ADS-B message

[GlennB]

We've been getting instances lately of a momentary white-on-grey (i.e. low priority) message alert.  It's accompanied by the audio "message" and might happen half a dozen times in a flight or not at all.

A check of the datalogs shows that it's related to a loss of GPS data to the ADS-B output.  There is no other indication of GPS problems - course information on the HSI, wind vector, mapping on the GPS itself etc are all solid.

These data dropouts are very brief, as the message always self-clears in less than a second.

I'm pretty convinced this only emerged with the latest V.14 firmware.  Is it somehow more sensitive to the occasional dropped sentence, or is there somewhere else I should look?

 

[Dynon]

What exact version are you on?

And what is your ADS-B Out position source? (SV-GPS-2020, SV-GPS-250, external IFR gps, etc)

 

[GlennB]

Sorry, should have told you this with the first post:

What exact version are you on?

I'm away from the aircraft at the moment, but it's the latest release which would make it 14.2.1.

And what is your ADS-B Out position source? (SV-GPS-2020, SV-GPS-250, external IFR gps, etc)

It's a Garmin 795.  I also checked its firmware to be the latest, but again can't quote you the version number.

 

[Dynon]

It's possible that the transponder position processing is discarding position updates that do not validate for some reason - we're not able to qualify all of the external non-certified possibilities that one could possibly connect to the system. But more importantly, the 796 (although SkyView software will pass it through) isn't really an position source for ADS-B Out. What is the GPS DATA option in the transponder menu set to?

 

[GlennB]

Sorry about the delay; been away from the airport for a bit.

It's possible that the transponder position processing is discarding position updates that do not validate for some reason - we're not able to qualify all of the external non-certified possibilities that one could possibly connect to the system. But more importantly, the 796 (although SkyView software will pass it through) isn't really an position source for ADS-B Out. What is the GPS DATA option in the transponder menu set to?

It's "Dynon Skyview other".  That's the only one on the list which will give an "OK" prompt to show it's accepting data.

Other info, now that I have it to hand:

Skyview version 14.1.0.3674
Garmin 795 software version 5.00
Garmin data format "Aviation in / NMEA & VHF out" (also, the only option producing sentences the Skview will accept)
Skyview serial input format "Garmin Aera"

I realise the 795 is a non-certified source, but it all worked without a murmur, albeit broadcasting SIL=0, until the V.14 upgrade.  Now the transponder periodically complains of being starved for data for brief instances.  Even that wouldn't be a problem, as we are VFR-only, if at least the message could be disabled.

 

[Dynon]

So the latest SV version - 14.2.1 - has an update to the transponder that does address some aspects of ADS-B transmission. I can't say with confidence that it'll fix your issue, but it's a good first thing to try. Remember that updating the transponder is a separate operation AFTER you've updated you SkyView system software.

 

[GlennB]

That sounds encouraging, thanks.

I have to confess I may have avoided doing the transponder update last time around, as on a previous occasion this went badly and bricked the unit.  But I'll gird my loins and bring both modules up to date.