Merry Christmas... I was hoping to get some thoughts\ideas. I recently bought a plane with a Garmin GTX 335. I was flying it across the country and ATC told me that "my altitude stop reporting" and another controller asked me for my altitude and said it was "fluctuating and cannot be used for IFR.
I did some research by pulling all of the ADSB data and putting it into excel spreadsheets. It seems like it is impossible for the transponder to report any altitude ending in x600 or x900 feet. 600 feet, 900 feet, 1600 feet, 2600, 2900, 3600, 3900, 4600, 4900, 5600, etc all won't report out. A shop tried putting in a new ACK 30.5 altitude encoder but that did not help.
When flying I can see occa