7 ms·

VORs are pretty interesting. At first i thought every plane had a small antenna array on board to check the direction to the VOR. But the direction is just cal

VORs are pretty interesting. At first i thought every plane had a small antenna array on board to check the direction to the VOR. But the direction is just calculated by the phase shift between an omnidirectional and a directional signal. So it can be implemented very cheaply on every plane.

VBprogrammer 2y ago
ADF uses radio direction finding techniques. It's not very accurate and is all but deprecated except for some corner cases where the legislation hasn't yet allowed for overlay approaches (replacing a real radio beacon with its true position via GPS / IRS). There are some convincing reasons for being cautious on general on that front. Accidents have happened because some beacons have been substituted for the wrong location or even things like slant range being different from true range. In general ADF is so inaccurate that its protected areas are massive.
- aftbit 2y ago
  There's also a very real chance that commercial aviation may find itself operating in a GPS-denied environment, at least in various edge cases. For example, combat zones often employ GPS spoofing and jamming, and because radio waves don't exactly respect borders, this can sometimes affect civilian equipment outside of the combat zone. This has happened at least near Israel, Iraq, and Ukraine in the last few years. In other cases, truckers or rideshare drivers that want to spoof their company trackers end up parking too close to an airport and impacting planes on an RNAV approach.
  - ryandrake 2y ago
    > There's also a very real chance that commercial aviation may find itself operating in a GPS-denied environment, at least in various edge cases. Yea, it's kind of terrifying that we are slowly putting all of our eggs in the GPS basket. I love GPS but when lives are at stake, you need a redundant backup navigation system that is robustly deployed and reliably works.
    - ammar2 2y ago
      The VOR Minimum Operation Network[1] in the US is basically supposed to be that. They're decommissioning a lot of the VORs but at least guaranteeing that you'll be 100NM away from a working VOR and an airport with an approach that can be accomplished with VORs for the initial fixes. Still definitely feels like putting a lot of reliance on GPS but at least there's a backup for the worst case. [1] https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gbng/vormon https://www.faa.gov/about/office_org/headquarters_offices/at...
      - tjohns 2y ago
        There's also a DME Minimum Operational Network, for airliners that can use DME-DME RNAV. (That's too expensive for smaller aircraft to install, though.)
        cameldrv 2y ago
        It's too bad that DME/DME RNAV isn't more widely available. The only real reason it's so expensive is that there isn't much demand for it since GPS (usually) works fine. Electronics-wise, it's not much more complicated than a transponder. Unlike a GPS, it does have to transmit, so it will always be somewhat more expensive than GPS. The other problem is that there's a limit to how many aircraft a DME station can serve at a time (about 100), but I believe that could be greatly expanded if aircraft weren't pinging the DME so often. A position fix every second is generally fine, and it could be even more infrequent if you have a cheap inertial system to fuse with it that can fill in the track for a few seconds between pings.
        rlpb 2y ago
        One thing I have yet to understand is why DME-DME is preferred over VOR-VOR. Because the latter can support unlimited aircraft, unlike DME.
        chipsa 2y ago
        Probably the required accuracy. VOR is on the order of a degree for accuracy. DME is around 0.1nm. So if you’re 50nm from the VOR, then you may have a position fix error of 0.87nm across the radial, if I did my math right.
  - _djo_ 2y ago
    It's currently happening in the Eastern DRC too, affecting not only scheduled commercial traffic but humanitarian flights as well.
  - Scoundreller 2y ago
    I'm wondering if there's some doppler-shift assessment possible to detect (and possibly reject) spoofing/jamming? A fixed ground-based spoofer/jammer will be too consistent in its doppler-shift, unless it varies its frequency slightly, but that would only work well against specific targets, not broad areas. > Radio waves experience Doppler shifts the same as sound waves do as objects move. The Doppler shifts for the real satellites will all be different as the object moves either towards or away from them depending on their position in the sky. However, the Doppler shift caused by the object’s motion due to a spoofer is the same for all the satellites signals because they are all arriving from the same direction. This uniformity of Doppler is another indication of spoofing. Again, only the most sophisticated spoofer can account for an object’s motion to adjust its Doppler shift for each individual satellite, and to do so requires tracking the object’s course. https://safran-navigation-timing.com/resiliency-in-pnt-gps-gnss-jamming-and-spoofing/ https://safran-navigation-timing.com/resiliency-in-pnt-gps-g...
    - cjrp 2y ago
      I’m not sure if they still use it, but there was an Inertial Reference System on board - you set your location at the start of the flight, and then it can (roughly) give you a position using dead reckoning. A large disagreement between this position and the GPS position would result in an alert.
      - Scoundreller 2y ago
        Definitely still a thing and I think that’s the goto when GPS fails. Of course there’s drift that accumulates. I think the primary threat to commercial aviation without GPS is guided landing systems where you need the location precision.
  - scoopr 2y ago
    Not just near battlezones, just being near a jammy neighbour is enough: https://yle.fi/a/74-20086338 https://yle.fi/a/74-20086338
- tjohns 2y ago
  NDBs/ADF are much more common outside the US, where there isn't a huge installed VOR network or where there is a need for long-range airways over remote terrain. (Canada, I'm looking at you.)
- mschuster91 2y ago
  > replacing a real radio beacon with its true position via GPS / IRS That's the last thing you want to do. Here in Europe, we're dealing with serious issues because the Russians are jamming GPS from somewhere in Kaliningrad, but unfortunately we can't respond adequately without legitimately risking WW3. [1] https://www.bbc.com/news/articles/cne900k4wvjo https://www.bbc.com/news/articles/cne900k4wvjo
  - actionfromafar 2y ago
    Depends on what you mean adequately. We probably shouldn't carpet bomb them. But there's a lot more that could be done - turning the weapons donations to Ukraine from a drip-drip of the spigot to a firehose should wrap the war up.
- Scoundreller 2y ago
  > In general ADF is so inaccurate that its protected areas are massive Great for listening to LW & MW(AM) radio stations in the cockpit though. Rumour has it some pilots would patch big sports games into the in-flight entertainment channels so you wouldn't miss them just because you're in the air.
jojobas 2y ago
Easiest to understand with a flashing + rotating light analogy. When a rotating, say one turn in 10 seconds, green light is pointing north, a red light flashes. If you see a green flash 1 second before a red flash, you're on the 36 degree radial.
- platz 2y ago
  Wouldn't you be on the 324 degree radial
  - lisper 2y ago
    Depends on the direction of rotation which the GP didn’t specify.
0xfaded 2y ago
Here is the authoritative video of an English radio engineer explaining how VOR works. It truly is 60s level wizardry. https://youtu.be/tZ2gG1v9Xg8 https://youtu.be/tZ2gG1v9Xg8

VBprogrammer 2y ago

ADF uses radio direction finding techniques. It's not very accurate and is all but deprecated except for some corner cases where the legislation hasn't yet allowed for overlay approaches (replacing a real radio beacon with its true position via GPS / IRS). There are some convincing reasons for being cautious on general on that front. Accidents have happened because some beacons have been substituted for the wrong location or even things like slant range being different from true range. In general ADF is so inaccurate that its protected areas are massive.

aftbit 2y ago
There's also a very real chance that commercial aviation may find itself operating in a GPS-denied environment, at least in various edge cases. For example, combat zones often employ GPS spoofing and jamming, and because radio waves don't exactly respect borders, this can sometimes affect civilian equipment outside of the combat zone. This has happened at least near Israel, Iraq, and Ukraine in the last few years. In other cases, truckers or rideshare drivers that want to spoof their company trackers end up parking too close to an airport and impacting planes on an RNAV approach.
- ryandrake 2y ago
  > There's also a very real chance that commercial aviation may find itself operating in a GPS-denied environment, at least in various edge cases. Yea, it's kind of terrifying that we are slowly putting all of our eggs in the GPS basket. I love GPS but when lives are at stake, you need a redundant backup navigation system that is robustly deployed and reliably works.
  - ammar2 2y ago
    The VOR Minimum Operation Network[1] in the US is basically supposed to be that. They're decommissioning a lot of the VORs but at least guaranteeing that you'll be 100NM away from a working VOR and an airport with an approach that can be accomplished with VORs for the initial fixes. Still definitely feels like putting a lot of reliance on GPS but at least there's a backup for the worst case. [1] https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gbng/vormon https://www.faa.gov/about/office_org/headquarters_offices/at...
    - tjohns 2y ago
      There's also a DME Minimum Operational Network, for airliners that can use DME-DME RNAV. (That's too expensive for smaller aircraft to install, though.)
      - cameldrv 2y ago
        It's too bad that DME/DME RNAV isn't more widely available. The only real reason it's so expensive is that there isn't much demand for it since GPS (usually) works fine. Electronics-wise, it's not much more complicated than a transponder. Unlike a GPS, it does have to transmit, so it will always be somewhat more expensive than GPS. The other problem is that there's a limit to how many aircraft a DME station can serve at a time (about 100), but I believe that could be greatly expanded if aircraft weren't pinging the DME so often. A position fix every second is generally fine, and it could be even more infrequent if you have a cheap inertial system to fuse with it that can fill in the track for a few seconds between pings.
      - rlpb 2y ago
        One thing I have yet to understand is why DME-DME is preferred over VOR-VOR. Because the latter can support unlimited aircraft, unlike DME.
        chipsa 2y ago
        Probably the required accuracy. VOR is on the order of a degree for accuracy. DME is around 0.1nm. So if you’re 50nm from the VOR, then you may have a position fix error of 0.87nm across the radial, if I did my math right.
- _djo_ 2y ago
  It's currently happening in the Eastern DRC too, affecting not only scheduled commercial traffic but humanitarian flights as well.
- Scoundreller 2y ago
  I'm wondering if there's some doppler-shift assessment possible to detect (and possibly reject) spoofing/jamming? A fixed ground-based spoofer/jammer will be too consistent in its doppler-shift, unless it varies its frequency slightly, but that would only work well against specific targets, not broad areas. > Radio waves experience Doppler shifts the same as sound waves do as objects move. The Doppler shifts for the real satellites will all be different as the object moves either towards or away from them depending on their position in the sky. However, the Doppler shift caused by the object’s motion due to a spoofer is the same for all the satellites signals because they are all arriving from the same direction. This uniformity of Doppler is another indication of spoofing. Again, only the most sophisticated spoofer can account for an object’s motion to adjust its Doppler shift for each individual satellite, and to do so requires tracking the object’s course. https://safran-navigation-timing.com/resiliency-in-pnt-gps-gnss-jamming-and-spoofing/ https://safran-navigation-timing.com/resiliency-in-pnt-gps-g...
  - cjrp 2y ago
    I’m not sure if they still use it, but there was an Inertial Reference System on board - you set your location at the start of the flight, and then it can (roughly) give you a position using dead reckoning. A large disagreement between this position and the GPS position would result in an alert.
    - Scoundreller 2y ago
      Definitely still a thing and I think that’s the goto when GPS fails. Of course there’s drift that accumulates. I think the primary threat to commercial aviation without GPS is guided landing systems where you need the location precision.
- scoopr 2y ago
  Not just near battlezones, just being near a jammy neighbour is enough: https://yle.fi/a/74-20086338 https://yle.fi/a/74-20086338
tjohns 2y ago
NDBs/ADF are much more common outside the US, where there isn't a huge installed VOR network or where there is a need for long-range airways over remote terrain. (Canada, I'm looking at you.)
mschuster91 2y ago
> replacing a real radio beacon with its true position via GPS / IRS That's the last thing you want to do. Here in Europe, we're dealing with serious issues because the Russians are jamming GPS from somewhere in Kaliningrad, but unfortunately we can't respond adequately without legitimately risking WW3. [1] https://www.bbc.com/news/articles/cne900k4wvjo https://www.bbc.com/news/articles/cne900k4wvjo
- actionfromafar 2y ago
  Depends on what you mean adequately. We probably shouldn't carpet bomb them. But there's a lot more that could be done - turning the weapons donations to Ukraine from a drip-drip of the spigot to a firehose should wrap the war up.
Scoundreller 2y ago
> In general ADF is so inaccurate that its protected areas are massive Great for listening to LW & MW(AM) radio stations in the cockpit though. Rumour has it some pilots would patch big sports games into the in-flight entertainment channels so you wouldn't miss them just because you're in the air.

jojobas 2y ago

Easiest to understand with a flashing + rotating light analogy. When a rotating, say one turn in 10 seconds, green light is pointing north, a red light flashes. If you see a green flash 1 second before a red flash, you're on the 36 degree radial.

platz 2y ago
Wouldn't you be on the 324 degree radial
- lisper 2y ago
  Depends on the direction of rotation which the GP didn’t specify.

0xfaded 2y ago

Here is the authoritative video of an English radio engineer explaining how VOR works. It truly is 60s level wizardry. https://youtu.be/tZ2gG1v9Xg8 https://youtu.be/tZ2gG1v9Xg8