MLS at EGLL

[Lost_luggage34]

Could anyone be so kind to explain a little of the basics of the MLS at LHR ?

Understand that it is all installed on both runways but not yet in full operation.

Curious to understand a little about how it works vs. traditional ILS which I understand fairly well.


Cheers

[fen boy]

it lets you go round corners

[HEATHROW DIRECTOR]

http://www.nats.co.uk/news/press_releases/2002_03_27.html

Is a link I found using Google. I'm not sure how one goes about sequencing a/c using MLS??

[FWA NATCA]

Lost,

I'm shocked that anyone has an MLS system, here in the US they abandoned the MLS project back in the late 80's, in fact only two airports in the US had an MLS for test purposes (Antrim County Airport in Northern Michigan was one)

Basically the MLS allows you to intercept the localizer at greater angles or to fly a segmented approach, around obsticals (tall buildings, antenna farms, etc). The MLS transmitter was designed as a single unit versus the ILS where you had a seperate glide slope antenna and a seperate localizer antenna.

In theory the MLS was a good design that allowed greater flexibility, but the high cost of installation for the aviation community and GPS/RNAV derailed MLS. Back when I did a feasibility study for the airport that I worked at, the cheapest unit that a GA pilot could purchase for their acft was $6K (six thousand US dollars) well above the cost of an ILS, GPS, or RNAV unit.

Mike

[Gonzo]

Wasn't the main impetus for putting MLS in the increase in capacity in LVPs, due to the much higher resistance to interference, thus no need for the LSA etc?

Increasing traffic in LVPs, lovely, bet we all look forward to that on GMC!

Gonzo.

[Iron City]

Benefits from MLS werealleged to be ability to do multiple runway ends with one equipment installation, less site preparation (rearrangement of the landscape) than ILS. It would allow curved and segmented approaches which could allow some more flexability for constructing instrument approaches.

There is MLS and the is MLS. A system was built for the US military in the 1960s and 70s by I believe, Singer Librascope. that was designed to be easily deployable into new airfields/LZs t o setup and provide instrument type capabilty quickly and easily.

A variation on this system was used by Rocky Mountain Airways with DH-7s in Colorado to provide more reliable flights into ski country airports that ILS could no be installed at or used usefully.

The FAA started into buying about 200 systems from Hazeltine in the early 1980s. This was different than the military systems and met a set of SARPS/MOPS that a number of companies were using including Canadian MArconi and some folks in Europe. After building about 20 system the Hazeltine contract was terminated for a variety of reasons. Systems were installed at Manchester New Hampshire, Haily Idaho and some other locations. There are also some in Alaska, I believe.

After Hazeltine there was still demand by specific operators and airports with specific local conditions for MLS systems so a FAR Part 171 program (where an airport buys the system to FAA specifications, installs it and gets it running and then turns it over to FAA for care and feeding) was started and so far as I know still exists.

The problem with MLS, as alluded to by FWA NATCA was that it didn't provide sufficient operational benefit to users to justify the cost or equiping and operating it. The General Aviation community refused to equip their aircraft because of the expense and lack of more benefits and the GPS was coming along that promied to provide at least a non-precision capability. LORAN C was also popular in GA for a few years in the 1980s as a poor mans RNAV system. In the end MLS is a useful technology in a niche market.

[Ricky Butcher]

MLS may be prohibitively expensive for the GA community, but it could probably make sense for the major commercial operators if just to increase flow rates into busy European airports (LHR specifically) on foggy days. GPS approaches are a great idea in principal, but they ultimately depend on the cooperation of Uncle Sams military. European governments quite rightly eschew the idea of placing their terminal approach guidance in the hands of a slightly paranoid and reactionary foreign superpower.

[Lost_luggage34]

Many thanks for the replies chaps.

[Iron City]

Gee Ricky, U.S. is not a paranoid foreign superpower here, it's a paranoid domestic superpower.

Maybe when Galilleo is put together and the United States of Europe has it's own GNSS you'll feel different. Would you be willingfor france to have the same vote as Ohio in the international fora when this happens?

MLS would improve capacity only if the capabilities for curved and segmented approaches were used and the surveillance and com was sorted out and the aircraft all (or mostly) equipped and the crews trained and current and the controllers trained and current.

[xyz_pilot]

I disagree with you about MLS and capacity.

When the viz or cloud base gets close to Cat 1 airports need to go to LVP’s. This protects the ILS signal and allows safe autolands. One of the protections is to increase the spacing between aircraft on finals and to restrict when departing aircraft can pass the CAT II hold. This substantially reduces the flow rate, particularly at single runway airports.

When the viz get very bad restrictions needed for safe ground movements become the limiting factor. BUT when the viz is 500meters it’s the ILS protection that limits flow rates.

The current straight in approaches used with MLS in met just below Cat I (which is what we have most of the time LVP’s are in effect) would get a lot more Pax to their destination on time. Most airlines in Europe would be willing to pay for this. As for GA, well at the main airports in Europe its not a factor.

As to equipment and training it’s a non-issues for straight in MLS. Most airlines dealt with the issue of FM immune ILS and VOR with “multi-mode” receivers. These just need a MLS card putting in the box. The operation is identical to the crew. So the training should not be much of an issue. You are right about the need for all to have it, but as with RVSM and 8.33 radios there will be a date. Then after the date you will not be able to go to MLS airfields if you don’t have the kit

[niknak]

Interesting responses to the alternatives to the ILS system.

We're outside controlled airspace, fully radar equipped, and are in the process of having to replace our ILS systems.

We looked at MLS, but it was obvious, as has already been stated, that it was going to be prohibitively expensive.
We then investigated the possibility of drawing up GPS approaches, which would have been the cheapest option, as it involves no outlay fro ground equipment by the airport authority.
Again, we've waited for UK CAA approval for this for so long, that the airport authority have decided to invest in new ILS systems.

It appears that the best we can hope for is continuation of the ILS system combined with improvements in GPS technology and approved GPS approaches combined with the ILS.

[Iron City]

Autolands in CAT 1? Why bother having anybody up front driving then? Guess there has to be someone to talk to on the radio.

The MLS signal has very different characteristics than the VHF ILS signals. Don't use marker beacons either as MLS is 3 dimensional. Still need to keep a/c and ground equipment from parking in front of the antennas (there are two, an azimuth station about 5m x 3m and an elevation station that is tall and skinny. The exact placement of hold short lines etc would be a function of the airport and installation, but in most cases are not as limiting as the ILS.

The IFR acceptance capacity for a runway in many cases is driven by the time for the a/c to land, decelerate, and clear the active and the margin desirable in case of a missed approach. Many airports are not this simple with parallels and taxiways all over the place. IFR departure capacit more a function of the parking areas behind the hold short so one can get a good bunch lined up to go. From the passenger/airline point of view most delays are between the runway and the gate.

with the MLS the receiver has to have a processor also to provide signals for the ILS style cockpit displays (either steam guage or EFIS) This does not use the capabilities available from MLS, such as curved and segmented approaches and data link, butthen again until the procedures and Mk1 Mod 0 pilots are retooled these will not be used anyway.

[walkman]

Lost,

Tekky time...

There are a couple of ways of "doing" MLS. Doppler MLS which the development engineers put on to the "too hard" pile years ago, and Time Reference Scanning Beam which all the current systems use as far as I know.

As you know, ILS transmits two "straight lines" for the aircraft to follow. The localiser uses VHF frequencies very close to the commercial broadcast band and is susceptible to interference from pirate radio stations, as well as the usual airfield obstructions like buildings, taxiing aircraft etc. The Glide slope uses a higher frequency, but is still very sensitive to the local environment.

MLS works differently. For a start the frequency is way high (microwave), up out of everyone elses way.

Instead of a Localiser and Glide slope, you have an Azimuth transmitter and an Elevation transmitter.

The transmitters don't radiate a "straight line" to follow. Instead they scan a beam of microwave radio energy rapidly from left to right of the tranmitter aerial system in an arc up to about 120 degrees

The receiver in the aircraft "sees" the beam go by on its first (left-to-right) pass and starts a timer, it then waits for the beam to return on its right-to-left pass). As the aircraft equipment knows the scan speed, it can calculate its position in the arc and work out an azimuth. The same applies for calculating an elevation using the up-down-up scanning beam information from the Elevation Tx.

This way each individual aircraft can find its way into the runway from any angle in the area of coverage (allowing curved approaches etc)

It also allows fixed wing aircraft on straight in approaches to use the same landing system as helicopter traffic who may be doing their curvy stuff off to the side of the main runway (demonstrated by NATS in Aberdeen back in the early nineties if my memory serves!!)

There are also datalink options to send information up to the flight deck if the airport operator wants to do this (local weather etc.) and some other datalink options for the Military to play with.

Unfortunately, all the best toys are expensive...

Hope this helps. It cleared some very old cobwebs from my head!!

Walkman

[Lost_luggage34]

All great information - many thanks.