I see these “bad” hexcodes quite a bit from my KFUL site (Only 24nm from KLAX). I saw them in the list of a/c with dump1090, but never had positions showing for them. dump1090-mutability does give me their positions.
So, if I understand TIS-B… these “bad” hexcodes are non-adsb a/c that have their positions broadcasted via ads-b ground stations to ads-b equipped a/c. The TIS-B info seems to stay fairly persistent with my KFUL site, but does drop off from time to time. I have not watched it long enough to see if there is some pattern. My KCNO site pics up the info occasionally, but I have hills between the KCNO and KFUL site that I am sure is blocking the ads-b ground station broadcasting this info.
I just noticed the TIS-B info drop off for about a minute or two. When it did come back, my a/c count went up by about 70-80.
It would be great if the real hexcodes could be determined. However, if not, can these a/c be colored differently on the map to indicate that they are TIS-B a/c?
Here is a track of what appears to the a police helicopter that departed from KLGB and did a few orbits and is patrolling.
The ‘beehive’ around KLAX when I am reeving TIS-B