Two days ago I watched 4 prop planes flying in very close 2x2 formation fly directly over me(NYC area), https://19216801.onl/ https://routerlogin.uno/https://192168ll.link/ I immediately pulled up my PiAware, but they weren't reporting anything. Is that normal? What might have they been? Typically the only thing I don't pick up is military, but they looked more commercial.
4 single engine prop planes with no ADSB?
4 months later
Did you check adsbexchange.com?
You can even pull up a lot of military on that site such as C-17s, C-5s, even pulled up Air Force One either as 92-9000 or 82-8000, I have seen E-4s, E-3s etc, various helicopters. The only thing I haven't pulled up are pretty much fighter jets or bombers, although I did see a B-52 once on it.
If they were vintage aircraft without electrical, then they might not have ADSB nor would they have a transponder. However you said that they were in the NYC area, so they would have to have one or the other due to all the commercial airports around there. Unless they had some sort of special permission from the FAA since it was some sort of formation flight.
I have seen formations on flightradar24 only show one plane, but there is something where they combine all transponders to one plane since they are considered a flight of 4.
15 days later
Do you have dual antennas on your PiAware receiver? In the US, ADS-B data can be transmitted along with transponder data on 1090 MHz. ADS-B data can also be transmitted on 987 MHz.