Instrument Approach Spacing

[Indicating Full]

I'm currently studying for a military sponsored aerospace degree and have some questions regading spacing of aircraft on instrument approaches. I am particularly thinking of Heathrow as they have the "greatest" capability in the UK and far greater than anything in the military. I'm particularly interested in:

What is the minimum spacing on the ILS/MLS in VMC?

What is the minimum spacing on the ILS in IMC for Cat 1,2,3 approaches?

What is the minimum spacing on MLS approaches for Cat 1,2,3 approaches?

I would be interested to see the best case figures but appreciate that capacity is limited by surface movement procedures in poor weather.

Is MLS offering the benefits promised? How many runways are operational at LHR and how many inbound a/c are fitted with MMR.

At what point do a/c normally get cleared ot land in the above scenarios?

Apologies for the large list of questions. The topic was discussed at length on pprune and the BBC during the poor weather in December but was lacking some detailed performance figures.

[Il Duce]

"Heathrow have far greater capability than anything in the military". Put your hard hat on, Indicating Full, you may be receiving some flak from the military Directors out there.

[Del Prado]

What is the minimum spacing on the ILS/MLS in VMC?


3 miles. But that can be reduced to 2.5 if there's a good headwind and the runway's dry. Giving a landing rate of 40-48 per hour depending on wind gradient between 4000' and the ground.

What is the minimum spacing on the ILS in IMC for Cat 1,2,3 approaches?

6 miles in LVP conditions. Giving a landing rate of 28.


What is the minimum spacing on MLS approaches for Cat 1,2,3 approaches?

We don't use MLS at the moment.

Heathrow has 2 runways, one for departures and one for arrivals however mixed mode is being discussed which would mean both runways used for arrivals and departures. Theoretically lifting (and stablising) the movement rate.

What's MMR?

[HEATHROW DIRECTOR]

Il Duce.... The RAF haven't got enough aircraft to get a sequence going so no chance of flak.

MMR=some sort of vaccine. ATCOs get it before they start validation training - it melts the brain!

Indicating Full - very best of luck with your degree. Just to add to Del Prado's excellent notes..... at large airports, VMC conditions mean very little as the vast majority of aircraft carry out instrument approaches irrespective of the weather an in Class A airspace VMC conditions may not be used for separation. However, when mixed mode is in operation (sometimes early morning at Heathrow), separation between aircraft on different runways may be reduced if the pilots can see each other and certain other conditions prevail.

[vintage ATCO]

What's MMR?

Multi Mode Receiver - ILS/MLS/GPS in one box. I think BA have some fitted, dunno about anyone else.

[JustaFew]

What happened to the MLS trials at Heathrow during the late 80s and early
90s?

[HEATHROW DIRECTOR]

JustaFew.. I was there (a they say!) and don't recall any thing of a serious trial. I think one or two BA aircraft were fitted and there were procedures laid down but I don't racall ever seeing an MLS approach. Wasn't the whole shooting match abandoned?

Big problem with such things at a major airport is integrating with the "normal" procedures - like the cock-up of the Concorde "Standard Approach", for which a BA F/O made a lot of lolly. But the crews soon realised that a radar approach was the best option - and presumably pilots of other aircraft felt the same.

[Indicating Full]

Thanks for the replies - some useful gen there.
Il Duce,
I'm happy to take the flak - I have been in the military for 18 yrs and have spoken to a few controllers as part of my MSc research - that was not clear from my first post. I wouldn't dare state that civvie controllers were better than military - merely referring to the fact that MLS/LVPs and Cat 3 approaches are something we might experience when we go on our holidays and not in one of our aging aircraft.
I am aware of the multipath propagation issues which require increased ILS spacing in Cat2/3 operations. MLS manufacturers state that because multipath propagation is not an issue they can support reduced separation - presumably back to the 3 miles mentioned previously. Press sources reveal that many of BA's fleet have been vaccinated with MMR and can make use of Heathrow's newly installed MLS and keep the passengers happy - just like they did before Xmas.
I understand that Heathrow signed a contract for 4 MLS installations a few years ago but the docs I looked at seem to indicate that only one is available. I would however, be interested to hear why they are not being utilized.
I appreciate this capability is academic for the military. The only time we might need to recover so many aircraft in a hurry is if the Red Arrows went IMC in the middle of a display.
IF

[normally right blank]

I believe the Space Shuttle is using MLS? But I can't understand how "ordinary" controllers could benefit from MLS?

[heathrow, easy life]

MLS is being tried at the moment with one airbus fitted out, unsure if it will help the landing rate.

[RTB RFN]

Del Prado and HD, for my info and perhaps to assist IF,

Do you expand this/apply Wake Turbulence separation?

[HEATHROW DIRECTOR]

RTB RFN.. At major airports VORTEX separation is provided in the approach by radar separation based on the weight of the aircraft. Different countries have slightly different weight categories but it's basically Heavy, Medium, Small, Light and the distances vary from a basic 3nm out to 8nm for a light aircraft behind a heavy. On departures, timing is usually employed again based on the weight category.

[atce]

I believe an Airbus 320 was due to be doing some MLS approaches at Heathrow yesterday but it was postponed due to Easterly Ops. May be done today if 27's are in use. BTW there are 2 MLS installations currently at Heathrow, one for 27R and the other for 09R.