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Transponder Problem

Capflyer

Capflyer

Well Known Member
I ran into a problem yesterday evening with my GTX327 transponder and hoping some of you with more avionics problem solving experience can help out. ATC could not pick up my transponder transmission. I was getting altitude data from my EFIS and seeing radar returns on the transponder. Apparently it was not transmitting because ATC could no pick up my squawk or altitude. I landed and rebooted my avionics and EFIS then went back up and this time picked me up. After landing at another airport for gas outside the SFRA then coming back home ATC picked me up but 15nm later they lost me. Fortunately I was visual with my home airport at the time and able to land there.

I fly out of an airport in the DC SFRA and no transponder means without question....no flying.

It was over 95deg OAT here and the cockpit was very warm especially behind the panel and foot wells. After landing I decided to pull the transponder from my panel to bring it over to an avionics shop for testing and when I did the box was very hot....as was the rest of the avionics in the panel. Could the high heat cause the transponder to intermittently stop transmitting? I checked and the unit was seated properly. An IFR pitot/static/transponder check was completed with success two months ago and since installing it have not had any issues. This was one of the hottest days I've flown this plane. Anyone have any thoughts to other possibilities?

Thanks
 
The transponder system is one of the most basic systems in the aircraft, give it power/ground and a good anttenna and it will work. Check these 2 things out and if they are good, then it's the xpdr itself.

As far as the heat, even though heat is the enemy of electronics it should still work. I doubt it was any hotter than the units I used to pull out of aircraft when I worked on the ramp at Phoenix (I was a lot younger back then), I literally used to have to wear gloves to handle them but they still worked.
 
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I concur with Walt - check th basics. If you are seeing good power, then check the antenna - I have seen bad Coax connections that just fell apart with a gentle tug. Simple stuff first!

Paul
 
Ironflight said:
I concur with Walt - check th basics. If you are seeing good power, then check the antenna - I have seen bad Coax connections that just fell apart with a gentle tug. Simple stuff first!

Paul
Click to expand...

Coax connections and grounding are the two most common problems.
 
"ALT" button pushed?

I had the same "problem".... turned out all I had to do was push the "ALT" button. Mode C ALT doesn't come on by itself when the unit is turned on.
 
Same thing...

Happened to me. I went through everything Paul and Walt suggested and even took it one step further by swapping mine with a known good one. Just happened to have another one on the field. Sure enough, it was a bad X-ponder. Had to send it in and eat the standard repair charge of $575.00 plus all the shipping. I have no idea how it happened. ELECTRONICS!!! ARGH!
Good luck!
 
Also make sure that your antenna is clean. It is possible for belly crud to create a path between the antenna and your airframe.
 
Same thing...

Happened to me the same way. Mine was working when I was in entering Green Bay Airspace and didn't work as I was leaving. I went through everything Paul and Walt suggested and even took it one step further by swapping mine with a known good one. Just happened to have another one on the field. Sure enough, it was a bad X-ponder. Had to send it in and eat the standard repair charge of $575.00 plus all the shipping.
Good luck!
 
Good Suggestions. I'll check the antenna and coax connections this evening. There is plenty of power to the unit and it showed radar returns and the encoded altitude. I may also bring it by an avionics shop to see if they can test the transmit strength. I was a little leary of the high heat theory knowing there are much hotter places than the DC area although we certainly get a lot of hot air blowing over us to the rest of the country :D

Thanks for the input.
 
Keep in mind that you have to get the unit checked every two years by an avionics shop and get that entered into your log book. When they check it ask them if your frequency is right on as a higher swr can pull the frequency, so if you have any coax or antenna problems, that can show up in the frequency check. If it looks like it may be near the edge, wiggle the connectors and antenna and see if it changes.
 
elippse said:
Keep in mind that you have to get the unit checked every two years by an avionics shop and get that entered into your log book.
Click to expand...

I just had an IFR pitot/static/transponder check two months ago and it passed with flying colors. Yesterday afternoon I decided to drop by my avionics shop with the transponder. He hooked it up to his test equipment and said it doesn't get any better. Good guy and didn't charge me to test it. It was actually interesting to see it plugged into a variety of bench testing equipment that tested the transmit strength, altitude encoding, squawk code, receive and transmit. If not something in the antenna connection he felt it was a heat related issue although he said Garmin equipment is usually not that sensitive to higher heat levels. Of course the other day it was receiving fine, picking up radar interrogations and I probably would not have seen that with a bad antenna connection.

I went back to my hanger and checked the connections and antenna, all was perfect. Flew and ATC had no issues picking me up.

Next project is to vent some moving air behind the panel to help avoid any future heat related problems to all of my panel. It was easily over 130deg around my legs the other day plus there is no insulation on my firewall.

Thanks to everyone for responding. It certainly gets the troubleshooting thought process a kick in the butt.
 
Just by removing it, you need to have it checked again in the aircraft. Here is excerpt for 94.413:
Following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system has been tested, inspected, and found to comply with paragraph (c), appendix E, of part 43 of this chapter.


Jay
 
Another GTX 327 issue

I'm aware that I am hijacking this thread, but it's about the same transponder (GTX 327) at least:

(I know that I could dig out the manuals and find the answer, but I haven't done it yet in two weeks since OSH, and this thread reminded me of the issue.)

At OSH, I had to turn my transponder "OFF" for the first time since I've been flying this aircraft.

How do I get it back to where it goes to STBY automatically again?

Every time I get in and turn on the avionics switch, it is on "ALT" already.
 
pilot2512 said:
Just by removing it, you need to have it checked again in the aircraft. Here is excerpt for 94.413:
Following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system has been tested, inspected, and found to comply with paragraph (c), appendix E, of part 43 of this chapter.


Jay
Click to expand...

Oh please. all he did was slide it out of the rack.
 
pilot2512 said:
Just by removing it, you need to have it checked again in the aircraft. Here is excerpt for 94.413:
Following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system has been tested, inspected, and found to comply with paragraph (c), appendix E, of part 43 of this chapter.
Click to expand...

Jay I respectfully disagree with your interpretation of which ever FAR you are quoting. Simply removing a transponder from the tray for a bench check does nothing to introduce any type of error. Perhaps you could also provide the correct FAR. The number of the FAR you are referring to does not come up on any type of search plus you are probably taking the wording and intent out of context. Nothing I read said anything about a transponder having to be tested while in the aircraft and Part 43 appendix F specifically says "The ATC transponder tests required by 91.413 of this chapter may be conducted using a bench check or portable equipment......."

In conclusion Part 43 does not even apply to Experimentals. Part 43.1 3 b "This part does not apply to any aircraft for which an experimental airworthiness certificate has been issued, unless a different kind of airworthiness certificate had previously been issued for that aircraft."

I appreciate your concern to keep us all legal but I think in this case I'll be just fine.
 
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The FAR's can be a bit difficult to follow sometimes, however, although I don't totally agree with Jay as far as removing and re-installing introducing errors, he is technically correct in the quote of FAR 91.413

You may want to look at FAR 91.217 which does require you at a minimum, to perform an initial correspondence check to ensure the altitude encoder is suppling correct altitude data to the transponder "as installed" in the aircraft.

This encoder check is usually accomplished in conjuction with the Part 43 appendix F transppoder check per Part 43 appendix E, paragraph (C).

Either way the encoder must be checked as installed per 91.217 initially or per 91.411 every 2 years.

PS: 14 CFR Part 91.217, 91.411 and 91.413 are applicable to all aircraft including experimental, so part 43 E/F in this case absolutely applies!

Clear as mud right :confused:

I have some of the FAR's listed my website for easy reference under "Pitot Static" and "Transponder check".
 
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To clarify my post. I used to work at a repair station. The FAA considers removing the transponder as opening the system. If not installed correctly in can introduce altitude errors. I always thought this was a little extreme myself but it came directly from the FAA. And this applies to all aircraft.

Jay
 
As one who does transponder testing, repair and certification, it is my opinion that simply sliding the transponder out of its tray and then back in does not negate the previous data correspondence tests. Some guidance is given in AC43-6B but even this document has some holes. They do, however, expect the transponder to be retested after insertion. By retesting, I assume they mean the Appendix F criteria.

Adding to what Walt said, Part 91 rules apply to all, including experimentals. If a Part 91 regulation uses a Part 43 specification, such as Appendix F, it also applies to experimentals.

Just my opinion...
 
XPDR 327

Cap Flyer
Not sure if this would apply to you but, somehow my 327 coax and marker beacon coax got swapped (by me most likely). DC ATC sometimes lost my XPDR at 30 miles 8000 feet. Works perfect now that I fixed it!
Good luck.
 
You might consider an avionics cooling fan. The GTX-327 installation manual recommends it, even though certification tests passed without one. The GTX-327 back plate includes a forced air cooling input. Cheap insurance for long and trouble free life IMHO. The manual also specifically recommends against running a blast tube into the radio. Sometimes wet & sometimes dirty air, I suppose.
 
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