Well, that was surprising. I saw a helicopter icon in Louisiana, well out of range except for the highest of aircraft. Apparently TIS-B data, but this is the first time I’ve seen a lone helicopter appearing so far away. I watched it quickly fade away then pulled up flightradar24 to see if I could find it. The data at the bottom of the page:
T-KAUS2
SQUAWK
LATITUDE
31.3199
LONGITUDE
-92.5383
I guess T-KAUS2 is the source of the TIS-B broadcast. Anyway, the most unusual aspect of this to me is how the helicopter is all by itself. Usually, when I notice TIS-B data, there is a cluster of aircraft in a confined area that appear together.
Is that information I can glean from somewhere? Your parenthetical remark, by the way, doesn’t seem incompatible with my understanding of how TIS-B works. From what I just read on FAA.GOV, ADS-R is broadcast for a 15nm radius and +/- 5000 feet of the receiving aircraft, so I gather from that that the aircraft requesting the broadcast was likely within that distance of the helicopter. Wouldn’t that receiving aircraft have also been part of the data?
ADS-R is specifically a rebroadcast by a ground station of an ADS-B message on a different datalink - e.g. ingesting a 1090MHz ADS-B message and sending a 978MHz one, or vice versa. The ground station is just relaying info that the aircraft already provided in some form.
TIS-B is more general, it tells you about an aircraft but the source of that data might be radar, mlat, etc.
On 1090MHz you can distinguish them by looking at the CF value in the DF18 message. recent dump1090s will tell you about this via the “type” field in aircraft.json (e.g. this one would have reported “adsr_icao”)
I am not into the details of ADS but have an observation. My location is some 50 miles north of Alexandria and frequently track various military aircraft in the area. Most of the time they maintain a corroder only a few miles east of Alexandria and maintain either a near circular orbit or a long north south linear pattern from central Arkansas to west of Baton Rouge. Typically it will be E3 Sentry aircraft flying that area. Sometimes aircraft, serial 61-2666, which has been modified as an NC-135W to test systems and equipment will be in the area.
Sort of sketchy but perhaps the equipment operators are picking helicopters for relay purposes due to the fact that they fly slower than other aircraft and thus would be available for test over a longer period of time.
N424AE is Air Evac 100 based in Rayville. La just east of Monroe which would put its flight path almost directly under the typical area of operation of the above mentioned military area of operations.
