ADSBExchange links

• Helicopters w/ LADD [replay] (LADD = data is "blocked" by some services, but not all)
• Helicopters marked 'military' [replay]
• Helicopters marked 'PIA' [replay] (PIA, Privacy ICAO Address = a pseudonym)
• Helicopters located via multilateration (MLAT) [replay] (MLAT = not transmitting its location)

• all helicopters [replay]

https://www.reddit.com/r/chicago/comments/1ocer4w/did_you_just_hear_or_see_a_helicopter_a_guide_to/?sort=new

my spreadsheet