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Thread: ADS-B barometric altitude encoding problem

  1. #1

    ADS-B barometric altitude encoding problem

    Six months ago, I replaced my AFS4500 EFIS with an AFS 5400. After doing that, my avionics A&P noted a small static leak..OK for VFR, not IFR, he said. I then ran a PAPR and it showed a failure in ADS-B barometric altitude reporting (previous PAPR's were fine). Transponder is a GTX327 and the ADS-B is an EchoUAT. Navigator was a 430W, now is an IFD440. Switching the GPS navigator didn't make the problem worse or better.

    Thoughts on why this might be happening? Is the static leak part of the problem? Or is it more likely that I've mis-configured the serial ports from the 5400? (I have the 5400 as the PFD and a second 3500 attached to the 5400 via ethernet cable). FWIW, the ADS-B IN trf/wx function of the EchoUAT works fine and displays on the 3500. The only part of the ADS-B OUT that fails is the barometric altitude reporting, and it only fails a percentage of the time, not 100% of the time.

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  2. #2
    OK, no-joy. Let me ask it this way... my ADS-B out was working fine with the old AFS 4500/Crossbow. When I switched it out for the 5400 with SV network, the ADS-B is no longer getting barometric altitude encoding from the new EFIS . Why might that be? The serial port setup, 4500 vs 5400 is the same.
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    Last edited by MacCool; 01-04-2022 at 06:50 AM.

  3. #3
    Could be the static leak, could be altitude encoding. You don't have a single serial port on your 5400 assigned to TRFC/ICARUS so as to send altitude encoding to your GTX 327, which means

    1) you either have a hardware encoder, or
    2) you have a serial port on your 3500 MFD assigned to TRFC/ICARUS and connected to your GTX327. In such case your 3500 must either have its own internal AHRS and air data, or otherwise be properly set up to receive data from the 5400's SV-ADAHRS-200 by way of the Air Module Config and AHRS Module Config both being set to HW:OFF, NET:RXD, or
    3) your transponder just isn't getting encoding at all.

    The ADS-B in from your echo working properly is immaterial to the functioning of your ADS-B out, so there is nothing about that which merits further inquiry.

  4. #4
    Just an update, as I've had a few queries via PM from pilots that were having the same or similar problem.

    Regarding most of avionics, I am generally a total noob. I've been flying airplanes (certified) a long time but until I bought this RV-9A two years ago, my sole approach to maintenance and avionics was to take the plane to my A&P and/or avionics guy. The world of Experimental forces a re-thinking of that because I can't find anyone within 200 miles that knows ANYTHING about Advanced Flight Systems avionics in particular and glass EA-B in general. If I want to keep this plane flying and navigating, I have to rely on info from forums like this, or phone calls to AFS. AFS is very generous with accommodating those conversations, but each conversation is like trying to get a sip of water from a fire hose. It often assumes knowledge that I just don't have yet. I don't even really know how to frame the questions.

    Anyway.... long story short, based on Jonathon's post above and sheer intuition and guesswork on my part, I changed the AHARS and Air Module settings in the 5400 (transmit) and in the 3500s (receive), and now things are working normally (0.0% BAlt failure) according to the PAPR that I ran today from a flight I did on Saturday.
    Last edited by MacCool; 05-26-2022 at 09:43 AM.

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