Anyone know why my ADS-B test failed?

[Piloto]

1 minute ago, RobertE said:

What I've witnessed from my system is that as soon as I'm moving about 5 mph I start receiving signals.  I assume I'm sending them at that time as well.  From what has been said about the proper speed setting being 70% of Vso it sounds like mine is set way too low but I happen to like it.  It's handing to see while taxing what aircraft are in the vicinity.

I would think would be very beneficial to see traffic when on the ground at 0kts. Like when holding for take off on the run up area. You want to be aware of traffic landing at both ends of the runway at a uncontrolled field.

José

[JKeeth]

The ADS-B system must be receiving magnetic heading from a digital source (AHRS) in order to display traffic when stationary. Without mag heading, the system will use GPS track to determine the direction the aircraft is pointing, and track can't be determined if not moving. Therefore no traffic until taxing if magnetic heading is not available. 

[JohnB]

12 hours ago, JKeeth said:

What ADS-B out equipment do you have, and is the GPS providing the in-air and on-ground logic, or is that being done with an external airspeed or squat switch?

The reason the FAA's system failed the "in-air on ground test" is because your airplane was reporting that it was in air mode while sitting on the ground (duh!), and in my experience this tends to happen most often after landing rather than prior to take-off. If your airplane reported that you were still in-air after you taxied off the runway, then that would cause the failure of the "air on ground" test. Of course, this would only happen at an airport that has coverage from an ADS-B ground station. If no ground station coverage, then your ADS-B OUT will never be received into the ADS-B system and therefore not see the "air on ground" discrepancy.

Fixing this depends on the ADS-B system in your airplane. For the Lynx NGT-9000, for example, GPS groundspeed is used to determine when to go from air mode to ground mode, and the groundspeed value is configured into the unit during installation. If the groundspeed is set too low then your airplane could be outputting air mode while taxing after landing, and in that case, increasing the GPS groundspeed would be the corrective action. Generally, the GPS groundspeed setting should be 70% of Vso.

Very helpful all thanks Keeth! I have an Aivyne AXP 340, and a garmin GDL 88 as my ADSB in/out solution. GPS Position is through my GTN 750. I just found a Garmin service bulletin (Thanks Debbie!) that said the pilot should try all sorts of things like making sure you have 3D GPS before taxi (makes sense) and some other things like making sure you're on the centerline on runways (??) and taxiing at a fast walk speed only. At most of the airports Im in, after landing, you have to come to a complete stop and then wait for ground to clear you. Some sounds like busywork and finger pointing to blame us pilots to me, but some of them make sense so Ill make sure im doing them and see. Im wondering if ill get a pass if I let the FAA know that I'm not eligible for the rebate since I got my equipment before the rebate program started?