What Happened to the Microwave Landing System?
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What Happened to the Microwave Landing System?
I remember reading about the Microwave Landing System (MLS) years ago in aviation textbooks in the states. Supposedly, (back then), the MLS was going to be all the rage and replace most ILSs. What happened? I don't know of any MLS approaches? Was it a funding issue as to why the MLS never went forward or did the GPS do in the MLS?
Thanks.
Thanks.
It was a victim of GPS technology, lots of dollars spent developing it in many countries, have a quick google of MLS, INTERSCAN, Wiki links contain some concise info.
I remember reading about the Microwave Landing System (MLS) years ago in aviation textbooks in the states. Supposedly, (back then), the MLS was going to be all the rage and replace most ILSs. What happened? I don't know of any MLS approaches? Was it a funding issue as to why the MLS never went forward or did the GPS do in the MLS?
MLS is not supplanting ILS, in fact MLS will be dead and buried within a few years. It's not that funding is going to run out, it's that nobody manufactures the system any more, and the current one is about to reach it's end of life. The main benefits of MLS (smaller sensitive area in CAT II/III ops) have largely been replicated by the new 32-element array ILS localiser antenna on the market now anyway.
A standard RNAV GNSS (APV Baro VNAV) approach can't get to the same decision height as a CAT I ILS, so that won't do it either.
GBAS will, especially when CAT III certification is granted.
However, even new aircraft coming out of the factories now are noit fitted for GBAS, so ILS will be around for another 30 years at least.
A standard RNAV GNSS (APV Baro VNAV) approach can't get to the same decision height as a CAT I ILS, so that won't do it either.
GBAS will, especially when CAT III certification is granted.
However, even new aircraft coming out of the factories now are noit fitted for GBAS, so ILS will be around for another 30 years at least.
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While I have flown with aircraft having MLS buttons on the guidance panel, I have never seen an MLS receiver or an airport equipped with MLS.
Much like airline STOL, MLS was required for too small a niche and provided too little benefits to be successful. With airlines having very long life cycles it may take decades to equip a fleet with new technology if that technology is not mandatory equipment.
Much like airline STOL, MLS was required for too small a niche and provided too little benefits to be successful. With airlines having very long life cycles it may take decades to equip a fleet with new technology if that technology is not mandatory equipment.
There is a further level in RNAV approaches called LPV which provides a D/H below LNAV/VNAV minimums, typically around 200' which is ILS CAT 1.
MLS simply got overtaken before it got started.
MLS simply got overtaken before it got started.
I've often wondered about MLS. Ever since we picked up our company S-76B from maintenance and found shortly afterwards that some "helpful" avionics engineer had been fiddling and had changed the ILS receiver frequencies to MLS. We found out in solid IMC whilst being vectored for the ILS. We had no idea this was possible and had no idea how it had been done, or how to change it back again. That caused a few more grey hairs.
FWIW most of BA's Shortfall Airbus fleet is MLS equipped (but not the 744/777s, not sure about their 787s).
As a result of the above LHR offers published MLS approaches down to CAT 3b no DH limits (typically 75 metres RVR) for all runways ....so I'm not sure where this idea that MLS is already a victim of GPS or that it has been overtaken already by RNAV approaches has come from. As I understand it MLS is still technically more capable than RNAV/GPS when it comes to genuine low vis ops, but I'd agree that unlike GPS/RNAV it's a technology that's not going anywhere.
As for the "why?" and the original question:as I recall it during the introduction MLS it was being pushed as having lots of advantages verses an ILS: for example curved approaches to low minima - which in reality was not going to happen at many airports e.g. due noise routings; OTOH it provides reduced spacing down the approach- which I believe (an ATCer no doubt will confirm or deny) is a facility LHR ATC use to their advantage to improve the flow rate during Low Vis ops - but whilst it's all good stuff as I understand it unlike GPS/RNAV MLS basically doesn't provide enough commercial advantages 24/7 to have make it a "killer app" vs ILS.
As a result of the above LHR offers published MLS approaches down to CAT 3b no DH limits (typically 75 metres RVR) for all runways ....so I'm not sure where this idea that MLS is already a victim of GPS or that it has been overtaken already by RNAV approaches has come from. As I understand it MLS is still technically more capable than RNAV/GPS when it comes to genuine low vis ops, but I'd agree that unlike GPS/RNAV it's a technology that's not going anywhere.
As for the "why?" and the original question:as I recall it during the introduction MLS it was being pushed as having lots of advantages verses an ILS: for example curved approaches to low minima - which in reality was not going to happen at many airports e.g. due noise routings; OTOH it provides reduced spacing down the approach- which I believe (an ATCer no doubt will confirm or deny) is a facility LHR ATC use to their advantage to improve the flow rate during Low Vis ops - but whilst it's all good stuff as I understand it unlike GPS/RNAV MLS basically doesn't provide enough commercial advantages 24/7 to have make it a "killer app" vs ILS.
Last edited by wiggy; 21st Jan 2017 at 09:14.
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Originally Posted by wiggy
for example curved approaches to low minima
A nice writeup is here.
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Can MLS really do curved?
In principle this is not very different from a GPS approach.
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Now there is GBAS...even with CAT III autoland. Curved approach, multiple threshold, and able to use the same runway end for both ARR and DEP (not that one would really want to)
System is not complicated, and new ac's already come standard.
System is not complicated, and new ac's already come standard.
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I have never seen an MLS receiver or an airport equipped with MLS.
Do the MMRs have optional modules for MLS?
Lax had a MLS in the past. Even though the technology was developed more than 40 years ago I believe the US Military are still a major user with a MLS receiver standard equipment on the C17 and most C130's. I remember seeing the initial test installation at Melbourne in Australia.
Now there is GBAS...even with CAT III autoland........
System is not complicated, and new ac's already come standard.
System is not complicated, and new ac's already come standard.
The (albeit dated article) implies autoland off a 50DH, which whilst impressive if true is still not as capable as the MLS at the likes of LHR.
FAA Targets 2018 For GPS-Based Autoland Capability | Commercial Aviation content from Aviation Week
The ICAO led initiative for MLS was based on the predicted increase in air transport, the demand for instrument approaches, particularly CAT 3, problems of frequency overlap (runway density), and potential for commercial VHF broadcast interference.
Competing UK and US systems were demonstrated cica 1978/79 with CAT 3 / RNAV performance and integrity which are only just being matched by today's GPS.
The problems were competing political interests in the avionics market, cost, which the operators did not wish to have , and that the perceived threat to ILS was not imminent. The environment / noise lobby was weak, no money, and inability to pressurise the industry.
The GPS card was played as a stalling strategy, but was subsequently mis-interpreted as offering 'the world and more', which influenced the less knowledgable nations during the ICAO evaluation.
The threat faded into history although many of the concepts continued in the military, Madge etc, and specialist private installations e.g. Aspen.
Due to the limited computing power at the time (no FMS), curved approaches used a few 3D waypoints which were linked by existing LOC and GS capture modes in the autopilot. The end result was a very impressive smooth approach which enabled multiple azimuth changes or lateral offsets, and a choice of glide-slope angles and transitions, e.g. 4deg changing to 3deg at 1000ft' and vice versa, as well as straight in steep approach 4 deg.
A 4 deg autoland was demonstrated on a non ILS runway after a 30 deg offset 3 deg GS, transitioning to straight in and 4 deg GS final.
Competing UK and US systems were demonstrated cica 1978/79 with CAT 3 / RNAV performance and integrity which are only just being matched by today's GPS.
The problems were competing political interests in the avionics market, cost, which the operators did not wish to have , and that the perceived threat to ILS was not imminent. The environment / noise lobby was weak, no money, and inability to pressurise the industry.
The GPS card was played as a stalling strategy, but was subsequently mis-interpreted as offering 'the world and more', which influenced the less knowledgable nations during the ICAO evaluation.
The threat faded into history although many of the concepts continued in the military, Madge etc, and specialist private installations e.g. Aspen.
Due to the limited computing power at the time (no FMS), curved approaches used a few 3D waypoints which were linked by existing LOC and GS capture modes in the autopilot. The end result was a very impressive smooth approach which enabled multiple azimuth changes or lateral offsets, and a choice of glide-slope angles and transitions, e.g. 4deg changing to 3deg at 1000ft' and vice versa, as well as straight in steep approach 4 deg.
A 4 deg autoland was demonstrated on a non ILS runway after a 30 deg offset 3 deg GS, transitioning to straight in and 4 deg GS final.
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As far as i know GLS (or GBAS) is only certified for CAT I operation. The company i fly for was the first in europe being certified for operational use of GLS, but only CAT I as well. Autoland and automatic rollout was possible, but not approved. We did however do test flights for CAT IIIb/c trials which were extremely successful, however the system is still not approved for more than CAT I.
Sadly we are not GLS capable anymore as we switched from 737NG where GLS was available at no extra cost from the OEM to airbus where only a retrofit at around 250k € per airframe is available, a cost which is simply to high for no real extra capability.
Sadly we are not GLS capable anymore as we switched from 737NG where GLS was available at no extra cost from the OEM to airbus where only a retrofit at around 250k € per airframe is available, a cost which is simply to high for no real extra capability.
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There are many applications, albeit none commercial for ac, where we are using GBAS for CAT III autoland. While CAT I is approved, other CAT's are in the approval phase with the FAA and others.
Exactly, if one looks at the precision available with GBAS, CAT III autoland is not an issue, you just have to get the regulatory agencies to approve its use.
Just as a turn to final with GBAS is well documented, there are no commercial ac applications. (again, there are a few non-commercial already in use)
We even have RNP AR transition to GBAS final in operation. (military ops)
Autoland and automatic rollout was possible, but not approved.
Just as a turn to final with GBAS is well documented, there are no commercial ac applications. (again, there are a few non-commercial already in use)
We even have RNP AR transition to GBAS final in operation. (military ops)