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Thread: "BRG/NONE" where my heading should be. Autopilot very confused!

  1. #1

    "BRG/NONE" where my heading should be. Autopilot very confused!

    Hi everyone,

    I have a dual AF-5500 deck system in my RV-7, and I've been very pleased with it, but after a year of happy flying, it has developed a fault:

    When I engaged the AF autopilot recently, the plane veered off the set course, gradually increasing bank angle until I turned the AP off at around 45* bank. The AP seemed to work as expected for the elevator, trying it's best to keep me level. As far as I remember, the AF-Pilot screen appeared as you would expect while this was going on.

    The EFIS (PFD and MFD) both appear to be working correctly, but at the top centre of both screens is a message "BRG/NONE" where I would expect the heading (see pic 1).
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    Background is I bought this RV-7 already built, and noticed a broken wire below the panel. On investigation, I found another unrelated wire also floating in the breeze. I soldered and heat-shrinked where necessary, and removed two wires that didn't go anywhere. To add to my woes, the wiring wasn't documented when the plane was built.

    As part of trying to solve this problem myself, I've been going through the manuals, trying to document what I think should be there, and comparing it to what I've actually inspected so far. As part of this process, I've also opened a couple of D-sub connectors and been horrified by what I saw (see pic 2 3 and 4), so intermittent faults may well exist. I'm drawing up a list of D-sub connectors, pins, backshells and wire to replace these soldered horrors. Plus of course a suitable crimp tool.
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    So back to my "BRG/NONE" issue:
    Note both screens are the old OS1 models, so no fancy SV.

    Summary info below:

    EFIS1 (PFD)
    Port 0 AFS AHRS
    Port 1 AF-PILOT
    Port 2 TRFC/ICARUS (I assume this goes to the Garmin GTX328 transponder)
    Port 3 AFS ARINC (71400)
    Port 4 GTR/GNC2xx (I have a Garmin GNC255A nav/com fitted)

    GPS/NAV1 Remote GPS
    GPS/NAV2 Serial port #4
    GPS/NAV3 None

    Module config:
    Engine module HW: off NET: rxd
    Air module HW:int NET:txd
    AOA module HW:wing NET:txd
    AHRS module HW:int NET:txd
    XMWX module offline (we don't have XM in Europe)

    Diagnostics show activity on ports 0, 1 and 4, but nothing now on ports 2 or 3. Note pic 4 does show ARINC (port 3) as 'alive'.
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    EFIS2 (MFD)
    Port 0 XBOW 525
    Port 1 DISABLED
    Port 2 GTR/GNC2xx (Garmin GNC255A nav/com)
    Port 3 DISABLED
    Port 4 NMEA 9600

    GPS/NAV1 Serial port #4
    GPS/NAV2 Remote NAV
    GPS/NAV3 None

    Module config:
    Engine module HW:int NET: txd
    Air module HW: off NET:rxd
    AOA module HW:wing NET:txd (same as PFD?)
    AHRS module HW: off NET:rxd
    XMWX module offline (we don't have XM in Europe)

    Diagnostics show activity on port 4, but no others.

    The way this plane has been built and wired (eg no 'service loops') makes it tricky to access anything, and I think it not unlikely that by disturbing D-sub connectors, a soldered joint or two may have broken.

    I've tried to diagnose this myself, but being new to serial ports and having never heard of ARINC before, I've found it difficult to say the least.

    I'm getting to the point of considering how difficult (or expensive!) a complete rewire might be, so if anyone can give me any pointers, I would be extremely grateful!

    Kind regards,

    Last edited by Matt999; 06-01-2023 at 03:58 PM.

  2. #2
    A rewire may not be needed, but I would recommend playing detective and documenting your current wiring. I’m kind of anal with my documentation. I have an excel worksheet for every connector in the aircraft. Each pin is identified as to its function, wire color, and what’s connected at the other end. It will be difficult, but it’s a tremendous learning opportunity.

    I was going to mention those sub connectors, but saw that replacing them are already on your list. I picked up a used DMC crimper and the related positioners off eBay. It’s a much better crimper than some of the more inexpensive ones.

    When you hit the brg button at the bottom of the screen, what options does it present and which one is selected?
    Bob Leffler
    N410BL - RV10 - Flying

  3. #3
    The bearing pointer is just a secondary navigation indicator if for example you wanted to see what your direct radial to a VOR was, this has nothing to do with your autopilot behavior. From the symptoms described the first thing you should check is whether the shear screw on your roll servo has shorn.

  4. #4
    Thanks Jonathan,

    The shear screw is fine. On close inspection, I had a failed crimp on one of the AF-pilot roll servo control wires (pin 22). Following repair, the AP is now perfoming as expected.

    I still have other wiring/configuration problems, eg GPS/NAV1 is configured as remote GPS, when I think it should be the ARINC 71400. That may explain the "BRG/NONE" message.

    Would the following work?
    GPS/NAV2: Serial port #4 (GNC255 nav/com)
    GPS/NAV3: remote GPS

    GPS/NAV1: Remote ARINC
    GPS/NAV2: Remote NAV (GNC255 nav/com)
    GPS/NAV3: serial port #4 (GPS)

    Serial/ARINC ports are still a dark art to me, despite lots of reading. I'm making a plan while I'm waiting for Mil spec D-sub connectors etc to arrive, and I'll run it by the Forum before I start cutting any wires!

    Thanks again,
    Last edited by Matt999; 06-12-2023 at 03:52 AM.

  5. #5
    Hi Rob,
    Thanks for your input. I'm the same, and want everything documented as much as I can.
    I'm reluctant to start digging around further at the moment because the existing connections look like they might fall apart so easily.
    I've ordered lots of Mil-spec D-sub connectors and lots of wire, and new fuse boards, etc.
    I plan to set aside at least a week to start pulling apart each D-sub connector one by one, documenting whats there, extending and re-making connections along the way. Depending on how I'm getting on with my plan to correct what I think are some wiring errors, I may be able to incorporate them at the same time. Maybe later. Either way, it's going to be a long slog.

    When I hit the BRG button, the options from left to right are:
    Button 1: CDI:OFF (blue)
    Button 2: CDI:GPS (green)
    Button 3: CDI:NAV (grey)
    Button 4: CDI:AUTO (grey)
    Button 5: blank
    Button 6: GPS1 (green)
    Button 7: NAV1 (blue)
    Button 8: blank
    Button 9: INTFP (blue)

    Thanks again for your help,


  6. #6
    Quote Originally Posted by Matt999 View Post
    Would the following work?
    GPS/NAV2: Serial port #4 (GNC255 nav/com)
    GPS/NAV3: remote GPS

    GPS/NAV1: Remote ARINC
    GPS/NAV2: Remote NAV (GNC255 nav/com)
    GPS/NAV3: serial port #4 (GPS)
    GPS/NAV1 should only be configured as an ARINC if you have an IFR navigator like a 430W installed. It doesn't seem like you do since there is no serial port assigned with aviation format data like we would expect.

    The CDI is the primary navigation instrument, and what the autopilot will follow with NAV or NAV and VNAV modes active. Again, the BRG source is only a supplementary display to give you a direct bearing pointer on your HSI. Having the BRG source set to none is not of great consequence.

    CDI should be set to INTFP to navigate using your GPS puck, and the EFIS internal flight plan capability. CDI should be set to NAV1 to navigate using the GNC255.

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