Heathrow MLS

[Kirstey]

Hi,

Is is still just the BA Airbus that uses this? or does the rest of the fleet use the MLS as well now?

ta

[Roffa]

Currently still just the Airbus. Don't personally know if there are plans for other fleets (or airlines) to equip with MLS.

[Radarspod]

which is a shame, as MLS is vastly superior to ILS.

Still, if it ain't broke........ :E

RS

[HEATHROW DIRECTOR]

<<which is a shame, as MLS is vastly superior to ILS. >>

In which way did you mean?

[Rwy in Sight]

SLF here but I recall from a conversation with a former ATC and then Airport director, that MLS provides for a greater flexibility on approaches.

Rwy in Sight

[HEATHROW DIRECTOR]

OK... I'm curious as to how that "flexibility" is achieved?

[NigelOnDraft]

HD...

OK... I'm curious as to how that "flexibility" is achieved?
MLS beams are not distorted to same extent, so protected area(s) are much smaller. So spacing on approach, even in LVPs can be less (5NM v 8NM?), also To to Ldg spacing (I believe ILS needs dpearintg aircraft beyond LOC aerial as arriving is at 2NM, MLS can be dep aircraft "airborne" with approaching at 1NM).

You can also do curved approaches etc.

Of course, seeing those theoretical benefits, and getting the airfeld / ATC system to adopt the reduced spacing in practice, is another matter. As, errrr, being discussed between LHR and one of the larger operators there :confused:

NoD

[chevvron]

Curved approaches might be okay at low use airfields where you only have one aircraft at a time, but Heathrow?!!!

[HEATHROW DIRECTOR]

Chev... That's the problem most potential users don't see. It would be immensely difficult to run an approach sequence to a busy airfield with curved approaches!

Spacing in LVPs doesn't simply depend on protecting the ILS - there's the matter of getting off the runway too.

[On the beach]

"It would be immensely difficult to run an approach sequence to a busy airfield with curved approaches!"

They managed to do it at Kai Tak for many a year. Mind you they were using the predecessor of the MLS - the IGS! :)

[chevvron]

With all due respect, Kai Tak was a 'dogleg' rather than a curve, and you had to be visual before the turn ie before you hit the hillside.
A curved MLS approach would be ideal at Farnborough as all traffic would use the same final approach track (FAT) and it could be designed to keep the FAT outside the Heathrow CTR.
We originally decided this would be the way to go at Farnborough rather than install ILS then replace it after a few years, but then along came GPS and the ILS/MLS replacement programme was forgotten (although we did evaluate TLS which could have given us a dogleg approach).

[On the beach]

Kai Tak was a 'dogleg' rather than a curve

You're confusing Chek Lap Kok with Kai Tak, I'm afraid. Kai Tak had the curved approach sequence flashers which rather gives the game away. 07 approaches at CLK have the dog-leg.

[throw a dyce]

A MLS trial was held at Aberdeen in August 1991 with the CAA,FAA,NATS and Air Hanson.The MLS covered 2 runways from the north,16 with a curved approach,and heli Rwy 23.Also there was an approach to 34.The curved approach to 16 commenced at about 10 miles to the North East with a 45 deg turn on to a 4 mile final.It was interesting sitting up front with the needles centred yet the 727 was in a rate one left turn on to final.This an IMC curved approach unlike Kai Tak which was visual turn onto 13.
As for sequencing other traffic it was quite easy,just like fitting an aircraft on to visual approach.
I thought that the system was fantastic,but here we are nearly 20 years later and......?

[bad bear]

Chev... That's the problem most potential users don't see. It would be immensely difficult to run an approach sequence to a busy airfield with curved approaches!

Spacing in LVPs doesn't simply depend on protecting the ILS - there's the matter of getting off the runway too.

wow, thats not a very open minded view, of course curved approaches could work at busy airfields, why wouldnt they? Things dont always have to be done the same way and change can be even better. Runway clearing times might be able to reduce but that is separate from curved approaches.
bb

[eastern wiseguy]

Is MLS not somewhat outdated?
Surely RNAV is the way to go .It offers all that MLS offered without the associated ground systems

[chevvron]

MLS has only been around since the early 70s, whereas ILS has its origins some 30 years earlier, so which one would you call outdated? Don't forget, airfields are still installing new ILS' when they are supposed to have been phased out about 10-15 years ago.

[eastern wiseguy]

Chevvron...they are both old technologies. They will be replaced by the new kid on the block. You have to wonder why MLS didn't find universal favour though?

[HEATHROW DIRECTOR]

<<wow, thats not a very open minded view, of course curved approaches could work at busy airfields, why wouldnt they? Things dont always have to be done the same way and change can be even better.>>

OK... how do you achieve appropriate separations with aircraft approaching from 4 stacks on curved approaches? You have to take into account landing conditions, wind, weather, wake turbulence separation, time of day and all... and all...

[chevvron]

Some years ago (mid - late 90s) DERA, who had already moved to Boscombe Down, decided to do an MLS demonstration at the Farnborough Air Show. I think it may have been in association with NATS, cos the MLS came from Manchester.
Anyway the ex Farnborough BAC 111 was to be used flying a profile completely automatically from initial approach. They designed the procedure and pattern at Boscombe Down and test flew it there too. We were told it MUST follow the pre-programmed route, but when we saw it, were amazed to see not only did it penetrate the Gatwick CTR, but it passed just west of Gatwick, meaning they would have to stop all departures or arrivals while it was in their airspace! They had designed it for the class G airspace around Boscombe and failed to take into account the fact there was controlled airspace near to Farnborough. Not only that, but final approach was designed as a 4.5 deg glidepath, something which the BAC 111 was not designed for. Then we were told we couldn't cross traffic ahead when it was established on the MLS, nor could we allow a departure ahead, which led to a 'backup' of traffic at Farnborough. Needless to say, the requests to enter the Gatwick CTR at about 6pm were refused and the aircraft ended up going back to Boscombe for its demo flights.

[Gonzo]

The MLS sensitive and critical areas, and the protected ranges, are the same as ILS at LHR.

[PeltonLevel]

how do you achieve appropriate separations with aircraft approaching from 4 stacks on curved approaches?One of these days we will get a system which can do an acceptable job of approach sequencing in complex and variable environments (Honest Guv).

[NigelOnDraft]

Hi Gonzo...

The MLS sensitive and critical areas, and the protected ranges, are the same as ILS at LHROut of interest, how has MLS been sold to LHR ATCOs as "an advantage" over ILS? If any...

NoD

[Roffa]

It was principally sold as allowing an increase in movements in Low Vis. MLS equipped aircraft would be first in line to land on the departure runway (TEAM) as the same protection as for ILS would not be required and MLS equipped aircraft might benefit from reduced delays in Low Viz conditions.

The above has failed to materialise and to date the MLS has offered no additional benefits over the ILS whatsoever from where I'm sitting.

[HEATHROW DIRECTOR]

<<One of these days we will get a system which can do an acceptable job of approach sequencing in complex and variable environments (Honest Guv).>>

Pray, explain further. The existing system achieves the max landing rate so how would you propose to better that?

[Roffa]

The current system may achieve the maximum landing rate, but it doesn't always do so in the most environmentally friendly manner. Being environmentally friendly and saving fuel and carbon emissions are very important nowadays.

MLS though will have little to do with that. PRNAV and its more accurate stablemates of satellite based standards are the future, not MLS.

[safetypee]

As I recall, the UK MLS trials work was split between Farnborough, who had responsibility for the technical signals aspects, and Bedford who looked at the operational (RNAV) aspects using a BAC 1-11 and HS 748.

IIRC the theoretical studies for MLS advantage over ILS at LHR (and MAN) considered reduced approach spacing due to lack of interference / co channel problems, and multiple approach path sequencing (environment).
Intermixing steep approaches (with different/inset thresholds - low noise) was considered for normal / STOL capable aircraft, so too for helicopters, which additionally could use variable / offset approach paths and angles without disturbing conventional traffic.
There were also advantages (mainly environmental) for missed approaches and departure routing.
All approaches were designed for Cat 3.

There were several MLS ground units; a semi permanent facility at Bedford with temporary installations at LGW, MAN, Berne, and Tehran in support of the British bid for the ICAO MLS standard.

[Heathrow Tower]

Out of interest, how has MLS been sold to LHR ATCOs as "an advantage" over ILS? If any...

I think we are still waiting to be 'sold it'.....

It's all very political it seems.

MLS was thought to require less protection, therefore less spacing and higher landing rate in LVPs. Turns out a few years ago that the premise was incorrect, and it requires (well, slightly less, but to all intents and purposes) the same protection as ILS.

To convince BA to install it, it was agreed at a high level that in LVPs MLS aircraft would be able to TEAM (i.e. land 6 an hour on departure runway - the fact that you no longer have to be past the LLZ antenna was touted as a benefit - however, if, as an ATCO, you are cutting things so close in LVPs that an extra 1500m or less is critical, then you've cut it too close anyway!). Therefore, BA can land 6 a/c an hour more than otherwise. BA shorthaul get a great benefit, BA overall and other airlines get a smaller benefit as they are able to use those 6 slots the MLS a/c would have used on the landing runway.

Of course, on both westerlies and easterlies, BA aircraft are possibly the worse you can have landing on the departure runway. Also, the 6 a/c are spread throughout the hour. with his/her eye always on the next lander, the deps controller is now going to be ultra-conservative to avoid things getting too close, and so departure rate drops through the floor. After a few hours of TEAM in LVPs, the airfield has significantly more aircraft arrivbing than departing, departure delay goes up dramatically, and those inbounds end up waiting ages to park on stand. Basically after a few hours the airfield breaks.

If we have to TEAM in LVPs, we should either limit it to 3 spread over the hour, or if the airfield is going to cope, either use ILS TEAM and allow us to pick each aircraft so it is best suited to land on the other runway, or in every hour, use 00-45 for departures, then 46-59 for arrivals. Far easier to manage.

But apparently BA have been promised this, so it's politically unacceptable to change the arrangement. :}

[Ivasrus]

GLS is the future ... no protected area, serves numerous airports within the TMA, flight testing less onerous, and much more accurate (to the point of TDZ pavement failure)