Why so many missing callsigns?

Why do so many aircraft not include their callsign with their ADS-B transmission? It looks like it’s mostly the regional that don’t have it. But I’ve found some mainline as well. Also, some airlines only send their flight number without the airline ICAO identifier. And once in a while I’ll see one with a callsign that includes their flight number and gate (like 1195B4) where 1195 is for AAL1195 and B4 is their arrival gate at PHL. Anyone have any idea why this may be?

It’s a US-specific thing. In Europe, 95%+ of aircraft have their ident set. I would guess that without a strong requirement to set it correctly like there is in Europe, it’s a low priority and so it doesn’t get fixed.

On a similar topic, my dump1090-fa web page shows ADSB flights in green highlight, MLAT in blue highlight, but what’s the story with all of the un-highlighted (white) flights that appear to have all their data?

White rows have no recent position; they might have never had a position (Mode S, no mlat) or they had a position in the past, but now you’re not hearing one (moved out of mlat coverage, or moved to a range where your receiver can still hear some messages, but not enough to get a pair of position messages)

Here in Europe we suffer from a shortage of available Mode 3/A codes (squawks) due to high traffic density. Therefore we have a Mode S standard code 1000 which may be used by several aircraft at the same time. In this case the identification has to be done via the callsign (Flight ID). As a consequence, the callsign has to be correct. Air Traffic Controllers complain immediately if the callsign is not transmitted correctly. Over the years we managed to educate the pilots accordingly. :smiley: