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Comment by fergbrain | Hacker News Reader

“Every civilian airliner is equipped with a special device — the so-caller ADS-B (Automatic Dependent Surveillance-Broadcast) transponder”

Not true actually: in the US, ADS-B isn’t required until January 1, 2020 [1].

Also, FR24 uses radar data in the US (probably because not all aircraft has ADS-B) [2].

There are also sites, such as ADS-B Exchange [3] that provide unfiltered flight data...very helpful for tracking military flights and such.

[1] https://www.faa.gov/nextgen/programs/adsb/faq/#g2

[2] https://www.flightradar24.com/how-it-works

[3] https://www.adsbexchange.com

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Even after 2020 ADS-B out won't be required in much of the airspace in the US. Only within 30 nautical miles of a class B airport, within the lateral limits of a class C airport, within class D airspace, and above 10k feet (but not below 2500 AGL I think). Even then, its only required for aircraft originally equipped with an alternator and electrical system (except in class B).

Basically, it's optional in most uncontrolled airspace and for older aircraft.

In practice, anything that can be described as an "airliner" is a large commercial aircraft and flies above 10k regularly. Probably required to have ADS-B.

Oh whoops, I misread as "airplane"

AU: Another good example where it'd pay off to use the 'FQDN', transport category aircraft.

To be fair, that's going to include the vast majority of aircraft. Most people will be above 2500AGL if they're not flying for very short distances. That said, there's always people that just like to fly in an unsafe manner.

Sorry, I may have worded that confusingly. The important number is 10,000 MSL. If you don't go above that you don't need ADS-B (as long as you stay out of the other airspace mentioned). They make an exception for people flying around high terrain, so if you are above 10,000 MSL but below 2,500 AGL then you are also exempt.

What is "uncontrolled airspace"?

https://en.wikipedia.org/wiki/Uncontrolled_airspace

Flightaware hardware will perform multilateration (using time distance of arrival) for transponders not announcing location via ADS-B.

https://flightaware.com/adsb/mlat/

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