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These "flight radar" sites work by tracking the ADS-B transponder data where the aircraft are actively broadcasting their position. This is used in civilian avi

These "flight radar" sites work by tracking the ADS-B transponder data where the aircraft are actively broadcasting their position. This is used in civilian aviation to be able to more accurately tell the position, altitude, speed, heading etc. of planes (and avoid confusing random echos from rain etc. with planes). If a military aircraft shows up on that, it's because they want to be seen, for example as a show of force. Once they don't want to be seen, they turn off their transponder, and disappear from those sites. Which is exactly what happened once SHTF in Ukraine.

rjsw 4y ago
> If a military aircraft shows up on that, it's because they want to be seen, for example as a show of force. There were B-52s doing orbits over Kabul during the evacuation with their transponders turned on.
- JumpCrisscross 4y ago
  > B-52s doing orbits over Kabul during the evacuation with their transponders turned on These transponders’ primary goal is preventing collisions. America never lost air superiority over Kabul. Keeping transponders on reduces the risk of collisions amid chaos at the cost of dialling up the non-existent risk of detection by Taliban SAMs.
  - dboreham 4y ago
    Based on my Dad having worked on such a thing in the early 1960s, surely they have encrypted/spread-spectrum versions of such things?
    - oneplane 4y ago
      Perhaps, but that doesn't help with collision avoidance if commercial and private craft in the area do not.
    - JumpCrisscross 4y ago
      > surely they have encrypted/spread-spectrum versions of such things? Kabul’s airspace was a mess of civilian and military planes [1][2]. You want the Spanish A310 to know it’s barrelling towards a Superfortress. [1] https://en.m.wikipedia.org/wiki/2021_Kabul_airlift https://en.m.wikipedia.org/wiki/2021_Kabul_airlift [2] https://twitter.com/defencegeek/status/1427012384502292480?s=21 https://twitter.com/defencegeek/status/1427012384502292480?s...
      - remarkEon 4y ago
        Perhaps related [1]. In this case, these transmitters would have prevented the collision. It may seem crazy, but a collision with a large military aircraft out in the middle of nowhere has happened before. >Neither aircraft was equipped with TCAS collision avoidance systems, and although both crews had filed a flight plan, the German aircraft was not in contact with Namibian air traffic control and controllers were unaware of its presence in Namibian airspace. Furthermore, the Tupolev was flying at the wrong altitude, according to its flight plan and to the semicircular rule. [1] https://en.wikipedia.org/wiki/1997_Namibia_mid-air_collision https://en.wikipedia.org/wiki/1997_Namibia_mid-air_collision
samwillis 4y ago
Flightradar24 and most other only ADSB based tracking sites filter out the majority of military flights (I beleve). ADSBExchange (https://globe.adsbexchange.com/ https://globe.adsbexchange.com/) on the other hand does not, they claim that if they have the data in the system it is public. And as you said, if the military don’t want to be seen they can just turn off their transmitters. I live near a number of RAF and US Air Force bases in the UK. As far as I can see all RAF flights are visible on ADSBExchange. However, we quite often have US F16s fly over and they quite often are not tracked. So either they have permission here in the UK to turn off their transmitters (not convinced), there is a signalling issue, or ADSBExchange are filtering some data. It does appear to only affect US Air Force flight here though…
- jsmith45 4y ago
  Yeah, filtering is one possibility. They could also be switching the transponder to Mode 3 (equivalent to civilian Mode C) which is not ADS-B compatible but would still show up on normal normal civil radar scopes. Or they can use some military only modes. Some of those could in theory be shown on civil scopes, but I'm not sure they actually are, while others like mode 4 or 5 cannot. But they could show up on the UK's military scopes, given nato intercompatibility. Another theoretical option would be for the air force planes to be using mode-S, but having disabled mode-S extended squitter (which means the planes don't periodically broadcast their location, but simply only reply when interrogated by radar). I would expect ADS-B receiver to pick up on these periodic interrogations though. I'm not sure if interrogation responses are directional, but even if so, some receivers would probably be in the general direction of the radar site. Its not really clear which. Outside of wartime, normal US Air Force policy is to fully integrate into the civil ATC system, except in special military use/training areas or certain special missions. This integration just makes things safer for everybody.
- manicdee 4y ago
  They have to set the IFF system to the OFF position.

rjsw 4y ago

> If a military aircraft shows up on that, it's because they want to be seen, for example as a show of force. There were B-52s doing orbits over Kabul during the evacuation with their transponders turned on.

JumpCrisscross 4y ago
> B-52s doing orbits over Kabul during the evacuation with their transponders turned on These transponders’ primary goal is preventing collisions. America never lost air superiority over Kabul. Keeping transponders on reduces the risk of collisions amid chaos at the cost of dialling up the non-existent risk of detection by Taliban SAMs.
- dboreham 4y ago
  Based on my Dad having worked on such a thing in the early 1960s, surely they have encrypted/spread-spectrum versions of such things?
  - oneplane 4y ago
    Perhaps, but that doesn't help with collision avoidance if commercial and private craft in the area do not.
  - JumpCrisscross 4y ago
    > surely they have encrypted/spread-spectrum versions of such things? Kabul’s airspace was a mess of civilian and military planes [1][2]. You want the Spanish A310 to know it’s barrelling towards a Superfortress. [1] https://en.m.wikipedia.org/wiki/2021_Kabul_airlift https://en.m.wikipedia.org/wiki/2021_Kabul_airlift [2] https://twitter.com/defencegeek/status/1427012384502292480?s=21 https://twitter.com/defencegeek/status/1427012384502292480?s...
    - remarkEon 4y ago
      Perhaps related [1]. In this case, these transmitters would have prevented the collision. It may seem crazy, but a collision with a large military aircraft out in the middle of nowhere has happened before. >Neither aircraft was equipped with TCAS collision avoidance systems, and although both crews had filed a flight plan, the German aircraft was not in contact with Namibian air traffic control and controllers were unaware of its presence in Namibian airspace. Furthermore, the Tupolev was flying at the wrong altitude, according to its flight plan and to the semicircular rule. [1] https://en.wikipedia.org/wiki/1997_Namibia_mid-air_collision https://en.wikipedia.org/wiki/1997_Namibia_mid-air_collision

samwillis 4y ago

Flightradar24 and most other only ADSB based tracking sites filter out the majority of military flights (I beleve). ADSBExchange (https://globe.adsbexchange.com/ https://globe.adsbexchange.com/) on the other hand does not, they claim that if they have the data in the system it is public. And as you said, if the military don’t want to be seen they can just turn off their transmitters. I live near a number of RAF and US Air Force bases in the UK. As far as I can see all RAF flights are visible on ADSBExchange. However, we quite often have US F16s fly over and they quite often are not tracked. So either they have permission here in the UK to turn off their transmitters (not convinced), there is a signalling issue, or ADSBExchange are filtering some data. It does appear to only affect US Air Force flight here though…

jsmith45 4y ago
Yeah, filtering is one possibility. They could also be switching the transponder to Mode 3 (equivalent to civilian Mode C) which is not ADS-B compatible but would still show up on normal normal civil radar scopes. Or they can use some military only modes. Some of those could in theory be shown on civil scopes, but I'm not sure they actually are, while others like mode 4 or 5 cannot. But they could show up on the UK's military scopes, given nato intercompatibility. Another theoretical option would be for the air force planes to be using mode-S, but having disabled mode-S extended squitter (which means the planes don't periodically broadcast their location, but simply only reply when interrogated by radar). I would expect ADS-B receiver to pick up on these periodic interrogations though. I'm not sure if interrogation responses are directional, but even if so, some receivers would probably be in the general direction of the radar site. Its not really clear which. Outside of wartime, normal US Air Force policy is to fully integrate into the civil ATC system, except in special military use/training areas or certain special missions. This integration just makes things safer for everybody.
manicdee 4y ago
They have to set the IFF system to the OFF position.