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Transponder certification question

PostPosted: Mon Feb 05, 2018 7:42 pm
by jwd3ca
Greetings...
I have installed a Becker ATC-4401 xponder using my Sport SX's internal altitude encoder. It seems to be working correctly, with the displayed xponder altitude matching my analog altimeter and so far ATC hasn't complained. I now need to have the xponder officially certified by an avionics shop. Since I don't think the shop I'll be using is familiar with the Sport SX, I want to be able to show them how to get to whatever pages are needed for them to do the job. I'm guessing that he will need to see the encoder output once his test instrument is connected. So far, I've been unable to locate this in the manual(s), so I'm hoping there is someone who can clue me in as to what I'll need to know for this procedure. Thanks!

Re: Transponder certification question

PostPosted: Mon Feb 05, 2018 8:04 pm
by Bobturner
I’ve watched my guy do this. All he needs is to be able to see the primary page with the altimeter display. His test equipment monitors the mode C by receiving the transponder output, while his vacuum pump moves the static (and pitot lines, to prevent damage) line to various altitudes. You’ll only need to dig into the manual if there’s an error.
BTW, IMHO, this test is outdated for those with modern (e.g., no cavity tubes, modern pressure transducers) equipment. It seldom fails. Also, if comparing the altimeter to transponder mode C, remember to set your altimeter to 29.92 - the mode C is always pressure altitude. And, I’m sure you know, it is technically illegal to operate the transponder until after the check has been signed off.

Re: Transponder certification question

PostPosted: Tue Feb 06, 2018 10:37 pm
by jwd3ca
Thanks, Bob, good information. Did your guy do the certification in situ? Or did you need to remove the EFIS and xponder from the panel?

Re: Transponder certification question

PostPosted: Wed Feb 07, 2018 1:06 am
by Bobturner
He doesn’t pull anything. Although he is based at my field he is totally portable. He sets up a small transponder antenna, suction cups vacuum lines to the pitot and static, and the data appears on a small handheld box while he sits in the cockpit and manually enters the altimeter readings.

Re: Transponder certification question

PostPosted: Wed Feb 07, 2018 8:42 am
by jwd3ca
Great. Thanks!