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ADS-B barometric altitude encoding problem

MacCool

Well Known Member
A while ago, I replaced by AFS4500 EFIS (with internal AHARS) with an AFS 5400 using a remote mounted Dynon SV ADAHRS. After doing that, my avionics A&P noted a small static leak..OK for VFR, not IFR, he said. I ran a PAPR and it showed a new failure in barometric altitude reporting. Apparently this is usually due to "Loss of data from barometric pressure altitude source (encoder)". Transponder is a GTX327 and the ADS-B is an EchoUAT.

Thoughts on why this might be happening? Is the static leak part of the problem? Or have I missed a wiring connection between the new ADAHRS and the altitude encoder?
TIA.

..
 

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Logically, not wiring, since not 100% failure, yours only 25% of the time. Check your app once airborne, if anything is 6 or less on monitor page for NIC or NACp you are going to fail. You are aware of changing sensitivity settings. Maybe lowering improves the “sniffing” of the packet and its sees the baro part better. If wired via serially, forget the sniffing comment.
 
GTX 327 Altitude data

The GTX 327 can accept altitude data via either serial (usually from EFIS) or grey code from an encoder.
Dave
 
Yeah, the percentage failure is not consistent. Different PAPRs have shown failures ranging from 8% to 44% at different times, but always flying the same route and altitude.

The wiring is via serial connection from the EFIS. It happened after I switched EFIS's, and I did come across one or two other unrelated re-pinning errors in the install manual. I was just wondering where to start looking. I did post over on the AFS forums...maybe Rob or Shawn will shed some light.
 
You haven’t answered the important question: How does the Echo UAT get its pressure altitude data? If it gets it via hardwired RS232 from the EFIS (same source as the transponder) then you have a mystery. If it gets the pressure altitude by ‘sniffing’ (looking for the transponder signal floating around) then the answer is easy: you need to increase the sensitivity of the ‘sniffer’ in the Echo. The Echo manual should tell you how to do this.
 
You haven’t answered the important question: How does the Echo UAT get its pressure altitude data? If it gets it via hardwired RS232 from the EFIS (same source as the transponder) then you have a mystery. If it gets the pressure altitude by ‘sniffing’ (looking for the transponder signal floating around) then the answer is easy: you need to increase the sensitivity of the ‘sniffer’ in the Echo. The Echo manual should tell you how to do this.

Yeah, that's 'cause I don't know the answer to that question for sure, but on the 4500, ADS-B was also set up as a connection on serial port 3. Typically, in the 5000 series EFIS's from AFS, it's by serial from the EFIS. This EchoUAT was installed (by the A&P of the previous owner) when the EFIS was a 4500. Most of the 4500 harness was retained, for use with the 5400, but some things needed to be re-pinned. The 5400 install manual didn't mention the GTX327 as one of the things that needed to be re-pinned, but now I'm wondering. BH1166 did make a good point above...if it was wiring I would think that the PAPR would have shown either a 100% failure or a 0% failure. Besides...everything else about the EchoUAT is working fine, both OUT and IN.
 

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