What could cause multiple aircraft to disappear?


#1

I live right next to PHL so I pick up most aircraft on the ground there. Once in a while all signals will drop out for a few seconds, or even a couple of minutes. I finally was able to capture this phenomenon that might help explain better what I mean. (Note: yes this is dump1090-fa, with modified code, so it looks quite different than the original). The two screenshots were taken only seconds apart. The pink ones show stale data, the bright red is live data. So every aircraft was there initially (not shown) and then eventually they all went stale (almost at the exact same time). Then they came back up all at the same time.

What could be causing this? Surely I couldn’t be losing all those signals at once and then gaining them back at the same time. Or could I? Is dump1090 just not able to process the data for a period of time? Any ideas?

Thanks,
Huff


#2

Image link is broken (edit: working now) but that sounds like TIS-B behaviour

(the TIS-B implementation I’ve seen seems to send out positions infrequently in batches; the interval between batches can be quite long, especially if there are not consistenly aircraft requesting TIS-B)