KeithO
Well-Known Member
So, yesterday afternoon was the final flight home of the Arion Lightning I purchased. Obviously the first long cross country under my ownership. I hired a local CFI to do the flight since my wife is still a student pilot. Overall everything went well on the flight. Performance was as expected, there were pretty severe headwinds on the way back to Michigan given that the winds had reversed from southerlies to northerlies bringing with them some cool air from the polar regions.
When the flight approached Toledo Class C airspace, the controller reported that the altimeter data on ADSB was very intermittant and to switch to mode A instead of mode C. On departure from Parkersburg WV and on previous test flights at that location ATC had never made any comment regarding problems with the reported altitude. Since I am not personally familiar with any of the avionics or ADSB hardware, I have been studying the manuals of the now approximately 15 year old transponder and the much newer ADSB system.
It seems to me that the Garmin transponder, while a mode C device, does not have a built in altitude encoder, it relies on an external encoding altimeter. It appears to me that the Dynon is the only instrument (other than a backup ASI) to be connected to the static port system. The pilot did not report any anomalies with the altimeter on the Dynon, so that suggests there must be a problem with the serial communication from the Dynon to the transponder, or elsewhere in the chain to the Echo so that the ADS-B transmitter is not getting good altimeter data.
I went to the FAA website and pulled a report on the ADS-B data for the flight and it reported a 70% error rate on the altimeter data. Some of the 70% could have been from the portion of the flight from Toledo to Jackson after the controller had him turn mode C off, but still there is obviously a problem. Has anyone had something similar happen ? I have a scope so I can look what the signals look like at the output of the Dynon and at the input on the Transponder. Obviously any loose connections would be the first catch - if any. I have to wonder if there is a way to read the Dynon output into a terminal on a laptop and see if it is broadcasting garbage ???
Thanks for the input...
When the flight approached Toledo Class C airspace, the controller reported that the altimeter data on ADSB was very intermittant and to switch to mode A instead of mode C. On departure from Parkersburg WV and on previous test flights at that location ATC had never made any comment regarding problems with the reported altitude. Since I am not personally familiar with any of the avionics or ADSB hardware, I have been studying the manuals of the now approximately 15 year old transponder and the much newer ADSB system.
It seems to me that the Garmin transponder, while a mode C device, does not have a built in altitude encoder, it relies on an external encoding altimeter. It appears to me that the Dynon is the only instrument (other than a backup ASI) to be connected to the static port system. The pilot did not report any anomalies with the altimeter on the Dynon, so that suggests there must be a problem with the serial communication from the Dynon to the transponder, or elsewhere in the chain to the Echo so that the ADS-B transmitter is not getting good altimeter data.
I went to the FAA website and pulled a report on the ADS-B data for the flight and it reported a 70% error rate on the altimeter data. Some of the 70% could have been from the portion of the flight from Toledo to Jackson after the controller had him turn mode C off, but still there is obviously a problem. Has anyone had something similar happen ? I have a scope so I can look what the signals look like at the output of the Dynon and at the input on the Transponder. Obviously any loose connections would be the first catch - if any. I have to wonder if there is a way to read the Dynon output into a terminal on a laptop and see if it is broadcasting garbage ???
Thanks for the input...