umbyboy

Can TEAMING aircrafts improve the flow-rate or does just the number of planes that take off increase?

Also, since the non European flights are not regulated, does a flow-rate of 26 mean 26 European flights plus the long-haul ones or 26 in total?

BOH

Regarding fog dispersal techniques, as well as the fuel guzzling WW2 British FIDO system, the French deployed something called "Turboclair" at ORY and (IIRC) an improved system at CDG. I believe they remained in use at both airports until the mid-to-late 70s.

https://trid.trb.org/view.aspx?id=73388

It basically involved surplus jet engines (RR Avons) positioned in pits diagonally along one side of the runway and used the hot gases to create a separation of temperature and dewpoint to increase the visibility.

If you look on Google Earth you can still see the remnants of the concrete pits that housed the jet engines at the end of Rwy 06 at ORY. There are about 15 of them.

Heathrow Tower

Arrival:

One radar controller will be responsible for taking aircraft off the bottom of the two northern stacks, Bovingdon and Lambourne, and another radar controller for doing the same from the southern stacks, Ockham and Biggin, and the subsequent descent of aircraft in those stacks. These arrangements may change when it's quiet (one controller might handle all four stacks) or very busy, (there may be one controller controlling the stack, and another controlling the aircraft coming off the bottom).

These controllers are called Intermediate Directors, INT N and INT S (the technical term for the part of the approach between the stack and the start of the straight in final approach is called the intermediate approach). They will vector and give descent and speed instructions to aircraft from the stacks on to the downwind leg (parallel with the runway, but travelling opposite to the landing direction). Once on rough downwind heading, th aircraft from both INTs will be handed over to Final Director radar controller, FIN, who then issues turn, descent and speed instructions to merge both south and north flows on to final approach.

All three are sat next to each other in the ops room at Swanwick. FIN in the middle, INT N to one side, INT S to the other.

Once on final approach, and the distance between the aircraft that has just intercepted final approach and the aircraft ahead is getting close to the required distance, FIN will issue the final speed instruction (usually 160kts to 4DME - 4nm from touchdown). At this point there's nothing more the radar controller can do, so it's at this point that they are instructed to call the Tower.

Geographically, this can happen anywhere from 5nm to 15nm out, usually it's 7-10nm out.

However, Tower controllers (who also have their own radar screen) must not issue any instruction to aircraft outside of 4nm without first coordinating with FIN.

Departure:
Apart from a very few isolated situations. LHR departures are 'free flow'......Tower does not need to ask any other ATC unit for permission to give the take off clearance. At many other airports the tower controller will need to phone the appropriate radar controller for 'release'.

Let's consider departing LHR 27R - that's departing the northern runway towards Windsor. If there's nothing unusual going on, as soon as I see a northbound aircraft start the turn to the right, I can transfer to radar. This might be about 2nm out on departure.

If it's a southbound departure, it's a bit more complex, as there is the possibility of a missed approach off 27L to think about. What we don't want to happen is to transfer a slow climbing 747 that has just started to turn left across the climbout of the other runway when the aircraft about to touch down then goes around.

So, for a southbound, we keep them in frequency a bit longer, until one or more of the following has happened;
- Departure is above 2000ft and we have verified its radar height display is accurate (in which case we would then stop the go around at 2000ft)
- Departure is around 3nm south of LHR
- The arrival that may be the potential go around traffic has actually landed.

All of the above may also be modified because we should not be handing over traffic to radar if there is less than 3nm between departures, and that's regardless of considering arrivals that may go around.

Hope that is ok to follow! It's more complex in many scenarios, but that's the simple stuff!

Heathrow Tower

TEAM, the practice of landing up to 6 arrivals per hour on the departure runway, does improve flow rate, as it will improve the predicted landing rate. We just need to ensure that we can actually land on the departure runway (the ILS system is not on maintenance, or there are no cranes up that obstruct the approach etc) before we consider the flow rate!

No, a 26 flow rate is in total, so you can see how quickly infra-European flights can get delayed in foggy weather early in the morning when there is a high proportion of 'out of areas'.

Jimmie76

Thirded!

Very interesting.

BAAZ

Fourthed. One of the most interesting and informative posts on FT yet.

LHRATCO

Heathrow Tower I've learnt a lot too!

You should come upstairs more often...

Heathrow Tower

Naaaa, don't want to embarrass myself too much.

Geordie405

This certainly has got to be one of the best posts I have read all year - really fascinating and informative, and thanks for the Q&A session as well.

In terms of the handoff from tower to radar presumably it must be a lot more complicated where you have perpendicular runways (as in SFO or LAS for example) and therefore more operations with the potential for aircraft to fly into conflict with one another? I assume arrivals and departures would need to be staggered to maintain separation in the event of a balked landing or a standard go-around?

Heathrow Tower

Well, one thing to understand in that ATC in the USA is quite different to Europe.

An airport layout like SFO would be operated quite differently in the U.K.

For example, in the US there's something called LAHSO, which stands for Land And Hold Short Operations. This means that where there are two runways arranged in an X shape, when LAHSO is in progress, an aircraft can land on one leg of the X and be expected to be able to stop before it reaches the intersection, in order to allow independent ops on the other diagonal of the X.

BA 'opts out' of being part of this procedure, as do many European airlines.

On a standard (UK!) cross runway airport, you consider a take off or landing clearance on one to block the other, until that aircraft has passed the intersection. So, if using one runway for departures, the other for arrivals....one aircraft lands, and rolls past the intersection of the two runways. You can then, and only then, clear the departure from the other runway for take off, with the hope (expectation?) that the departure would be through the intersection before you needed to give a landing clearance to the second arriving aircraft on the original runway. Local procedures will detail the arrival spacing needed to achieve a gap big enough to allow the departure.

To answer your question, yes, the departure and arrival routes would be designed to avoid conflictions, or at least most of them.

Geordie405

Thank you! I really appreciate the insight and explanation

Heathrow Tower

No problem.

Having read through a few of my posts it does almost sound as if I know what I'm talking about......

Can you tell my standards examiner? ^

Worcester

Many thanks for your fulsome answer to both my earlier question and the other questions on here. It has raised my (already high) opinion of those who keep us safe at ATC.

You are doing a great PR job so may well be worth mentioning in your next review.

Heathrow Tower

Thank you for your kind words.

Mods, is it worth amending the title a bit as we've strayed into a general ATC Q&A from strictly fog issues.

Any other burning ATC questions out there?
And no, there are no stupid questions.

BAW845_Matt

I appreciate this may be out of your frame of reference, but in a LAHSO environment how do they mitigate the risk of an aircraft not meeting its clearance limit due to a long landing/brake failure/other reason?