Heathrow MLS

[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 LHR

Out 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)