I solved the problem with the lack of altitude info. on the previous report, but still failed again today. I seem to be close to passing on this one.
Any suggestions as to what I should try next?
TIA
These NIC/NACv/NACp errors are normally caused by poor GPS data when there are no Baro Alt errors, and you no longer seem to have those.
Since the errors only occurred ~5% of the time on your 51 minute flight, it is probably not a software or installation error.
What we don't know from this data is whether the 5% failure was all at once (e.g. at the start of the flight before you had a good 3D Diff GPS fix) or sprinkled throughout the flight as would happen from maneuvering flight (causing antenna performance issues) or COM radio transmissions interfering with GPS reception and causing occasional low fix integrity.
The good folks from the FAA that provide these reports can also provide .kmz files that can be loaded into Google Earth which will show you, second-by-second, where along the flight your ADS-B output was non-compliant. You would have to specifically request this.
What I would do next would be to make another flight where you make sure and don't take off until the GPS navigator providing GPS data to your ADS-B Out transponder has a full 3D Diff fix. Throughout the flight, I would monitor the GPS status page for that navigator and make sure it is maintaining that 3D Diff fix and not occasionally downgrading during COM transmissions.
Not sure what kind of GPS source you are using, but this is what the GPS status page looks like on the GNX 375 I am using for all IFR GPS navigation and ADS-B In/Out.
If you get a clean report on this flight, then the 5% failure on this last flight was probably the result of either taking off before the GPS had a good fix, or cycling power on the GPS during flight which would have also resulted in failures of this type a small percentage of the flight.
If you don't get a clean report on this flight, and don't see GPS fix momentary downgrading when using the COM radio, I would request the .kmz data for the last flight and see what you can learn in Google Earth.
Steve