4 ms·

It's unlikely, since about 98% of the Earth has transponder coverage, so you at least have position and what the aircraft think's it's altitude is, with pretty

by TylerE 4y ago

It's unlikely, since about 98% of the Earth has transponder coverage, so you at least have position and what the aircraft think's it's altitude is, with pretty good precision and sample rate. It's only in a few spots in the middle the ocean that this doesn't exist. This was also relevant in that Airbus crash from maybe 15 years ago between South America and Africa. This is not a problem on the main to/from North America routes because there are enough populated islands along the way (Iceland, Greenland, Hawaii, Guam, etc)

lxgr 4y ago
Not sure what exactly you mean by "transponder coverage", but if you mean primary or secondary surveillance radar, this is not true for most of the Atlantic or Pacific. Radar (both primary and secondary, i.e. transponders) as well as ADS-B require line-of-sight, and oceanic air traffic control has to make due without that, which means operating either via ADS-C (i.e. planes self-reporting their position, autonomously determined via GPS or inertial navigation, via satellite communications) or effectively dead reckoning, augmented by occasional position reports via HF radio, which is called procedural control: https://en.wikipedia.org/wiki/Procedural_control https://en.wikipedia.org/wiki/Procedural_control
- hallidave 4y ago
  Space-based ADS-B is now a thing. It is used for coverage of the north Atlantic. https://www.navcanada.ca/en/air-traffic/space-based-ads-b.aspx https://www.navcanada.ca/en/air-traffic/space-based-ads-b.as...
  - lxgr 4y ago
    Yes, but note how this press release is mostly explaining what this technology could eventually be used for. I'm not aware of any ACCs actually using it for oceanic control today or having made an announcement of planning to do so in the future. It's a very exciting technology, sure, but I think it's many years of testing and flawless operation as a secondary data source away from replacing ADS-C on oceanic routes.
_s 4y ago
I think closer to 80-90% of all landmass has "active" surveillance, with another 40-50% of sea / oceans. Most of the South Pacific / South Atlantic / Southern Ocean (Antarctic); a lot of the North Pacific / North Atlantic / Indian / Arctic outside of the major islands and direct routes has nearly no coverage.
- tjohns 4y ago
  I think even this number is high. 80-90% sounds about right for the mainland US and Europe, but definitely isn't true elsewhere. Canada probably has ~50% radar coverage, and oceans have essentially 0% once you're beyond line of sight from from the coast. (And this is if you're a jet flying at high altitude. If you're down where smaller aircraft fly, I can point to areas on the US west coast that don't have radar or radio coverage. Heck, there's parts of the mainland US that don't even have NEXRAD weather radar coverage.)
  - rootusrootus 4y ago
    > Heck, there's parts of the mainland US that don't even have NEXRAD weather radar coverage. Is that a good comparison, though? It seems like NOAA funding for the NEXRAD sites is perpetually inadequate. The one in Portland occasionally has outages that last a while. I would have guessed that civilian air control radar is better funded than NEXRAD, and military radar probably so well funded that every square inch of CONUS is covered by at least one.
    - tjohns 4y ago
      Domestic civilian and military radar is the same thing. It's (mostly) all managed by the FAA, and the military just gets a copy of the civilian radar feed as part of the Joint Surveillance System. [1] The limiting factor is geography. Radar coverage in the US is excellent, but the mountains out west make universal coverage hard, and there's some areas that just aren't cost effective to cover. At 40,000 MSL, yes, everything in the US is covered. Below 10,000 MSL though, there are definite gaps - especially in the mountainous west. It's just physics, the mountains block the signal, and filling in all the gaps is cost prohibitive. Instead, they just tell aircraft to fly higher if they want radar service. As for outages... ATC radar goes out all the time. You just never hear about it because they either switch to an adjacent, (slower) en-route radar site as part of CENRAP [2], or fall back to procedural control (voice position reports on the radio). Redundancy is baked into the system at many levels, both technical and human. [1]: https://en.wikipedia.org/wiki/Joint_Surveillance_System https://en.wikipedia.org/wiki/Joint_Surveillance_System [2]: https://aviation.stackexchange.com/questions/9464/what-is-cenrap https://aviation.stackexchange.com/questions/9464/what-is-ce...
tjohns 4y ago
That number can't be right. 98% of the earth doesn't have primary radar coverage, let alone secondary (transponder) coverage. ATC radar is line of sight. At an altitude of 40,000 feet, you're beyond the radio horizon and lose coverage after about 380 miles - and that's the theoretical best case. Oceanic air traffic control is primarily a non-radar environment, using procedural separation. Even over land, most of Canada (outside major cities and the airways between them) doesn't have radar coverage. There's a map showing the gaps here: http://ilanreich.com/Public_Pics/Alaska/Section%20One.htm http://ilanreich.com/Public_Pics/Alaska/Section%20One.htm (The military does have over-the-horizon radar, but that's mostly used for missile defense. OTH radar isn't used for air traffic control.)
- TylerE 4y ago
  The newer systems that have come online over the past decade or so (partially in response to 370) actually use the iridium satelites
  - lxgr 4y ago
    These systems are using ADS-B and are only designed for operational/informational purposes so far, as far as I know. They are not used for air traffic control or other safety-critical purposes.
    - phire 4y ago
      And for anyone who doesn't know; ADS-B is simply the aircraft voluntarily reporting its own GPS coordinates. So it's not going to help at all in a MH370 scenario.
      - lxgr 4y ago
        > ADS-B is simply the aircraft voluntarily reporting its own GPS coordinates True, but that is ultimately the case for all flights outside of primary radar coverage.
    - tjohns 4y ago
elromulous 4y ago
Are you referring to AirFrance 447? https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447
deleted 4y ago
[deleted]

by TylerE 4y ago

lxgr 4y ago

Not sure what exactly you mean by "transponder coverage", but if you mean primary or secondary surveillance radar, this is not true for most of the Atlantic or Pacific. Radar (both primary and secondary, i.e. transponders) as well as ADS-B require line-of-sight, and oceanic air traffic control has to make due without that, which means operating either via ADS-C (i.e. planes self-reporting their position, autonomously determined via GPS or inertial navigation, via satellite communications) or effectively dead reckoning, augmented by occasional position reports via HF radio, which is called procedural control: https://en.wikipedia.org/wiki/Procedural_control https://en.wikipedia.org/wiki/Procedural_control

hallidave 4y ago
Space-based ADS-B is now a thing. It is used for coverage of the north Atlantic. https://www.navcanada.ca/en/air-traffic/space-based-ads-b.aspx https://www.navcanada.ca/en/air-traffic/space-based-ads-b.as...
- lxgr 4y ago
  Yes, but note how this press release is mostly explaining what this technology could eventually be used for. I'm not aware of any ACCs actually using it for oceanic control today or having made an announcement of planning to do so in the future. It's a very exciting technology, sure, but I think it's many years of testing and flawless operation as a secondary data source away from replacing ADS-C on oceanic routes.

_s 4y ago

I think closer to 80-90% of all landmass has "active" surveillance, with another 40-50% of sea / oceans. Most of the South Pacific / South Atlantic / Southern Ocean (Antarctic); a lot of the North Pacific / North Atlantic / Indian / Arctic outside of the major islands and direct routes has nearly no coverage.

tjohns 4y ago
I think even this number is high. 80-90% sounds about right for the mainland US and Europe, but definitely isn't true elsewhere. Canada probably has ~50% radar coverage, and oceans have essentially 0% once you're beyond line of sight from from the coast. (And this is if you're a jet flying at high altitude. If you're down where smaller aircraft fly, I can point to areas on the US west coast that don't have radar or radio coverage. Heck, there's parts of the mainland US that don't even have NEXRAD weather radar coverage.)
- rootusrootus 4y ago
  > Heck, there's parts of the mainland US that don't even have NEXRAD weather radar coverage. Is that a good comparison, though? It seems like NOAA funding for the NEXRAD sites is perpetually inadequate. The one in Portland occasionally has outages that last a while. I would have guessed that civilian air control radar is better funded than NEXRAD, and military radar probably so well funded that every square inch of CONUS is covered by at least one.
  - tjohns 4y ago
    Domestic civilian and military radar is the same thing. It's (mostly) all managed by the FAA, and the military just gets a copy of the civilian radar feed as part of the Joint Surveillance System. [1] The limiting factor is geography. Radar coverage in the US is excellent, but the mountains out west make universal coverage hard, and there's some areas that just aren't cost effective to cover. At 40,000 MSL, yes, everything in the US is covered. Below 10,000 MSL though, there are definite gaps - especially in the mountainous west. It's just physics, the mountains block the signal, and filling in all the gaps is cost prohibitive. Instead, they just tell aircraft to fly higher if they want radar service. As for outages... ATC radar goes out all the time. You just never hear about it because they either switch to an adjacent, (slower) en-route radar site as part of CENRAP [2], or fall back to procedural control (voice position reports on the radio). Redundancy is baked into the system at many levels, both technical and human. [1]: https://en.wikipedia.org/wiki/Joint_Surveillance_System https://en.wikipedia.org/wiki/Joint_Surveillance_System [2]: https://aviation.stackexchange.com/questions/9464/what-is-cenrap https://aviation.stackexchange.com/questions/9464/what-is-ce...

tjohns 4y ago

That number can't be right. 98% of the earth doesn't have primary radar coverage, let alone secondary (transponder) coverage. ATC radar is line of sight. At an altitude of 40,000 feet, you're beyond the radio horizon and lose coverage after about 380 miles - and that's the theoretical best case. Oceanic air traffic control is primarily a non-radar environment, using procedural separation. Even over land, most of Canada (outside major cities and the airways between them) doesn't have radar coverage. There's a map showing the gaps here: http://ilanreich.com/Public_Pics/Alaska/Section%20One.htm http://ilanreich.com/Public_Pics/Alaska/Section%20One.htm (The military does have over-the-horizon radar, but that's mostly used for missile defense. OTH radar isn't used for air traffic control.)

TylerE 4y ago
The newer systems that have come online over the past decade or so (partially in response to 370) actually use the iridium satelites
- lxgr 4y ago
  These systems are using ADS-B and are only designed for operational/informational purposes so far, as far as I know. They are not used for air traffic control or other safety-critical purposes.
  - phire 4y ago
    And for anyone who doesn't know; ADS-B is simply the aircraft voluntarily reporting its own GPS coordinates. So it's not going to help at all in a MH370 scenario.
    - lxgr 4y ago
      > ADS-B is simply the aircraft voluntarily reporting its own GPS coordinates True, but that is ultimately the case for all flights outside of primary radar coverage.
  - tjohns 4y ago

elromulous 4y ago

Are you referring to AirFrance 447? https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447

deleted 4y ago

[deleted]