobody is going to rely on false information. You might be asked a little more frequently for altitude reports, especially vacated altitudes, but that's part of the game! 

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12 hours ago, Davidv said:

So the backstory is that in addition the 2020 compliance my KT-76A was intermittently broadcasting mode C and I would hear about it from the controllers.  Cathy from Treasure Coast avionics was kind enough to loan me another KT-76A while my new GNX-375 is waiting to be installed next month.  I haven’t had any issues until the incident today.

I was flying north at 12.5k around Lake Okeechobee when the center controller told me that an American Airbus was going to pass from my left to right ABOVE me at 11k.  I told her I’m at 12.5 and she came back and adamantly told me I was at 9200.  Both my altimeter and Stratus GPS were reading 12.5.  I told her that there must be an issue because I’m at 12.5.   She once again bluntly informed me that I was at 9.2 and not to climb any higher.  I saw the American on my ForeFlight 1K below me and knew it was in a gradual descent so I stopped arguing with her.  A few minutes later I told her that the American Jet had passed BELOW me and she still said that was impossible since I was at 9200! Needless to say I wasn’t thrilled with her way of handling the situation.

She handed me off to the next controller and he was smart enough to ask me to reset my transponder because I may have a mode C issue. 

Even though I had ADS-B on my stratus it was scary to think of the consequences of transmitting your wrong altitude to ATC...

Fill out a NASA form, David

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The more scary part is think of how many don’t use flight following or talk with a controller. 

I’ve had a few king transponders go bad like you’ve described. Still good to look outside. 

-Matt

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This sounds like a bent pin on one of the grey code wires not making contact. Anytime the transponder is removed and replaced it is supposed to be recertified for this reason.

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1 hour ago, mike_elliott said:

Fill out a NASA form, David

Thanks Mike, I will.  This morning I was going through the liveATC archives hoping to find the exchange.  I found the right channel and heard the tail end of my communications on the 1630-1700Z recording, but the 1600-1630Z has largely been removed besides about 2 minutes.  I'm not pointing any fingers (and hardly think anyone would go out of their way to hide this kind of incident), but that does seem odd.

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I have a KT76 that I’m going to need to replace. Anyone have any experience with the KT74 “plug-and-play” replacement?
If it is a KT76, and not the KT76A, prepare for a completely new installation as the 76 has a different tray and connector. I learned that many years ago and now have a 330ES.

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1 hour ago, Captain Bash said:

I have a KT76 that I’m going to need to replace. Anyone have any experience with the KT74 “plug-and-play” replacement?

I had a KT76(x) and it went TU while I was on the road... (Mooney Summit)

Some guy, aka Grimmy, the Grim Reaper of all things aviation, came to my rescue...

Amazingly, Grimmy hangs out around here, often...

You might want to peruse his stash of second hand stock....

Look for @Alan Fox...

 

Best regards,

-a-

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19 minutes ago, KSMooniac said:

If it is a KT76, and not the KT76A, prepare for a completely new installation as the 76 has a different tray and connector. I learned that many years ago and now have a 330ES.

Sent from my LG-US996 using Tapatalk
 

On second look it is a KT76A.

 

 

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There are a few things that can slide in that tray...

Even digital KTs that are more modern... push button numbers... (still not ADSB, directly compliant like the KT74)

 

and this one...

https://mooneyspace.com/search/?q="Transponder for sale"&updated_after=any&sortby=relevancy

does it get any easier than that?

Best regards,

-a-

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On 6/1/2019 at 8:31 AM, 1964-M20E said:

Also if you are in a position like this if you are not in an area that requires mode C turn off alt mode.  That way ATC will have to ask you for your altitude and what you tell them is correct.

Even if it requires mode C, turn it off. No info is better than incorrect info, and you won't end up in a pissing contest with the controller. 

My guess is the A4 wire between the encoder and transponder is broken, or the encoder itself is broken.  Any good avionics shop will have the equipment to test.

Aerodon

 

 

 

 

 

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Agree on the A4 wire.  In my experience, it is the plug in the connector that is bent.  The connector is a card edge and the pins can be bent when removing and replacing the transponder.

My guess is the transponder is good.  Just not receiving the correct information from the encoder.

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On ‎6‎/‎4‎/‎2019 at 6:31 PM, Davidv said:

Yes I spoke with my avionics shop and they think it’s the encoder.  If that turns out to be the case they will replace it when they install the GNX-375 in a few weeks.

I would suggest you install GARMIN GAE 12 due to it's miniature size and it fits to the back of the GNX tray. I've installed it with my GTX335 install even with old encoder working.

 

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On 6/1/2019 at 12:19 PM, Captain Bash said:

I have a KT76 that I’m going to need to replace. Anyone have any experience with the KT74 “plug-and-play” replacement?

I replaced a KT76A with a KT74 that works with my 430W for the GPS source.  Overall I endorse the installation.  It was under 1 AMU for the installation (incl pitot-static check) plus the cost of the unit. It installed without issues.  They do need to do some added wiring, as the "slide-in" does not meet ADS-B requirements, just acts as a new Mode S transponder.  You need a connection to your 430W and to your intercom if you want voice traffic alerts.  It will give you Mode S traffic on your 430W's screen.  

I got the unit cheap as I was a Honeywell employee at the time, which was my main motivation for this solution.  Retail makes Garmin units very competitive, plus there are more options overall than there was in 2015 when I did it.  I think having ADS-B traffic in would be a nice plus.  I use a portable receiver, but an integrated solution cannot be forgotten at home.  

-dan

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On ‎6‎/‎1‎/‎2019 at 8:31 AM, 1964-M20E said:

Also if you are in a position like this if you are not in an area that requires mode C turn off alt mode.  That way ATC will have to ask you for your altitude and what you tell them is correct.

Wasn't there some AIM or FAR regarding leaving transponders in ALT mode all the time unless authorized?

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12 hours ago, Dan at S43 said:

I replaced a KT76A with a KT74 that works with my 430W for the GPS source.  Overall I endorse the installation.  It was under 1 AMU for the installation (incl pitot-static check) plus the cost of the unit. It installed without issues.  They do need to do some added wiring, as the "slide-in" does not meet ADS-B requirements, just acts as a new Mode S transponder.  You need a connection to your 430W and to your intercom if you want voice traffic alerts.  It will give you Mode S traffic on your 430W's screen.  

I got the unit cheap as I was a Honeywell employee at the time, which was my main motivation for this solution.  Retail makes Garmin units very competitive, plus there are more options overall than there was in 2015 when I did it.  I think having ADS-B traffic in would be a nice plus.  I use a portable receiver, but an integrated solution cannot be forgotten at home.  

-dan

Great info, thanks Dan! 

To clairfy, I have a KT76A.

i suspected more wiring was needed to connect to the GPS.

Any info you have regarding the Trig TT31? Does it have the same capabilities I.e. showing traffic on my 430W? It is on sale right now for $2,000 after a $500 rebate. There is also an authorized “Quick install” dealer just over the mountains in French Valley that is said to be able to install in 5-8 hours.

As for portables, my Rocket came with the GDL 39 and Aera 796 all mounted in permanent in the aircraft. It’s nice being able to have my Garmin Pilot iPad and Aera 796 all hooked up for ads-b in capabilities. The Aera is also linked to my 430W via the RS-232 connection so they talked to each other. With traffic on my 430W, I’ll have plenty of collision avoidance available for flying in busy SoCal.

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