Heathrow Weather

[KelvinD]

Possibly a daft question but:
This morning, Heathrow is suffering from reduced visibility, causing lots of problems for arriving traffic. Virgin & Delta were getting desperate and planning to divert to Birmingham and Stansted respectively.
The inbound Etihad & Qatar flights have gone off to Manchester and the inbound Emirates flight is doing trips around the bay over the North Sea and various other flights are wearing holes in the atmosphere over Ockham.
In this sort of situation, why does the airport not hold departing traffic for 10 or 20 minutes at a time to allow the holding traffic a chance to land?

[HEATHROW DIRECTOR]

Firstly, the poor visibility might be on reason why aircraft cannot land. Second, Heathrow usually operates both runways, one for landing one for take off. Thirdly, in the past departures have been held to allow arrivals to use both runways when weather cleared. However, the use of the departure runway for arrivals is strictly determined by noise abatement procedures. Also, many departures will have allocated "slot" times for departure especially if they are routing over Europe and to miss the slot might cause prolonged delays.

Somebody in current practice will probably give a better answer....

[anotherthing]

Heathrow operates to pretty much capacity when open. That includes runway occupancy and stands. If you let too many aircraft land without letting any/many take off, then congestion on the ground can be a problem.

Also, as in this scenario when you are talking about a morning, airlines want/demand on-time depatures. Despite all the fluffy talk about wanting to save fuel and be green, the bottom line is they would rather an inbound aircraft was held in the stack (and then they would blame ATC), burning fuel, so that they could claim on their statistics that their departure times are adhered to.

This is particularly true of the 'first rotation', where to be a little bit fair to them, you need to ensure that goes smoothly so that the rest of the day runs smoothly.

The knock on effect to the days schedule if you don't get the first rotation away in a timely manner can be huge

[pewpewpew]

I'm on a Virgin having just diverted into Manchester. We were told Heathrow is also on single runway ops. Is this the case as well?

[GlobalJourney]

27R/09L is being resurfaced at night, and therefore does not have a full compliment of lights (no centreline lights, no lead on/off lights etc), and is probably not suitable to use during LVPs at the moment.

[KelvinD]

Many thanks for the responses.
I understand the European slot issues and I also understand the problem of clogging the airport up with queueing departures. But that was why I wondered why this could not be done in, say, 10 minute periods. So 3 or 4 aircraft could be taken out of the queue, then the departures could have 20 minutes or so to play catch up.
Re the work going on on 27R, a couple of smaller arriving aircraft (shuttles) were slotted in so it didn't seem to have affected them.

[Crazy Voyager]

IIRC the BA airbus fleet is fitted with Microwave Landing Systems. This has the advantage in LVPs that the protected area is much smaller, therefore I think the BA airbus fleet is often picked to land on the departure runway in LVPs since that increases efficency.

Some of the heathrow people can probably confirm or deny that as appropriate.

[Talkdownman]

Some of the heathrow people can probably confirm or deny that as appropriate
I suspect that they are gagged by nats...

[Ian Brooks]

No wonder the viz was bad if there were that many nats around

sorry

Ian

[KelvinD]

All the BA landings that day were on the same runway as everyone else and the majority of them were asking for use of the microwave.
Which leads to another question: Why do they have to request the microwave landing? I would have thought that once ATC have given landing clearance, they wouldn't care if they used ILS, Microwave or flags and lamps!

[jpwelton]

They request microwave as it's a different procedure to the others. It usually gets asked for in/approaching the hold so atc know who's doing what approach and the crew can brief and configure the aircraft accordingly. In terms of what it looks like to atc, pretty much the same as an ILS approach. So it guides them to the runway threshold, from anywhere up to around 15nm out, and is approved by Director. They don't get landing clearance until they're inside 2nm, which comes from the tower.

In short, landing clearance comes (a long time!) after clearance to follow an ILS/MLS/Whatever approach.

[twentypoint4]

It's important for us to know which approach is being flown, MLS or ILS, because if either of them unexpectedly fails or gets suddenly withdrawn we then know which aircraft it affects and doesn't affect. There is also slightly different phraseology for the clearances (even know the procedures are pretty much identical.
The previous poster was correct in saying MLS aircraft are normally the contenders for landing on the departure runway during LVP's. This is because the ILS is normally switched off on the departure runway (unless needed for departure guidance in the real pea soup). Also, tower do not need to wait until the departure has passed overhead the localiser at the upwind end of the runway before clearing an MLS aircraft to land, as they would with an ILS aircraft.

[HEATHROW DIRECTOR]

<<Also, tower do not need to wait until the departure has passed overhead the localiser at the upwind end of the runway before clearing an MLS aircraft to land, as they would with an ILS aircraft.>>

I presume that is a new procedure? Given that some departures will cross the LOC at many hundreds of feet I don't understand the restiction?

[twentypoint4]

I presume that is a new procedure? Given that some departures will cross the LOC at many hundreds of feet I don't understand the restiction?

Just repeating what's in the manual. Never fully understood the restriction myself. Perhaps a current LL tower guy or gal can fill us in?

[HEATHROW DIRECTOR]

OK thanks. My brain is so dead I can't remember too much now so apologies if I'm wrong!

[jb5000]

On the A320 during the take off roll there is an automatic pop up of a guidance bar that follows the localiser signal. Can be useful in LVPs if you suddenly lose visual reference.

If you're taking off in a tight gap behind another aircraft in good VMC, as we do at LHR, you can notice this beam bar deviating dramatically when the preceding departure crosses over the top of the localiser transmitter.

I certainly wouldn't want another aircraft passing over the top of the localiser while the autopilot was trying to track the centreline during an auto rollout in 100m RVR.

[twentypoint4]

Or someone from any other airport with an ILS. :ugh:

Of course. But before you go hurting yourself banging that head of yours against a wall, look at the title of the thread and the fact HD and myself were discussing whether HEATHROW procedures had changed.

[HEATHROW DIRECTOR]

jb5000 Thanks for that; very interesting.