Heathrow Approach Path

[DaveReidUK]

I think they call it "thread drift" Gonzo!

"Off-track", so to speak.

[Talkdownman]

After some dodgy bits of opposite-end engineering ISTR we settled for first opposite ender to be at 10D at time of last departure. That's nearer 5 minutes. A good time for a tower handover...

Originally Posted by c52

Why do aircraft fly Biggin-Epsom-almost back to Biggin before lining up with the runway?

This is the classic path-stretch 'dumb-bell' tool to position the downwind traffic in a staggered combined downwind sequence (merging the two down-winds). Have a closer look at Webtrak.

Why do some planes cross the centreline on their approach - e.g. Ockham to ~Edgware?

This another classic tool out of the box when one has too many off the stacks. It also might prevent someone turning back into the hold when they don't really need to. Or if one is in an indecisive or cavalier mood. There weren't too many rules on how to do it back in '93, anything went to make it work. I expect the SMS yellow-jackets have changed all that. But, as HD would agree, it was fun...

[DaveReidUK]

8 minutes? What's going on? When I was there we'd have been shot for that.

In fairness, I should add that the gap between opposite end departures, as opposed to arrivals, appears to average out at around 4 minutes. In fact it's a few seconds less than that in the 12/10 WebTrak example that I quoted.

[c52]

Interesting, and to some extent, less than persuasive. If the whole thing were redesigned today on a blank sheet of paper, would the result look broadly similar or rather different? (Assume LHR doesn't get redesigned).

[DaveReidUK]

Interesting, and to some extent, less than persuasive.

I don't see anyone trying to persuade you about anything.

If the whole thing were redesigned today on a blank sheet of paper, would the result look broadly similar or rather different? (Assume LHR doesn't get redesigned).

Well knocking it down and starting again (in the same spot) isn't an option. As any newspaper will tell you, the scenarios being considered range from bolting on one (or possibly two) additional runways outside of the current airport perimeter, or starting again somewhere else.

Not really relevant to this thread, but discussed at length here:

http://www.pprune.org/airlines-airpo...-heathrow.html

and here:

http://www.pprune.org/airlines-airpo...rt-london.html

[c52]

I can't have been clear enough.

ISTM a flight from anywhere SE of London should arrive via Biggin, not Lambourne. I don't understand why that shouldn't be the case. I asked "why" and I was told that *is* the case.

And I meant to ask, what if all the ATC were redesigned for today's traffic while LHR stays as it is.

Thanks.

[Navy_Adversary]

When my Eva Airways flight from BKK flies over the Antwerp area heading towards Clacton what freqs would the crew use before contacting LHR approach? TIA

It is 1915 hours arrival and we usually have to hold at Lambourne for 10-15 minutes, sometimes going to a 09L but more often 27L, some great views of dear old London Town if the weather is good, even though it is dark.

[DaveReidUK]

ISTM a flight from anywhere SE of London should arrive via Biggin, not Lambourne. I don't understand why that shouldn't be the case. I asked "why" and I was told that *is* the case.

OK, I understand your confusion.

The following is a gross over-simplification, but here goes:

Firstly, if Heathrow could function with 3 holding stacks instead of 4, it would only have 3 - but it can't, that's why the current 4 stacks have existed for many years.

Yes, it might be more logical for a higher proportion of arriving flights to use BIG instead of LAM, but to understand the reasons you really need to look at the airways structure that feeds into both holds.

If you don't have access to any hard-copy maps, look at skyvector.com and select high-level routes, then find two intersections named LOGAN and ALESO. Again, it's an over-simplification, but those are two of the main "funnel" (not a technical term) points that feed into the LAM and BIG holds, respectively.

Then look at the airways that lead to those funnel points. Very roughly speaking, flights arriving from, or over, Belgium, Germany and all points southeast/east/northeast of those countries will route to LOGAN via the airways marked UL610, UL980 or UP7 and thence to LAM.

Flights arriving from France, or over France from Switzerland, Italy, the Med, etc, will route to ALESO and then to BIG, to hold there if necessary.

Bear in mind also that BIG and LAM are less than 20nm apart, so in terms of the track distance flown on a 5000nm, or even a 500nm, route it makes very little difference overall, so that isn't really a consideration in the distribution of incoming routes between the stacks.

I hope that makes sense. No doubt by now our ATC colleagues will be throwing up their hands in horror at the factors I have omitted or misrepresented, but that's my story and I'm sticking to it.

As well as the charts on skyvector.com, it's worth visiting the NATS AIS website, NATS | AIS. If you click on IAIP, then on Aerodrome Index - Specific, you can find the Standard Approach Routing (STAR) charts for Heathrow/LAM and Heathrow/BIG.

[Gonzo]

c52,

LAM - most long haul flight from the far east and many from hte middle east use LAM. This is mainly due to the great circle routes. Without wishing to appear teach you to suck eggs, a straight line drawn on a two dimensional map does not represent the shortest route; you need to use a globe. Flying from Singapore to London takes you up over Russia and approaches London from the north east.

Also, many flight from northern Europe, Germany, Belgium, The Netherlands etc arrive at LAM. Dover is one of the more busy sectors of airspace, so it doesn't make sense to force everything through to the 'nearest' holding stack; that would just cause undue delays as flow control would result in ATC slot delays. Flows around Europe are designed to be 'spread out' to allow more aircraft to fly. This is not just an LHR issue, it occurs at most major airports in Europe.

[HEATHROW DIRECTOR]

I presume stack switching still happens? That means when there is a lot of traffic offering for a particular hold the STAR is changed and the aircraft routes to one of the other holds which is less busy. This has happened in recent days with traffic from the north re-routeing to OCK. I have known traffic destined for LAM to be re-routed to BIG or even OCK.

Now we have someone asking for frequencies!

[c52]

DaveReid, that is very interesting and I'll have a look at that stuff when I'm not supposed to be working.

I hadn't really grasped that it's only an extra 20 miles to go to one hold rather than another, and they'd probably just have to do an extra loop if they saved those 20 miles.

I do notice planes at Biggin that have crossed the coast north of Southend. It seems to happen most at 1500, which is why I asked about disruption caused by the runway swap.

[Gonzo]

c52,

Have a look here, and you can see the general flow into/out of the SE of England.

http://www.londonairspaceconsultatio...r_Traffic1.pdf

....page 4 onwards. Page 4 shows only LHR traffic, dark blue is outbound, light blue is inbound. You can see the organisation of routes quite clearly, and how they are deconflicted.

[HEATHROW DIRECTOR]

<<I do notice planes at Biggin that have crossed the coast north of Southend. It seems to happen most at 1500, which is why I asked about disruption caused by the runway swap.>>

I haven't been following this thread but noticed your last post. There is no relationship between the runway alternation procedure and the numbers of aircraft arriving from a particuloar direction. The alternation causes no disruption at all as final approach spacing is maintained throughout. A runway change to the opposite end can cause short delays but, again, they should not be more than a few minutes. I say all this with the background of 31 years as a Heathrow radar controller.

Aircraft arrival times are dependent on so many variables one cannot lay down precise details. Wind is a significant factor - a strong wind on final approach can seriously reduce the landing rate and before flow control is established, stack swapping may take place. And a million more reasons....

.

[Wycombe]

An unusual I remember from a few years ago.....a stormy evening with CB's all over the Terminal Area, and a rather inconvenient one right over OCK.

The OCK hold was moved to CPT (Compton)! I live out that way and this was the only time I'd ever seen inbounds stacking over what is usually an outbound/en-route beacon.

[DaveReidUK]

Interestingly, there is provision in the AIP for LHR traffic inbound to OCK to use the hold at OKESI (about 3 miles ESE of Chippenham) during periods of congestion in the London TMA.

The hold is just off the western edge of the map on the STAR plate.

[Peter47]

Going back to some of the earlier posts, does a 5 degree ILS scan cause problems in strong headwinds? I remember the one and only time I got to be on the flight deck for a landing (nearly twenty years ago) and there was a strong crosswind and I it appeared that we came in at an angle of more than 5 degrees to the runway (although that may have been an optical illusion) or do pilots have to rely on a visual approach in such circumstances?

[DaveReidUK]

there was a strong crosswind and I it appeared that we came in at an angle of more than 5 degrees to the runway (although that may have been an optical illusion)

It was indeed an optical illusion. The aircraft travels along the ILS centreline, but in order to do so in a crosswind the direction it points in is offset.

[HEATHROW DIRECTOR]

<<The OCK hold was moved to CPT (Compton)! I live out that way and this was the only time I'd ever seen inbounds stacking over what is usually an outbound/en-route beacon.>>

Yes.. when things get really scary the holds are moved all over the place, often x miles from the hold with ATC deciding which way to turn. It becomes quite difficult for ATC calculating when to bring the traffic on towards Heathrow, especially if the wind is strong. I saw an aircraft attempt to join the Bovingdon hold and he ended up almost at Ockham. I still have the grey hairs to prove it.

[philbky]

That's interesting re the moving the holds. In May 2012 I was travelling SNN-LHR on the 07.30 Aer Lingus flight. We were held on the ground at SNN for 50 minutes due to delays at LHR caused by strong crosswinds (bring back 23!). After a very slow descent compared to normal on that service we turned hard left, away from what I would have expected had we been taking the Ockham hold. I know the area west of LHR well both from on the ground and in the air. The day was extremely gusty with various levels of broken cloud and good visual reference points on the ground. We proceeded to hold in a right hand orbit with various aircraft above and below. There was another stack to the south of us which I took to be the Ockham hold. From sighting Reading railway station, White Waltham airfield and the position of the Thames, I took it that an additional hold had been set up based on Woodley.
We eventually exited to the south south east and joined a stream of aircraft ahead and behind from Ockham at approx 45 degrees, turning left into the stream to come around for an interesting cross wind approach and landing on 27R. The weather abated a little during the morning but we still had a 40 minute hold on the ground on departure to Houston that afternoon in wind which was sometimes gusting at 90 degrees side on to our BA 777, strong enough to rock the aircraft a little whilst waiting for push and enough to solicit an apology from the flight deck.

[wiggy]

Peter

does a 5 degree ILS scan cause problems in strong headwinds? I

What's that?

there was a strong crosswind and I it appeared that we came in at an angle of more than 5 degrees to the runway (although that may have been an optical illusion) or do pilots have to rely on a visual approach in such circumstances?

Ah....there's nothing scanning, in the radar sense..the ILS localiser defines an electronic centreline using a couple of fixed signals. The combination of those two signals is picked up by a very simple non-scanning VHF aerial on the aircraft and decoded by a magic box to give the pilots a left/right/ on centreline indication. It doesn't matter within very broad limits where aircraft is pointing, if you are physically somewhere near the centreline, even if flying through it at 90 degrees, or perhaps even flying away from the airport you'll still get the Left/Right/Centre indications on the Flight Instruments.

Moving to the case you describe, crosswind, yes the aircraft will be pointing off at an angle to the runway but you/or the autopilot still tries to fly (track) along the ILS/runway centreline. As an extreme example the likes of a 777 will autoland, using the ILS, with a crosswind of 40 knots - in that case the aircraft just tracks along the centreline, despite the nose pointing away from the runway by very roughly 20 degrees..(that said, you don't really want to actually touchdown with that amount of drift still applied, but that's a gear/tyre issue rather than a problem with the ILS).

BTW having operated into LHR for over 20 years the ATC pros here are coming up with a lot of "blimey, I didn't know that" stuff - thanks ladies/gents