What Happened to the Microwave Landing System?
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While CAT I is approved, other CAT's are in the approval phase with the FAA and others.
Also, in the US, currently GBAS is not funded by the FAA so the airlines have to pay for everything (ground equipment, site installation, flight testing, aircraft avionics upgrades, operations, etc.) I think after doing cost/benefit analysis, they are happy to just stick with CAT I GLS for now and are not in a hurry implement GAST-D.
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You dont look at a GBAS standard, you look at the accuracy required for CAT III autoland, and meet or exceed that.
That accuracy level is already in place in the standards, it is only a matter of validating the system to meet the standard.
There are many places in the world, and in the military, where the validation does not need to be decades long as with the FAA, but months.
There are GBAS CAT III autoland aircraft and procedures already in operation, much of it government, but there are others...
a GBAS system is part of the airport infrastructure, same as an ILS, and other NAVAIDS. The airlines do not pay for the system at the airport, the airlines pay for the system on the aircraft.
To outfit an airport with a GBAS system costs about $2 Million, and is good for 26 runway ends and that cost includes maintenance of the system. This cost also includes the approach procedures.
An ILS system costs $500,000 per runway end, and requires about $100,000 a year in maintenance, per runway end. The ILS has all of the multi-path and interference issues, and GBAS has none of these.
The simple costs of it all show that the GBAS is far less expensive, and far more powerful for operations.
If you were an airline paying for the navaid, and the capability... what would you want to pay for?
EDIT: Per the FAA
"The Federal Aviation Administration (FAA) work program is now focused on validating standards for a GBAS Approach Service Type-D (GAST-D) (CAT-III minima) service. The program currently projects a GAST-D GBAS system can be available in 2018."
"ICAO should approve Standards and Recommended Practices for GBAS Category II/III (GAST-D) systems in 2015."
Under SESAR JU, we had GBAS CAT II/III standards approved and validated back in December 2015...
There are a few States which have already approved GBAS for CAT III, and procedures have been designed and are in use.
That accuracy level is already in place in the standards, it is only a matter of validating the system to meet the standard.
There are many places in the world, and in the military, where the validation does not need to be decades long as with the FAA, but months.
There are GBAS CAT III autoland aircraft and procedures already in operation, much of it government, but there are others...
Also, in the US, currently GBAS is not funded by the FAA so the airlines have to pay for everything (ground equipment, site installation, flight testing, aircraft avionics upgrades, operations, etc.)
To outfit an airport with a GBAS system costs about $2 Million, and is good for 26 runway ends and that cost includes maintenance of the system. This cost also includes the approach procedures.
An ILS system costs $500,000 per runway end, and requires about $100,000 a year in maintenance, per runway end. The ILS has all of the multi-path and interference issues, and GBAS has none of these.
The simple costs of it all show that the GBAS is far less expensive, and far more powerful for operations.
If you were an airline paying for the navaid, and the capability... what would you want to pay for?
EDIT: Per the FAA
"The Federal Aviation Administration (FAA) work program is now focused on validating standards for a GBAS Approach Service Type-D (GAST-D) (CAT-III minima) service. The program currently projects a GAST-D GBAS system can be available in 2018."
"ICAO should approve Standards and Recommended Practices for GBAS Category II/III (GAST-D) systems in 2015."
Under SESAR JU, we had GBAS CAT II/III standards approved and validated back in December 2015...
There are a few States which have already approved GBAS for CAT III, and procedures have been designed and are in use.
Last edited by underfire; 25th Jan 2017 at 06:52.
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@underfire
What you quote there is from an old document. Here's what the current version states:
https://www.faa.gov/about/office_org...a/GBAS_FAQ.pdf
So again, the standards have not yet been published, and even design approval isn't expected until 2019. That means an operational GAST-D system will not be available until 2020 or beyond.
Furthermore, as mentioned earlier, GBAS in the US is considered a NON-FEDERAL system. It is NOT like ILS or other NAVAIDs which are paid for and maintained by the FAA.
So although GBAS is part of the airport infrastructure, the funding for GBAS has to come from primarily from the users, i.e., airlines. The airport authority might contribute some seed amount, but at the end of the day, it is the airlines which benefit from the system so if they want GBAS they're expected to burden the bulk of the cost (through fees, etc.)
Extracts from FAA material:
Considering that currently:
What you quote there is from an old document. Here's what the current version states:
The FAA expects ICAO GAST-D Standards and Recommended Practices (SARPS) will be approved in 2016 for publication in 2018.
The FAA is currently supporting a non-Federal applicant’s request for System Design Approval (SDA) for a GAST-D GBAS. The FAA currently projects that this SDA will be finalized in 2019.
The FAA is currently supporting a non-Federal applicant’s request for System Design Approval (SDA) for a GAST-D GBAS. The FAA currently projects that this SDA will be finalized in 2019.
So again, the standards have not yet been published, and even design approval isn't expected until 2019. That means an operational GAST-D system will not be available until 2020 or beyond.
Furthermore, as mentioned earlier, GBAS in the US is considered a NON-FEDERAL system. It is NOT like ILS or other NAVAIDs which are paid for and maintained by the FAA.
So although GBAS is part of the airport infrastructure, the funding for GBAS has to come from primarily from the users, i.e., airlines. The airport authority might contribute some seed amount, but at the end of the day, it is the airlines which benefit from the system so if they want GBAS they're expected to burden the bulk of the cost (through fees, etc.)
Extracts from FAA material:
A Category 1 (CAT 1) GBAS system is available and in use in the National Airspace System. While the FAA has indefinitely delayed plans for federal GBAS acquisition, the system can be purchased by airports and installed as a Non-Federal navigation aid. ...
What is a Federal System versus a non-Federal system?
Throughout the National Airspace System, you will find a mixture of Federal and non-Fed navigational aids. The Federal systems are paid for and maintained by the FAA. However, some airports, cities, and/or private entities may purchase and maintain a navigational aid for either private or public use. These navigational aids are known as non-Fed systems because the FAA did not purchase them, nor does the FAA maintain them. However, to ensure public safety, the FAA does retain the power to approve or not approve these non-Fed systems; additionally, they inspect them annually.
What is a Federal System versus a non-Federal system?
Throughout the National Airspace System, you will find a mixture of Federal and non-Fed navigational aids. The Federal systems are paid for and maintained by the FAA. However, some airports, cities, and/or private entities may purchase and maintain a navigational aid for either private or public use. These navigational aids are known as non-Fed systems because the FAA did not purchase them, nor does the FAA maintain them. However, to ensure public safety, the FAA does retain the power to approve or not approve these non-Fed systems; additionally, they inspect them annually.
If you were an airline paying for the navaid, and the capability... what would you want to pay for?
- ILS -- paid for by the FAA
- GBAS -- paid for by the airlines
Last edited by peekay4; 25th Jan 2017 at 09:04.
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In BA, only the A320 series aircraft are equipped for MLS. LHR provides MLS approaches to all four runways. BA expect all suitably equipped aircraft to fly MLS approaches where they are available. On the current network this is only LHR.
The reason for this is, MLS allows closer approach spacing (and therefore, flow rate) than ILS in LVPs. All down to the same Cat 3b minima of 75m, no DH.
ATC weren't able to utilise this improved flow rate, as they said they didn't know which aircraft were eligible for reduced spacing. So in order to 'help', BA expect their SIAs to always 'fly the wave'! This was an attempt to satisfy ATC's concern and enable the higher flow rate in LVPs. Sadly this has not happened. Possibly because a few A320 have never been suitably equipped.
So in short, apart from being an additional 'back up', and the fact that microwave is a more solid and reliable signal than ILS, there is absolutely no benefit whatsoever. Just a huge amount of significant expense. I make no comment as to whether this expense, is the only REAL reason BA A320s fly the microwave at LHR.
The reason for this is, MLS allows closer approach spacing (and therefore, flow rate) than ILS in LVPs. All down to the same Cat 3b minima of 75m, no DH.
ATC weren't able to utilise this improved flow rate, as they said they didn't know which aircraft were eligible for reduced spacing. So in order to 'help', BA expect their SIAs to always 'fly the wave'! This was an attempt to satisfy ATC's concern and enable the higher flow rate in LVPs. Sadly this has not happened. Possibly because a few A320 have never been suitably equipped.
So in short, apart from being an additional 'back up', and the fact that microwave is a more solid and reliable signal than ILS, there is absolutely no benefit whatsoever. Just a huge amount of significant expense. I make no comment as to whether this expense, is the only REAL reason BA A320s fly the microwave at LHR.
4468, I suspect that BA were given an incentive to fit MLS receivers on a few 757s(?) as part of the MLS trials - UK flag wave. Other operators did not believe that the ground installation would be continued, particularly as the UK submission was rejected. I don't know why the ground system was retained.
Manchester and Gatwick had trial installations for interference tests and Cat 3 evaluation (plus a low approach over Gatwick electric railway). Manchester considered a weaving 'S' approach to 24 avoiding several hospitals, but this was not flight tested.
MLS would have been able to provide a GBAS type of operation with appropriate on board computing, e.g. parallel runway operation to a lower standard; also a computed GS together using the back course (go around guidance) beam to the opposite runway end.
Another consideration at LHR was to use a computed steep approach GS on the front course to a displaced touchdown for 'STOL' regional aircraft to reduce the wake turbulence spacing. (Reconsidered more recently with ILS?)
Overseas MLS trials used installations at Bern and Tehran. Steep approach and segmented approaches were demonstrated at Bern with 4 deg autoland; also take off and GA guidance was tested towards 'the close in hill'. Bern also provided an offset MLS for a cross field grass runway towards the ground station, as well as maintaining the full 'ILS' on the paved surface.
There were associated trials with helicopters, but I don't recall where. Some of the ideas would have enabled multiple approach paths and GS to platforms and one idea was for simultaneous helicopter IFR approaches to LHR from the South with a landing zone where T4 is.
Manchester and Gatwick had trial installations for interference tests and Cat 3 evaluation (plus a low approach over Gatwick electric railway). Manchester considered a weaving 'S' approach to 24 avoiding several hospitals, but this was not flight tested.
MLS would have been able to provide a GBAS type of operation with appropriate on board computing, e.g. parallel runway operation to a lower standard; also a computed GS together using the back course (go around guidance) beam to the opposite runway end.
Another consideration at LHR was to use a computed steep approach GS on the front course to a displaced touchdown for 'STOL' regional aircraft to reduce the wake turbulence spacing. (Reconsidered more recently with ILS?)
Overseas MLS trials used installations at Bern and Tehran. Steep approach and segmented approaches were demonstrated at Bern with 4 deg autoland; also take off and GA guidance was tested towards 'the close in hill'. Bern also provided an offset MLS for a cross field grass runway towards the ground station, as well as maintaining the full 'ILS' on the paved surface.
There were associated trials with helicopters, but I don't recall where. Some of the ideas would have enabled multiple approach paths and GS to platforms and one idea was for simultaneous helicopter IFR approaches to LHR from the South with a landing zone where T4 is.
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The BA trials at LHR were in the nineties, with one 757 (G-BIKO?) and one 767 (G-BNWB) with a chequerboard painted on the nose cone. The MLS was on 27R and could only be flown manually to CAT 1 minima, the main reason people requested it was when 27L was the landing runway and you wanted to use 27R to park on the old T1 shuttle stands...
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4468,
Sorry, this is not quite true. Approach do not have access to the flight plan item where MLS equipment is entered, hence why the crews request MLS approach on first contact. Tower's electronic strip system extracts the item and displays MLS capability on the strip.
As you say, LHR LVP traditionally occurs between 0600-1100ish, so it makes sense that the first inbound wave would give the greatest benefit. However, the higher flow rate has certainly been achieved. BA A320 series aircraft would land using MLS on the departure runway, so the flow rate went from 24-26 in LVP to 28-30 due to MLS. On the arrival runway we would use 5nm gaps ahead of the MLS a/c, compared to 6nm ahead of ILS a/c.
Now we have enhanced ILS systems, which have the same, smaller, sensitive area as the MLS, it's benefits have been equalled: We run with 5nm behind any Medium wake cat aircraft.
ATC weren't able to utilise this improved flow rate, as they said they didn't know which aircraft were eligible for reduced spacing. So in order to 'help', BA expect their SIAs to always 'fly the wave'! This was an attempt to satisfy ATC's concern and enable the higher flow rate in LVPs. Sadly this has not happened. Possibly because a few A320 have never been suitably equipped.
As you say, LHR LVP traditionally occurs between 0600-1100ish, so it makes sense that the first inbound wave would give the greatest benefit. However, the higher flow rate has certainly been achieved. BA A320 series aircraft would land using MLS on the departure runway, so the flow rate went from 24-26 in LVP to 28-30 due to MLS. On the arrival runway we would use 5nm gaps ahead of the MLS a/c, compared to 6nm ahead of ILS a/c.
Now we have enhanced ILS systems, which have the same, smaller, sensitive area as the MLS, it's benefits have been equalled: We run with 5nm behind any Medium wake cat aircraft.
Going back to the original thread starter question, there is a reasonably accurate history of MLS development here:
https://en.wikipedia.org/wiki/Microwave_landing_system
At a meeting of the Royal Institute of Navigation at Canary Wharf London in 1994, the USA presented a number of papers defining the GPS system.
Many Europeans present were outraged that the USA had developed this system without their participation or consultation. Seriously, it's true - I was there. The USA members were somewhat taken aback, this was their system designed for their military but with free access available to the Standard Positioning System to any and all users.
Then and there, the European members resolved they were going to have their own Sat Nav system because they did not trust the USA and its total control of GPS. That was the intellectual birth of Galileo back in 1994. How is that going, fully operational yet?
At that time MLS was officially approved by ICAO and was to become mandatory fitment in the future, BUT
ICAO held a special COM-OPS division meeting in Montreal in 1995.
The Australian company I worked for held a reception for all delegates promoting our AWA-Intescan MLS ground equipment.
The next day and at that meeting, the USA delegate read out a letter from President Clinton offering ICAO free use of GPS into the future and guaranteeing at least seven years notice of withdrawal. He also indicated that the "dithering" or positional degradation then operating on the Standard Positional Service (Accuracy CEP of 100 feet) would be turned off thus improving accuracy of SPS by an order of magnitude.
That meeting was the end of the road for MLS as an ICAO mandatory fitment item. And FREE beats COSTLY every time. Precious few operators or authorities were prepared to continue with an MLS program in these circumstances.
Certainly some countries in Europe continued with MLS installation for various local reasons including frequency congestion, interference with ILS, and plain distrust of GPS. A couple of military MLS systems also were installed in Asian countries but general development of the system virtually ceased.
GPS WAAS and its variants plus GBAS systems (Ground Local Area Augmentation Systems) are becoming the future and there are GBAS systems in Air Transport use in various parts of the world.
Hope that answers the original question!
https://en.wikipedia.org/wiki/Microwave_landing_system
At a meeting of the Royal Institute of Navigation at Canary Wharf London in 1994, the USA presented a number of papers defining the GPS system.
Many Europeans present were outraged that the USA had developed this system without their participation or consultation. Seriously, it's true - I was there. The USA members were somewhat taken aback, this was their system designed for their military but with free access available to the Standard Positioning System to any and all users.
Then and there, the European members resolved they were going to have their own Sat Nav system because they did not trust the USA and its total control of GPS. That was the intellectual birth of Galileo back in 1994. How is that going, fully operational yet?
At that time MLS was officially approved by ICAO and was to become mandatory fitment in the future, BUT
ICAO held a special COM-OPS division meeting in Montreal in 1995.
The Australian company I worked for held a reception for all delegates promoting our AWA-Intescan MLS ground equipment.
The next day and at that meeting, the USA delegate read out a letter from President Clinton offering ICAO free use of GPS into the future and guaranteeing at least seven years notice of withdrawal. He also indicated that the "dithering" or positional degradation then operating on the Standard Positional Service (Accuracy CEP of 100 feet) would be turned off thus improving accuracy of SPS by an order of magnitude.
That meeting was the end of the road for MLS as an ICAO mandatory fitment item. And FREE beats COSTLY every time. Precious few operators or authorities were prepared to continue with an MLS program in these circumstances.
Certainly some countries in Europe continued with MLS installation for various local reasons including frequency congestion, interference with ILS, and plain distrust of GPS. A couple of military MLS systems also were installed in Asian countries but general development of the system virtually ceased.
GPS WAAS and its variants plus GBAS systems (Ground Local Area Augmentation Systems) are becoming the future and there are GBAS systems in Air Transport use in various parts of the world.
Hope that answers the original question!
