GLS approaches: when do you think this will be available for GA?

[Lunar Module]

Newbie question. I have been studying for the IFR written exam and just learned about the FAA's NextGeneration plans for developing localized GLS systems as the next step in precision landing guidance technology. Sounds very cool. From what I can tell, a WAAS/SBAS capable navigator will not be capable of using GLS data when it becomes widely available and use of these systems will require new GPS hardware, buy I may be wrong about this. Google/AI is not terribly helpful and doesn't seem to differentiate WAAS/SBAS from local GBAS capability. WAAS GPS units are not inexpensive and if they will need to eventually be replaced with GLS capable units it might make sense to hold off getting one right now unless GLS is far off in the future. So I am wondering if any of you have an opinion on how soon we might see GLS equipment at airports and GLS capable GPS navigators available for the GA market? I imagine that this is probably years off in the future, but I just want to confirm this guess. Thanks very much.

 

[tsts4]

I’m missing something. What’s the benefit of GBAS over WAAS GPS? Almost seems like a different name for the same thing.

 

[Lunar Module]

There is some confusing terminology relating to these systems. Perhaps I don't understand it. GBAS just means "ground based augmentation system" and WAAS is a kind of GBAS, but I think the NextGen system is using the term GBAS differently and in a more specific manner. If you look at the Garmin website, they indicate that their WAAS units are also SBAS (satellite based augmentation system) capable, but they don't make any reference to Next Gen GBAS capability. And I read somewhere that NextGen GBAS receivers don't use frequencies but rely on "Channels", whatever that means.

As I understand it, the NextGen GBAS systems are LOCAL to each airport and not dependent upon the WAAS ground stations. They take satellite data and then provide the increased resolution that WAAS provides but do so locally. If the WAAS system were to go down I think the local GBAS systems would remain operational. And they have an accuracy of 1m in horizontal and vertical resolution, which is even better than WAAS.

 

[pdonahue]

I think that GBAS uses highly localized GPS corrections where WAAS uses less localized correction and is therefore less accurate. But do I need something that's more accurate than 1 meter? Will they let me shoot an approach below 200' if I have GBAS? Is this going to be like MLS, promised but never delivered?

 

[Lunar Module]

Here is a link to a brief description of GBAS (GLS). It is in use in a few locations and it already installed on some commercial airliners.

https://skybrary.aero/articles/gbas-landing-system-gls

And here is a YouTube video showing a simulated GLS approach into Bremen:

 

[Lunar Module]

I think that GBAS uses highly localized GPS corrections where WAAS uses less localized correction and is therefore less accurate. But do I need something that's more accurate than 1 meter? Will they let me shoot an approach below 200' if I have GBAS? Is this going to be like MLS, promised but never delivered?

Apparently with the right equipment and training you can shoot a Cat III landing with this system. I wonder if they might be able to lower minimums when/if these systems become more widely available? Probably not, but interesting to think about it anyway.

 

[Roller]

I can’t even shoot a LPV at our airline
I have no XM type big picture weather data

In many cases GA tends to be much more advanced than airlines

Apparently with the right equipment and training you can shoot a Cat III landing with this system. I wonder if they might be able to lower minimums when/if these systems become more widely available? Probably not, but interesting to think about it anyway.

Uhh

 

[tsts4]

I dunno. Doesn’t seem like something that’s going to be adopted in the US anytime soon to me.

 

[Lunar Module]

I can’t even shoot a LPV at our airline
I have no XM type big picture weather data

In many cases GA tends to be much more advanced than

Wow. I didn’t realize that. I guess the older technology works pretty well. But still….

 

[Roller]

Wow. I didn’t realize that. I guess the older technology works pretty well. But still….

It’s not the tech, we have full WAAS

 

[RussR]

There are GLS approaches at only 3 airports in the U.S. - EWR, IAH, and SFO. The minimums for these approaches, as of right now, are identical to the LPV minimums on the RNAV (GPS) approaches to the same runway.

Of course this may change in the future. But if you're looking to buy a GPS unit now, I certainly wouldn't be putting it off waiting for GLS approaches. It may be a very long time.

For clarification, SBAS is Space Based Augmentation System. The US WAAS is a type of SBAS, although there are others (like Europe's EGNOS). GBAS is Ground Based Augmentation System, of which LAAS is just the US's implementation of it.

 

[cailloux]

There are GLS approaches at only 3 airports in the U.S. - EWR, IAH, and SFO. The minimums for these approaches, as of right now, are identical to the LPV minimums on the RNAV (GPS) approaches to the same runway.

Those are United (ex-Continental) hubs, and my recollection is that they were the only interested party in studying ground-based augmentation instead of WAAS and/or being content with ILS. It was the early days of GPS when my minimums on a GPS approach were identical to (or higher than) the minimums on an NDB approach... If you look at the FAA's own website, it's basically dead with no new information for several years: https://laas.tc.faa.gov/

Given the success and lower cost of GPS/RNAV approaches for equipment maintenance and approach design, and the relative performance, I would be surprised if GLS/GBAS/LAAS is built out any further. New development for NextGen in the RNAV world is building out DME-only facilities for DME/DME-RNAV, which is mainly the domain of Transport Category aircraft.

My only caveat is that a newer generation of WAAS receivers may come out which will enable GPS/RNAV-based Precision Approaches. That requires alerting to a degredation of signal integrity within 6.0 seconds, and GPS currently alerts at 6.2 seconds. (Yes, a whopping 0.2 seconds between ICAO Annex 10, Volume 1, Chapter 3, Section 7 requirements for a Precision Approach and the system design for LPV and LPV200 approaches, to consider them "Precision.")

 

[Lunar Module]

There are GLS approaches at only 3 airports in the U.S. - EWR, IAH, and SFO. The minimums for these approaches, as of right now, are identical to the LPV minimums on the RNAV (GPS) approaches to the same runway.

Of course this may change in the future. But if you're looking to buy a GPS unit now, I certainly wouldn't be putting it off waiting for GLS approaches. It may be a very long time.

For clarification, SBAS is Space Based Augmentation System. The US WAAS is a type of SBAS, although there are others (like Europe's EGNOS). GBAS is Ground Based Augmentation System, of which LAAS is just the US's implementation of it.

Thanks. I'm getting the definite impression that this isn't a technology that will be widely implemented any time soon (if ever). From a bit more poking around I did last night, it seems as though the major advantage it offers would be for very busy airports with certain challenging configurations (like SFO) where the GLS approaches could be used to increase traffic throughput during IMC conditions compared to ILS (or even WAAS) approaches. I'm not sure that it offers a lot to less busy airports where WAAS and ILS approaches are

Also, I went to the FAA website relating to Next Generation planning and it seems that GBAS isn't even on their radar any more. It seems to have disappeared from their agenda a few years ago. That web site linked to a very detailed report from a consortium of airlines (United being the most involved) and the FAA presenting a trial of GBAS that they performed at SFO back in 2016 that was kind of interesting. They were very happy with the results they got (tighter patterns in IMC) but that was the last thing I could find. So I guess its a dead end.

Thanks for the info. You guys really know your stuff. Now I can focus my attention on whether it's time to dump ILS/VOR and go strictly GPS based or not when planning a future avionics upgrade. Never a dull moment!

 

[Lunar Module]

Those are United (ex-Continental) hubs, and my recollection is that they were the only interested party in studying ground-based augmentation instead of WAAS and/or being content with ILS. It was the early days of GPS when my minimums on a GPS approach were identical to (or higher than) the minimums on an NDB approach... If you look at the FAA's own website, it's basically dead with no new information for several years: https://laas.tc.faa.gov/

Given the success and lower cost of GPS/RNAV approaches for equipment maintenance and approach design, and the relative performance, I would be surprised if GLS/GBAS/LAAS is built out any further. New development for NextGen in the RNAV world is building out DME-only facilities for DME/DME-RNAV, which is mainly the domain of Transport Category aircraft.

My only caveat is that a newer generation of WAAS receivers may come out which will enable GPS/RNAV-based Precision Approaches. That requires alerting to a degredation of signal integrity within 6.0 seconds, and GPS currently alerts at 6.2 seconds. (Yes, a whopping 0.2 seconds between ICAO Annex 10, Volume 1, Chapter 3, Section 7 requirements for a Precision Approach and the system design for LPV and LPV200 approaches, to consider them "Precision.")

Just posted and didn't see this. Yes. Exactly. I found the same web site. Looks like this project isn't going anywhere. Thanks.

 

[Lunar Module]

It’s not the tech, we have full WAAS

Presumably because LPV approaches don't meet the ICAO definition of a precision approach? In the real world, is there any significant advantage of ILS over LPV? Or vice versa? Thx.

 

[cailloux]

Now I can focus my attention on whether it's time to dump ILS/VOR and go strictly GPS based or not when planning a future avionics upgrade.

For the minor incremental cost in avionics, I'd strongly encourage installing ILS/VOR. If retrofitting an aircraft, you probably have the antennas, and ILS/VOR gives you the backup of ground-based facilities for navigating and approaches. We all take different approaches to flying, but I'll regularly have VORs tuned in as a backup and cross-check of my position. I'm a child of the Magena Line, but I'm three button presses away from navigation by VOR in the event of an issue.

Additionally, if you're at an airport with an advantagous VOR approach, and not an "equivalent" RNAV, you can still fly the approach with RNAV presentation as long as you monitor the VOR signal. Catalina (AVX) is the one that I use as an example of this with students. There aren't many like this left, but it's still a non-zero number.

Fun bonus fact since you read this long: the RNAV (GPS) X RWY 24 at CRQ has RF legs (radius-to-fix, or turning legs) on the approach, and is the only such approach I'm aware of that isn't Authorization Required.

 

[cailloux]

In the real world, is there any significant advantage of ILS over LPV?

Ground interference caused by aircraft or metal structures near the runway can interfere with the ILS signals. I'll see notes in either the approach or a NOTAM that prohibit the use of autopilot to the DA on an ILS. Additionally, ILS needles will wiggle on me in a way that I need to be cognizant of and make sure I'm cross-checking if the needles start jumping around caused by other aircraft/equipment.

If a GPS approach degrades from LPV to LNAV/VNAV, I'll need to see that change on the display and use those higher minima on the approach. If I didn't brief the LNAV/VNAV minima, then I'm going missed if I get a signal degredation that takes me off the LPV.

Practically, I'm mostly on LPV approaches, but I'll still do the odd ILS. It's mainly a distinction without a difference, but there are nuances between the approaches. I tend to brief/fly whatever is advertised on ATIS, unless there's a compelling reason for something else.

 

[Lunar Module]

Ground interference caused by aircraft or metal structures near the runway can interfere with the ILS signals. I'll see notes in either the approach or a NOTAM that prohibit the use of autopilot to the DA on an ILS. Additionally, ILS needles will wiggle on me in a way that I need to be cognizant of and make sure I'm cross-checking if the needles start jumping around caused by other aircraft/equipment.

If a GPS approach degrades from LPV to LNAV/VNAV, I'll need to see that change on the display and use those higher minima on the approach. If I didn't brief the LNAV/VNAV minima, then I'm going missed if I get a signal degredation that takes me off the LPV.

Practically, I'm mostly on LPV approaches, but I'll still do the odd ILS. It's mainly a distinction without a difference, but there are nuances between the approaches. I tend to brief/fly whatever is advertised on ATIS, unless there's a compelling reason for something else.

Thanks. Great info. Much appreciated.

 

[tsts4]

My $.02 is I like having options. So I have both a nav radio (2 actually) for LOC/VOR/GS and an IFR GPS navigator. The GPS is the most practical for navigation in the NAS and it opens thousands of airports to approaches with precision like minima equal to that of an ILS (eg LPV) without the investment in ground equipment plus the associated maintenance. A nav radio is SIGNIFICANTLY less expensive to install plus there's no databases to maintain but the utility for GA is reduced, which will only become more acute in the future as ILS's and VOR's are decommissioned down to level necessary to maintain the MON. That said, I'm an advocate for installing both because when you're in IMC and have a failure of one it's very comforting to have a backup that's based upon different technology.

 

[Larry in TN]

GBAS just means "ground based augmentation system"

That used to be called LAAS (Local Area...) vs WAAS (Wide Area...). That terminology was replaced with GBAS some time ago.

As I understand it, the NextGen GBAS systems are LOCAL to each airport

Yes, and a single GBAS installation serves the entire airport and can support multiple approaches to every runway. That allows more approaches to more runways without having to install separate ILS systems for each. It is also somewhat portable so the GBAS equipment can be evacuated prior to a hurricane, for example, and quickly reinstalled after the storm restoring all of the airport's GLS approaches.

Apparently with the right equipment and training you can shoot a Cat III landing with this system.

I have not heard of any that are below CAT I minimums at this time but autoland capability is (was?) planned.

We have GLS capability in many of our 737s. I've flown them at both EWR and IAH.

The only airliners, that I've seen, with LPV capability have been E175s. There are likely more but it's a relatively recent development.

 

[RussR]

Those are United (ex-Continental) hubs, and my recollection is that they were the only interested party in studying ground-based augmentation instead of WAAS and/or being content with ILS. It was the early days of GPS when my minimums on a GPS approach were identical to (or higher than) the minimums on an NDB approach... If you look at the FAA's own website, it's basically dead with no new information for several years: https://laas.tc.faa.gov/

Given the success and lower cost of GPS/RNAV approaches for equipment maintenance and approach design, and the relative performance, I would be surprised if GLS/GBAS/LAAS is built out any further. New development for NextGen in the RNAV world is building out DME-only facilities for DME/DME-RNAV, which is mainly the domain of Transport Category aircraft.

I'm not refuting anything you say, but I will point out that the SFO GLS approaches were just published about 4 years ago.

 

[Larry in TN]

I'm not refuting anything you say, but I will point out that the SFO GLS approaches were just published about 4 years ago.

Yeah, very little going on on the GLS front. The addition of the SFO GLS approaches is the only thing I've seen happen in the last ten years. (Maybe IAH was within that ten years?) Doesn't seem like they're moving forward with them with any enthusiasm.

 

[flyingcheesehead]

Definitely don't wait. LAAS/GBAS has been effectively dead for years at the FAA. In addition, I doubt that you'd see any advantage as a GA pilot. We already get 200-foot minimums on many/most LPV approaches, equivalent to an ILS Cat I. If you look at the requirements for doing Cat II and Cat III ILS approaches, you might expect to see the same thing with a LAAS/GBAS augmented approach that goes below 200 feet, and it's just not feasible for GA.

So, get yourself a nice WAAS GPS and fly the pants off it. LAAS/GBAS/GLS is unlikely to find any use in GA in our flying lifetimes IMO - They were talking about it when I got my Private 20+ years ago.

 

[MauleSkinner]

For what it’s worth, LAAS/GBAS works very well in a tractor.

 

[Larry in TN]

LAAS/GBAS has been effectively dead for years at the FAA.

Yeah, I wouldn't be surprised to see it fade away like the MLS did. RNP approaches and procedures seem to be taking over.

 

[John Collins]

GPS WAAS uses a single GPS antenna where the corrections and integrity data are delivered via WAAS satellites (SBAS is the generic term). The system consists of 38 ground monitoring stations throughout the US, Canada, and Mexico. They measure actual verses GPS determined locations and provide correction to uplink stations that send to the SBAS geostationary satellites, that in turn send to the WAAS GPS. The GBAS system uses ground stations near the airport and use VHF radio to uplink corrections to the aircraft. So a GLS needs both a top mounted GPS antenna and a bottom mounted VHF antenna and a VHF receiver. I don't see GLS ever making it into GA. The next generation of GA GPS systems will be dual frequency, multi constellation systems that will provide the capability for LPV like approaches, world wide, even when outside of an SBAS service volume such as WAAS. As far as when LPV will be considered as precision approaches, that is already the case in ICAO and in the works at the FAA.

 

[Lunar Module]

Great and very interesting info from all. Thank you very much.

 

[Lunar Module]

For what it’s worth, LAAS/GBAS works very well in a tractor.

I've seen some YouTube videos of huge Deere harvesters working a field with automated path control. Is that how they do it? Seems logical. However it works, it's incredible technology. Between the big machines and the computerized controls and the GPS and all else that makes them work they must cost a fortune.

 

[MauleSkinner]

I've seen some YouTube videos of huge Deere harvesters working a field with automated path control. Is that how they do it? Seems logical. However it works, it's incredible technology. Between the big machines and the computerized controls and the GPS and all else that makes them work they must cost a fortune.

Yup…they put a transmitter somewhere that gets maximum coverage, and the accuracy is amazing.

And yup, spendy.

 

[midwestpa24]

Just my $.02, no matter what they call it, GLS, GBAS, etc., typical GA aircraft will not see any reduction in approach mins below what we have for ILS or LPV (200/.5). Cat II and Cat III approaches are more than just navigation equipment, it is an entire other level of certification and training that only the turbine crowd will probably ever have access too, or the need.

 

[Martin Pauly]

So I am wondering if any of you have an opinion on how soon we might see GLS equipment at airports and GLS capable GPS navigators available for the GA market?

Probably never. The only additional capability it would unlock (over SBAS/LPV) is CAT II and III approaches, which is an extremely rare thing in the light GA world (CAT II) or non-existent (CAT III).

I was working on GBAS/GLS airborne equipment back in the 1997. It hasn’t exactly taken off since then, even though many airliners have the capability.

- Martin

 

[Lunar Module]

Probably never. The only additional capability it would unlock (over SBAS/LPV) is CAT II and III approaches, which is an extremely rare thing in the light GA world (CAT II) or non-existent (CAT III).

I was working on GBAS/GLS airborne equipment back in the 1997. It hasn’t exactly taken off since then, even though many airliners have the capability.

- Martin

Thanks. Seems to be the consensus around here.

Oh, and I have enjoyed your YouTube videos. Thanks for posting them!

 

[Trogdor]

For everyone here are two really great links with video:

* https://www.faa.gov/about/office_or...nits/techops/navservices/gnss/laas/howitworks
* https://www.faa.gov/about/office_or...nits/techops/navservices/gnss/waas/howitworks

The main thing about WAAS is that the corrections made on the ground (master sites) are rebroadcasted to geosynchronous satellites which in turn send these corrections to aircraft as a GPS packet which in turn is used with the original GPS signal to determine position (these corrections btw are probably time deltas not position offsets, GPS is all about TIME despite its acronym).

As @John Collins mentioned, you need multiple antennas for GLS to receive the corrections from the ground (VHF) and in the air (GPS Satellite). While with SBAS systems like WAAS only one antenna is required since both the correction packet and the original GPS signal are on the same frequency.