11 ms·

Transponder Landing System enables precision approaches at McMurdo in Antarctica

148 points by rmnwski 2y ago

computerdl 2y ago
How does the TLS work with multiple aircraft landing at once? With ILS, the signal broadcast is static but it seems like it will now be per aircraft.
- FireBeyond 2y ago
  I would expect that these runways are not high volume. Temporary/shifting/special needs.
  - chowells 2y ago
    This is about McMurdo. I'd be surprised if they ever had multiple flights landing at once.
    - FireBeyond 2y ago
      Exactly. I could see a 'convoy' of aircraft for a resupply, but I also expect even that might be just a few a day (because of weather and such, to avoid excessive aborts or returns due to weather or unloading delays).
- dweekly 2y ago
  The entire fleet qualified for McMurdo seems to be six planes and three helicopters, if I'm reading this right. https://www.usap.gov/sciencesupport/scienceplanningsummaries/2023_2024/airoperations.cfm https://www.usap.gov/sciencesupport/scienceplanningsummaries... I would guess it to be pretty rare that multiple aircraft would be on approach at once, and if so, I'd imagine one could hold at a distance to allow approaches to be serialized.
  - cozzyd 2y ago
    I've flown to/from McMurdo on a total of 4 types of planes... C-17, C130 (kiwi AF), L-100 (Safari, contracted by Italian antarctic program) and LC-130 (to/from pole).
    - enjaydee 2y ago
      What an experience! Can I ask your role in visiting?
      - cozzyd 2y ago
        Basically I work on experiments (balloons and in-ice) that are attempting to detect ultra high energy neutrinos interacting in ice sheets via radio.
        DiggyJohnson 2y ago
        This continues to be one of the cooler ongoing projects that produces significant, physical results. Good luck finding the special neutrinos!
- cameldrv 2y ago
  There are a few other airports that have this, and my understanding is that only one aircraft can do the approach at a time. If another plane tunes in the ILS they will see the localizer and glideslope indications for the other plane. I’m not sure how the TLS figures out what transponder to look at, I guess either the controller enters in the code of the plane on approach or there’s some reserved transponder code for the approach.
- phire 2y ago
  In theory, you can broadcast different signals on different frequencies, one per aircraft.
gte525u 2y ago
There a couple companies that make a DILS where the localizer and glideslope can be temporarily deployed. The intent is for emergency or short term use.
kylehotchkiss 2y ago
Year round aviation access to Antartica. Well Done! Every step towards McMurdo becoming a normal city despite its location seems like such an incredible accomplishment. Can this work at pole station too? I realize there's a lot of other considerations landing there in the winter (fuel freeze temp?) but the less isolated it becomes, the more science we can get.
- bigiain 2y ago
  I'm guessing there are a whole bunch of assumptions and simplifications in standard aviation practice around lat/long, GPS, and magnetic compasses - which all fail at the pole(s). I bet it's "quite exciting" to be a pilot trying to fly at the pole doing anything apart from flying straight and level right past. Your longitude readout becomes useless as the lines of longitude converge. Your GPS altitude becomes wildly inaccurate because the orbital inclinations of the constellation means they never get above 45 degrees or so from the horizon. Your compass is pretty much trying to point straight down (and at the magnetic pole which is some way apart from the rotational axis of the earth pole). And it's cold, likely very bad weather, the landscape make orienting yourself and even seeing upcoming mountains challenging, and you are a long long way from a safe landing spot and even further from any realistic help.
  - MobiusHorizons 2y ago
    I think a lot of aviation navigation is by named waypoints on charts. I am definitely not an expert, but I believe some of these would be visually identifiable in good weather, or even identified by radar transponders. Compas deviations would certainly be an issue, but I believe are important to account for even in much more populated areas. Aviation does use gps now, but many of the previous systems still exist and are quite clever. The ILS system this is based off of is such a system.
  - p_l 2y ago
    Flying over north pole became quite popular due to great circle routes going that way. use of GPS in civilian aviation actually came from compass getting confused during polar flight resulting in heading reversal. GPS satellites also supported polar operations from the start as the critical user needed flights over north pole. (this is one of those cases where typical map projections confuse people). That said, magnetic compass deviations are common all over the world due to things like iron ore veins, so maps have corrections available. GPS isn't used for altitude in aircraft in practice, it's too inprecise - barometric altimeter plus radar altimeter are the precise instruments for that.
polemic 2y ago
ICE31 in the air right now https://www.flightradar24.com/ICE31/36b2c5d5 https://www.flightradar24.com/ICE31/36b2c5d5
webnrrd2k 2y ago
Landing at McMurdo Station seems a lot like landing on a giant, slow-moving aircraft carrier. I wonder how similar their ILS is to the ILS used on navy aircraft carriers?
- phire 2y ago
  Aircraft carriers have two systems. The Instrument Carrier Landing System (ICLS) is basically just an upgraded version of the civilian ILS which they squashed down onto a ship. It broadcasts a beam of radio waves into the air and any aircraft can pick it up and follow the glide slope. There is also the Automatic Carrier Landing System (ACLS), which is roughly equivalent to this system. Radar receivers on the carrier are fed into a computer, which calculates the aircraft's position and transmits back commands back to the aircraft's autopilot. The cool part about this Transponder Landing System is that it doesn't require any equipment upgrades to the aircraft. An aircraft equiped with original ILS equipment from the 60s can use it.
  - DiggyJohnson 2y ago
    Adding for flavor and context: The ACLS is colloquially referred to as the "magic carpet", and we are now decades in to the classic disagreement about pilot skills versus automation. It's just in this case the consequence is splattering into the stern of a ship.
- lxgr 2y ago
  The glacier moves orders of magnitude slower than an aircraft carrier does, so I doubt that the TLS used does any comparable automatic adjustments. It's probably more than enough to periodically survey the runway and input that data manually.
mmaunder 2y ago
Wow that’s badass. It’s tempting to argue that a GPS based RNAV approach could have similar performance but this has several advantages: The ground based equipment dictates approach path with no updates to onboard approach databases on aircraft needed. RNAV can’t do curved approaches on a glide slope as far as I know. ILS minimums are generally slightly lower than LPV which is the RNAV approach type with lowest minimums. This supports older aircraft with ILS (localizer with glide slope) that don’t have a WAAS capable GPS. Edit: Also, using the Mode S transponder with precision approach radar instead of ADSB-out for the aircraft position means older planes without ADSB (because they don’t fly under a mode C veil) can be supported and it also means the base is trusting their equipment for the aircraft position rather than trusting an aircraft that potentially doesn’t have an SBAS GPS on board.
- turrican 2y ago
  RNAV RNP approaches can contain curved descents. They’re usually used in areas with high terrain but I don’t see why they couldn’t be used down here. LPV minimums seem to usually be very close to ILS minimums these days. That said, it’s always nice to have a ground-based alternative approach. I wonder if they have sustained issues with GPS this far south.
- MobiusHorizons 2y ago
  Would RNAV be able to handle the runway moving nontrivial distances? That seems to be one of the problems this solves.
  - lxgr 2y ago
    You'd have to update the approach plates and their digital version in the FMS's database occasionally, but that has to happen anyway, given that I believe almost all of them still use magnetic north as a reference. (Not sure if modern FMSes can store that data in true north format internally, but at least once the runway gets officially renamed I bet that requires an update.)
    - jeffcoat 2y ago
macintux 2y ago
Unsurprisingly, the challenges of getting to, living in, and managing infrastructure in Antarctica is a frequent theme of posts shared here. Some previous discussions of note: * How to Operate an Airport in Antarctica (also via flightradar24.com): https://news.ycombinator.com/item?id=26340384 https://news.ycombinator.com/item?id=26340384 (68 comments) * Nuclear Power at McMurdo Station, Antarctica: https://news.ycombinator.com/item?id=27549484 https://news.ycombinator.com/item?id=27549484 (192 comments) And perhaps my favorite blog, brr.fyi makes frequent appearances here. An example: * South Pole Water Infrastructure: https://news.ycombinator.com/item?id=40615530 https://news.ycombinator.com/item?id=40615530 (63 comments) For all Antarctica posts: https://brr.fyi/tags#south-pole https://brr.fyi/tags#south-pole
- 0xEF 2y ago
  Sadly, brr.fyi is done with the Antarctica stint and currently looking for another job.
  - ustad 2y ago
    I’m sure he won’t find it difficult to land another interesting job. I once emailed him and got a reply from the Antartica! Super cool.
zokier 2y ago
How they do aircraft positioning is the most interesting aspect here. The article says its multilateration, but I don't think it's quite the tradional simple multilat. Instead they are doing some cleverness with two angle of arrival detectors arranged perpendicularly, which feels novel? Found this random paper that has more details https://www.icasc.co/wp-content/uploads/2023/02/Application_of_the_Transponder_Landing_System_to_Achieve_Airport_Accessibility.pdf https://www.icasc.co/wp-content/uploads/2023/02/Application_...
standardUser 2y ago
Reminded me of a blog I stumbled upon by a woman who, just for kick, decided to work and live in Antarctica: https://wandereatwrite.com/how-i-got-paid-to-live-in-antarctica/ https://wandereatwrite.com/how-i-got-paid-to-live-in-antarct...
- butlike 2y ago
  This was a great read

148 points by rmnwski 2y ago

How does the TLS work with multiple aircraft landing at once? With ILS, the signal broadcast is static but it seems like it will now be per aircraft.

FireBeyond 2y ago
I would expect that these runways are not high volume. Temporary/shifting/special needs.
- chowells 2y ago
  This is about McMurdo. I'd be surprised if they ever had multiple flights landing at once.
  - FireBeyond 2y ago
    Exactly. I could see a 'convoy' of aircraft for a resupply, but I also expect even that might be just a few a day (because of weather and such, to avoid excessive aborts or returns due to weather or unloading delays).
dweekly 2y ago
The entire fleet qualified for McMurdo seems to be six planes and three helicopters, if I'm reading this right. https://www.usap.gov/sciencesupport/scienceplanningsummaries/2023_2024/airoperations.cfm https://www.usap.gov/sciencesupport/scienceplanningsummaries... I would guess it to be pretty rare that multiple aircraft would be on approach at once, and if so, I'd imagine one could hold at a distance to allow approaches to be serialized.
- cozzyd 2y ago
  I've flown to/from McMurdo on a total of 4 types of planes... C-17, C130 (kiwi AF), L-100 (Safari, contracted by Italian antarctic program) and LC-130 (to/from pole).
  - enjaydee 2y ago
    What an experience! Can I ask your role in visiting?
    - cozzyd 2y ago
      Basically I work on experiments (balloons and in-ice) that are attempting to detect ultra high energy neutrinos interacting in ice sheets via radio.
      - DiggyJohnson 2y ago
        This continues to be one of the cooler ongoing projects that produces significant, physical results. Good luck finding the special neutrinos!
cameldrv 2y ago
There are a few other airports that have this, and my understanding is that only one aircraft can do the approach at a time. If another plane tunes in the ILS they will see the localizer and glideslope indications for the other plane. I’m not sure how the TLS figures out what transponder to look at, I guess either the controller enters in the code of the plane on approach or there’s some reserved transponder code for the approach.
phire 2y ago
In theory, you can broadcast different signals on different frequencies, one per aircraft.

gte525u 2y ago

There a couple companies that make a DILS where the localizer and glideslope can be temporarily deployed. The intent is for emergency or short term use.

kylehotchkiss 2y ago

Year round aviation access to Antartica. Well Done! Every step towards McMurdo becoming a normal city despite its location seems like such an incredible accomplishment. Can this work at pole station too? I realize there's a lot of other considerations landing there in the winter (fuel freeze temp?) but the less isolated it becomes, the more science we can get.

bigiain 2y ago
I'm guessing there are a whole bunch of assumptions and simplifications in standard aviation practice around lat/long, GPS, and magnetic compasses - which all fail at the pole(s). I bet it's "quite exciting" to be a pilot trying to fly at the pole doing anything apart from flying straight and level right past. Your longitude readout becomes useless as the lines of longitude converge. Your GPS altitude becomes wildly inaccurate because the orbital inclinations of the constellation means they never get above 45 degrees or so from the horizon. Your compass is pretty much trying to point straight down (and at the magnetic pole which is some way apart from the rotational axis of the earth pole). And it's cold, likely very bad weather, the landscape make orienting yourself and even seeing upcoming mountains challenging, and you are a long long way from a safe landing spot and even further from any realistic help.
- MobiusHorizons 2y ago
  I think a lot of aviation navigation is by named waypoints on charts. I am definitely not an expert, but I believe some of these would be visually identifiable in good weather, or even identified by radar transponders. Compas deviations would certainly be an issue, but I believe are important to account for even in much more populated areas. Aviation does use gps now, but many of the previous systems still exist and are quite clever. The ILS system this is based off of is such a system.
- p_l 2y ago
  Flying over north pole became quite popular due to great circle routes going that way. use of GPS in civilian aviation actually came from compass getting confused during polar flight resulting in heading reversal. GPS satellites also supported polar operations from the start as the critical user needed flights over north pole. (this is one of those cases where typical map projections confuse people). That said, magnetic compass deviations are common all over the world due to things like iron ore veins, so maps have corrections available. GPS isn't used for altitude in aircraft in practice, it's too inprecise - barometric altimeter plus radar altimeter are the precise instruments for that.

polemic 2y ago

ICE31 in the air right now https://www.flightradar24.com/ICE31/36b2c5d5 https://www.flightradar24.com/ICE31/36b2c5d5

webnrrd2k 2y ago

Landing at McMurdo Station seems a lot like landing on a giant, slow-moving aircraft carrier. I wonder how similar their ILS is to the ILS used on navy aircraft carriers?

phire 2y ago
Aircraft carriers have two systems. The Instrument Carrier Landing System (ICLS) is basically just an upgraded version of the civilian ILS which they squashed down onto a ship. It broadcasts a beam of radio waves into the air and any aircraft can pick it up and follow the glide slope. There is also the Automatic Carrier Landing System (ACLS), which is roughly equivalent to this system. Radar receivers on the carrier are fed into a computer, which calculates the aircraft's position and transmits back commands back to the aircraft's autopilot. The cool part about this Transponder Landing System is that it doesn't require any equipment upgrades to the aircraft. An aircraft equiped with original ILS equipment from the 60s can use it.
- DiggyJohnson 2y ago
  Adding for flavor and context: The ACLS is colloquially referred to as the "magic carpet", and we are now decades in to the classic disagreement about pilot skills versus automation. It's just in this case the consequence is splattering into the stern of a ship.
lxgr 2y ago
The glacier moves orders of magnitude slower than an aircraft carrier does, so I doubt that the TLS used does any comparable automatic adjustments. It's probably more than enough to periodically survey the runway and input that data manually.

mmaunder 2y ago

Wow that’s badass. It’s tempting to argue that a GPS based RNAV approach could have similar performance but this has several advantages: The ground based equipment dictates approach path with no updates to onboard approach databases on aircraft needed. RNAV can’t do curved approaches on a glide slope as far as I know. ILS minimums are generally slightly lower than LPV which is the RNAV approach type with lowest minimums. This supports older aircraft with ILS (localizer with glide slope) that don’t have a WAAS capable GPS. Edit: Also, using the Mode S transponder with precision approach radar instead of ADSB-out for the aircraft position means older planes without ADSB (because they don’t fly under a mode C veil) can be supported and it also means the base is trusting their equipment for the aircraft position rather than trusting an aircraft that potentially doesn’t have an SBAS GPS on board.

turrican 2y ago
RNAV RNP approaches can contain curved descents. They’re usually used in areas with high terrain but I don’t see why they couldn’t be used down here. LPV minimums seem to usually be very close to ILS minimums these days. That said, it’s always nice to have a ground-based alternative approach. I wonder if they have sustained issues with GPS this far south.
MobiusHorizons 2y ago
Would RNAV be able to handle the runway moving nontrivial distances? That seems to be one of the problems this solves.
- lxgr 2y ago
  You'd have to update the approach plates and their digital version in the FMS's database occasionally, but that has to happen anyway, given that I believe almost all of them still use magnetic north as a reference. (Not sure if modern FMSes can store that data in true north format internally, but at least once the runway gets officially renamed I bet that requires an update.)
  - jeffcoat 2y ago

macintux 2y ago

Unsurprisingly, the challenges of getting to, living in, and managing infrastructure in Antarctica is a frequent theme of posts shared here. Some previous discussions of note: * How to Operate an Airport in Antarctica (also via flightradar24.com): https://news.ycombinator.com/item?id=26340384 https://news.ycombinator.com/item?id=26340384 (68 comments) * Nuclear Power at McMurdo Station, Antarctica: https://news.ycombinator.com/item?id=27549484 https://news.ycombinator.com/item?id=27549484 (192 comments) And perhaps my favorite blog, brr.fyi makes frequent appearances here. An example: * South Pole Water Infrastructure: https://news.ycombinator.com/item?id=40615530 https://news.ycombinator.com/item?id=40615530 (63 comments) For all Antarctica posts: https://brr.fyi/tags#south-pole https://brr.fyi/tags#south-pole

0xEF 2y ago
Sadly, brr.fyi is done with the Antarctica stint and currently looking for another job.
- ustad 2y ago
  I’m sure he won’t find it difficult to land another interesting job. I once emailed him and got a reply from the Antartica! Super cool.

zokier 2y ago

How they do aircraft positioning is the most interesting aspect here. The article says its multilateration, but I don't think it's quite the tradional simple multilat. Instead they are doing some cleverness with two angle of arrival detectors arranged perpendicularly, which feels novel? Found this random paper that has more details https://www.icasc.co/wp-content/uploads/2023/02/Application_of_the_Transponder_Landing_System_to_Achieve_Airport_Accessibility.pdf https://www.icasc.co/wp-content/uploads/2023/02/Application_...

standardUser 2y ago

Reminded me of a blog I stumbled upon by a woman who, just for kick, decided to work and live in Antarctica: https://wandereatwrite.com/how-i-got-paid-to-live-in-antarctica/ https://wandereatwrite.com/how-i-got-paid-to-live-in-antarct...

butlike 2y ago
This was a great read