MLS Approaches

Mon Jun 12, 2000 11:38 pm

Can someone please explain how MLS approaches work? Thanks.
Posts: 63
Joined: Tue Jun 13, 2000 12:28 am

RE: MLS Approaches

Tue Jun 13, 2000 12:32 am

The MLS, or Microwave Landing System, was designed to eventually replace the ILS (Instrument Landing System) at large airports across the world. What it does is provide precision guidance (both lateral and verticle) to aircraft approaching a runway. It is VERY similar to the ILS which has widespread use across the world. Infact, one would not be incorrect to think of MLS as an upgraded, or expanded ILS. The key "selling points" for the MLS is the fact that it is much more accurate and precise than the original ILS. It has an operational frequency range from 5031 to 5091 MHz; 200 channels - more than enough for worldwide implementation. Its range is signifigantly greater than ILS, capable of lateral reception of +/- 60 degrees within 14 miles, and +/- 40 degrees outward towards 20 miles. Vertically, it is capable of reception at a 30 degree angle, all the way up to 20,000 feet, while still maintain a 3 degree glide path. All MLS would contain DME (Distance Measuring Equipment) to provide pilots with exact information as to how far out from the runway they really are. The Final high point of the MLS is what is called "Data Content" and "Auxiliary Data Content". When tuned to an operating MLS, pilots would be provided with the following information: Station ID, Ground Equipment and performance level, DME channel and status, 3-D location of MLS equipment, waypoint coordinates, runway conditions, and weather (RVR/Runway Visual Range, Cloud Ceiling, Altimeter setting, Wind, wake turbulence, wind shear). The MLS also has more sophisticated capabilities, such as curved and segmented approaches, selectable glidepath angles, and accurate 3-D positioning of aircraft in space. These will be implemented as aircraft begin to be better equipped with more advanced MLS instrumentation.
Posts: 1923
Joined: Fri Apr 28, 2000 12:42 am

RE: MLS Approaches

Tue Jun 13, 2000 10:43 pm

That is fine in theory. But in practice, it's another story. In a nutshell, MLS has been dumped. I do not recall the exact technical reason as to why, but MLS will not be implemented. On the ICAO website, I found this : "The current strategy for the application of non-visual aids to approach and landing was recommended at the Special Communications/Operations Divisional Meeting held at ICAO Headquarters in spring, 1995. Delegates to that meeting discussed future ICAO policy in all-weather operations and concluded that, for a variety of reasons, it had become impracticable to proceed with implementation of the global ILS/MLS transition plan. " The article goes on to say that the future of "non-visual aids to approach and landing" lies with satelites systems, such as GPS and a few others.
Never let the facts get in the way of a good theory.
Posts: 63
Joined: Tue Jun 13, 2000 12:28 am

RE: MLS Approaches

Wed Jun 14, 2000 12:50 am

I agree and disagree. You are correct in saying that MLS was never, or atleast has not yet been, implemented as planned, mainly due to the new promises of satelite/GPS approaches. However, the ICAO/FAA has since drastically reduced funding for the development of WAAS/enhanced GPS/RNAV approaches. This leads me to believe that they might again consider the ILS, or its expanded version, the MLS for worldwide implementation. The ICAO was only garaunteeing that the ILS system would be in use through 1995, and then they were planning to go with coupled MLS/ILS systems, and then eventually go all MLS when the users (Pilots) upgraded their equipment. However, when GPS became available for aviation, the ICAO and FAA (probably the CAA too) saw these as a more capable and worthwhile replacement. So they had these two roads to go down, and they chose to go with GPS. Unfortunately, current development of GPS data to be used as a replacement to the ILS is "dead in the water". Perhaps they will chose to resume development of the other road, with MLS.
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Joined: Fri Mar 16, 2007 1:29 pm

RE: MLS Approaches

Thu Jun 15, 2000 12:22 pm

There was a great lobby within Canadian civil aviation in the eighties to enhance the LORAN chain system as the equipment to access the signal was the cheapest available, especially to the private owners. The government resisted due to its research and pending approval of MLS. In fact, the Cdn government decided that the next century's replacement for the ILS would be the MLS. They funded a research project that lasted over ten years, and helped in the development of a small company in Cape Breton that would ultimately benefit/profit from MLS onboard and ground-based equipment (primarily ground based).

And then along came GPS. Within 6 months of the Tidal Wave that was GPS came the demise of not only the "long term" philosophy of the government, but of the R&D facilities in Nova Scotia.

MLS died a sudden and quick death in Canada about 7 years ago!

(Apologies for any timeline errors - I'm going from my faulty memory of events)

Best Regards,


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