Barametric Altitude not getting to Transponder for ADS-B Out

[Harold Roberts]

Jonathon,

As you may recall, I have a 2016 SLSA SeaRey Elite, with the AF-5000 EFIS and a Garmin GTX-330ES Transponder. I have an ADAHRS-200/A I purchased at your recommendation due to problems with our old AHRS. Apparently my barometric pressure is not getting to my transponder as when I recently checked my PAPR ADS-B report it was missing 100% Balt data. I do see my altitude on the altitude tape. I sent the PAPR report to Garmin and they say that the barometric altitude is not getting to the GTX Transponder.

Does the barometric altitude come from the ADAHRS or from the EFIS? You stated January 2022:

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SV-ADAHRS-200 is also $1,200, cable is extra. You will need to physically install the ADAHRS and run a SkyView network cable from the EFIS to it, the old wiring should not really be reused. You will need to install and wire a new OAT. In your case, you could continue to use the EFIS internal air data computer for your pitot / static / aoa connections.
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We purchased the following kit for the ADAHRS:

What can I do to debug this problem?

[Jonathon]

Harold the EFIS gets baro altitude from the static pressure sensor in the ADAHRS, and the EFIS then rebroadcasts it to the transponder.

SeaRey schematics show the AF-5500 serial port 2 is wired for this purpose. You can confirm the AF-5500 is properly set for this by checking the SET --> CAL (hold2s) --> Admin Settings page, to verify that serial port #2 is set to TRFC/ICARUS.

You should also check the wire for continuity, it will be found between the AF-5500 EFIS main DB25 connector, pin 10, and the GTX330 HD44 connector, pin 22.

Finally, you may want to confirm that you are properly putting the GTX330 in ALT mode, and not in ON mode. In ON mode you will be broadcasting mode A and mode S (ADS-B), but you will not be broadcasting mode C altitude encoding and furthermore in ALT mode your ADS-B out broadcast will not have pressure altitude sent via ADS-B, even though the rest of your typical ADS-B out broadcast will still be sent in ON mode.