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There can be a bit more nuance to it than that. FlightRadar24 and other tracking sites do use ADS-B data broadcast by aircraft themselves, but they also use oth

There can be a bit more nuance to it than that. FlightRadar24 and other tracking sites do use ADS-B data broadcast by aircraft themselves, but they also use other information. There are other ways that aircraft that aren't broadcasting ADS-B can still show up on a map. 1. Mode S: Even if an aircraft isn't broadcasting its own position via ADS-B, if it's using Mode S its position can be multilaterated if you have a cooperating network of receivers (which is what FR24, ADS-B Exchange, etc. have). 2. TIS-B: An aircraft could be using Mode A/C, which generally can't even be multilaterated, or it could have its transponder turned off entirely and ATC can still use primary radar returns to broadcast a synthetic ADS-B-type target for safety, so that other nearby aircraft will see it show up on their traffic displays. The data won't tell you what aircraft it is, but you know where it is. And in fact, it's frequently possible for experienced observers to figure out what kind of aircraft it is and who's flying it based just on its track, speed, and altitude. I frequently see contacts on ADS-B Exchange in the Los Angeles area that are obviously fighters flying without ADS-B or Mode S, showing up as TIS-B. Military aircraft on sensitive operations can turn off their transponders, and I don't know if China uses TIS-B, but I just wanted to clarify that there is data besides ADS-B that gets used, and that a network of receivers has capabilities that a single receiver doesn't.

toomuchtodo 5y ago
Iridium also has ADS-B receivers onboard the latest satellites going up to enable global coverage, although I don’t have context as to data access and pricing. https://aireon.com/resources/overview-materials/its-just-ads-b/ https://aireon.com/resources/overview-materials/its-just-ads...
- andrepew 5y ago
  I believe for the satellites to pick you up you need ADS-B antenna diversity (an antenna on the top and bottom of the plane) which I don’t believe is very common yet because it has cost.
- papercrane 5y ago
  You can buy access to the data from FlightAware. I've never been in a position to see the pricing, though I'm sure it's expensive.
- sorenjan 5y ago
  They're visible on Flightradar24. Look at the north Atlantic, there's usually several of them at any time. The satellite sourced data uses blue icons on the map.
  - wiedehopf 5y ago
    That's not Aireon data but rather ADS-C which is just Iridium data link as far as i know.
    - sorenjan 5y ago
      No it's ADS-B receivers on satellites. https://www.flightradar24.com/blog/satellite-based-ads-b-data-now-available-to-all-flightradar24-users/ https://www.flightradar24.com/blog/satellite-based-ads-b-dat...
jjwiseman 5y ago
Kinda relevant: Here's a thread about a group of aircraft flying in the U.S. that were trying to hide their identities by using the FAA's "Privacy ICAO Address" (PIA) program. Under the PIA program, aircraft can broadcast ADS-B but they don't use their real registration info, so theoretically you're not supposed to be able to tie the aircraft to a person or company: https://twitter.com/lemonodor/status/1456377882582798338 https://twitter.com/lemonodor/status/1456377882582798338 But because it's still relatively rare for aircraft to use PIA, and even more rare for a group of several aircraft to use PIA and take off from the same airport and fly together, they attracted the attention of a few people on twitter who suddenly got very interested in these aircraft and who was flying them. People quickly figured out where the aircraft where flying to, and realized that airport had a public webcam. As the jets landed, people confirmed the tail numbers of these aircraft that were trying to fly under the radar, so to speak. The thread ends with the identity of the aircraft and their owner having been discovered, some hypotheses about the reason for the flight, figuring out which resort the passengers were staying at, and... the airport having apparently seen what was happening on twitter and sending someone out to put a plastic bag or something over the webcam to block everyone's view.
- easton 5y ago
  It seems like the money and time it would take to set that up would be way more than just buying everyone tickets on a commercial plane for that flight.
  - jfrunyon 5y ago
    Of course flying on a commercial plane would be cheaper. They aren't flying on private jets because it's cheaper, they do it because their shareholders are the ones paying for it and they don't want to sit next to a plebe.
    - dylan604 5y ago
      and the hassle of dealing with the public in an airport vs rolling right up to the private plane, getting on, taking off. The only thing easier is POTUS on Air Force One
omegalulw 5y ago
> Even if an aircraft isn't broadcasting its own position via ADS-B, if it's using Mode S its position can be multilaterated if you have a cooperating network of receivers (which is what FR24, ADS-B Exchange, etc. have). I am a total noob in this area (and in general) but from my cursory understanding of Mode S, you would still have to have an active transponder on the aircraft. Wouldn't a military aircraft that wants to hide it's location not output any radio signals (except narrowband directed signals if those are practical?).

toomuchtodo 5y ago

Iridium also has ADS-B receivers onboard the latest satellites going up to enable global coverage, although I don’t have context as to data access and pricing. https://aireon.com/resources/overview-materials/its-just-ads-b/ https://aireon.com/resources/overview-materials/its-just-ads...

andrepew 5y ago
I believe for the satellites to pick you up you need ADS-B antenna diversity (an antenna on the top and bottom of the plane) which I don’t believe is very common yet because it has cost.
papercrane 5y ago
You can buy access to the data from FlightAware. I've never been in a position to see the pricing, though I'm sure it's expensive.
sorenjan 5y ago
They're visible on Flightradar24. Look at the north Atlantic, there's usually several of them at any time. The satellite sourced data uses blue icons on the map.
- wiedehopf 5y ago
  That's not Aireon data but rather ADS-C which is just Iridium data link as far as i know.
  - sorenjan 5y ago
    No it's ADS-B receivers on satellites. https://www.flightradar24.com/blog/satellite-based-ads-b-data-now-available-to-all-flightradar24-users/ https://www.flightradar24.com/blog/satellite-based-ads-b-dat...

jjwiseman 5y ago

Kinda relevant: Here's a thread about a group of aircraft flying in the U.S. that were trying to hide their identities by using the FAA's "Privacy ICAO Address" (PIA) program. Under the PIA program, aircraft can broadcast ADS-B but they don't use their real registration info, so theoretically you're not supposed to be able to tie the aircraft to a person or company: https://twitter.com/lemonodor/status/1456377882582798338 https://twitter.com/lemonodor/status/1456377882582798338 But because it's still relatively rare for aircraft to use PIA, and even more rare for a group of several aircraft to use PIA and take off from the same airport and fly together, they attracted the attention of a few people on twitter who suddenly got very interested in these aircraft and who was flying them. People quickly figured out where the aircraft where flying to, and realized that airport had a public webcam. As the jets landed, people confirmed the tail numbers of these aircraft that were trying to fly under the radar, so to speak. The thread ends with the identity of the aircraft and their owner having been discovered, some hypotheses about the reason for the flight, figuring out which resort the passengers were staying at, and... the airport having apparently seen what was happening on twitter and sending someone out to put a plastic bag or something over the webcam to block everyone's view.

easton 5y ago
It seems like the money and time it would take to set that up would be way more than just buying everyone tickets on a commercial plane for that flight.
- jfrunyon 5y ago
  Of course flying on a commercial plane would be cheaper. They aren't flying on private jets because it's cheaper, they do it because their shareholders are the ones paying for it and they don't want to sit next to a plebe.
  - dylan604 5y ago
    and the hassle of dealing with the public in an airport vs rolling right up to the private plane, getting on, taking off. The only thing easier is POTUS on Air Force One

omegalulw 5y ago

> Even if an aircraft isn't broadcasting its own position via ADS-B, if it's using Mode S its position can be multilaterated if you have a cooperating network of receivers (which is what FR24, ADS-B Exchange, etc. have). I am a total noob in this area (and in general) but from my cursory understanding of Mode S, you would still have to have an active transponder on the aircraft. Wouldn't a military aircraft that wants to hide it's location not output any radio signals (except narrowband directed signals if those are practical?).