Morning ATC slots into Heathrow

[Doug E Style]

OK, I know the issue of CTOTs has appeared here before but despite searching, I've not found anything yet relating directly to the following so hopefully some clever ATC people will be able to shed a bit of light here. I've been flying into Heathrow frequently for about a year now and thought I had a reasonable idea of the principle of CTOTs (ie. to absorb holding delays on the ground in this case). However, something happened recently that has puzzled me. On three consecutive days I was operating our company's first flight of the day into Heathrow from another major European airport and each day we were given a CTOT due to Heathrow inbounds (there were no weather issues on any of these days) which amounted to a delay of between 20 and 30 minutes over the three days.

On the first day we were allowed to take off 5 minutes ahead of the CTOT and we held for eleven minutes.
On the second day we took off 2 minutes after the CTOT and we held for thirteen minutes.
On the third day (due to congestion at the departure field) we took off 10 minutes after the CTOT and we held for 15 minutes.

Now, I appreciate the complexity of managing air traffic and the dynamic nature of the business but from these events, it seems to me that there is a very wide time margin involved here. Whether we hit the slot, were early or late does not seem to have made much difference. Had our slot been ten minutes later in each case above, would our holding have been reduced by ten minutes also? I suspect not.
I am not criticizing anyone here; I have immense respect for the UK's ATCOs but I would like to understand the system a bit more than I do at present.

Thanks.

[GT3]

OK, I know the issue of CTOTs has appeared here before but despite searching, I've not found anything yet relating directly to the following so hopefully some clever ATC people will be able to shed a bit of light here. I've been flying into Heathrow frequently for about a year now and thought I had a reasonable idea of the principle of CTOTs (ie. to absorb holding delays on the ground in this case). However, something happened recently that has puzzled me. On three consecutive days I was operating our company's first flight of the day into Heathrow from another major European airport and each day we were given a CTOT due to Heathrow inbounds (there were no weather issues on any of these days) which amounted to a delay of between 20 and 30 minutes over the three days.
On the first day we were allowed to take off 5 minutes ahead of the CTOT and we held for eleven minutes.
On the second day we took off 2 minutes after the CTOT and we held for thirteen minutes.
On the third day (due to congestion at the departure field) we took off 10 minutes after the CTOT and we held for 15 minutes.
Now, I appreciate the complexity of managing air traffic and the dynamic nature of the business but from these events, it seems to me that there is a very wide time margin involved here. Whether we hit the slot, were early or late does not seem to have made much difference. Had our slot been ten minutes later in each case above, would our holding have been reduced by ten minutes also? I suspect not.
I am not criticizing anyone here; I have immense respect for the UK's ATCOs but I would like to understand the system a bit more than I do at present.
Thanks.

I'm afraid I doubt there is any rhyme or reason to flow into LHR. I guess that most of the day they put more planes in per hour than can actually be accomodated. Then when you arrive there is ground congestion.

[Gonzo]

The CTOT, although a definitive time for planning purposes, is acutally a window of CTOT-5 mins to CTOT+10 mins. With this in mind it's easy to see that of, say, twenty aircraft inbound to LHR with slot times spread out over 30 minutes, if ten aircraft get airborne at the back end of the slot window, and another ten get airborne a the CTOT-5 end, you might end up with 20 a/c arriving at the stacks in a very short time.

Also bear in mind that the landing rate at LHR is dependent on the traffic mix. If there's a declared capactiy of 42 per hour, and a lot of them are heavies, you might only land 38 in the hour. All sorts of things come in to play. ATFM as it is practiced is a very blunt tool. There is a lot of work going on behind the scenes to try and sharpen it.

[Doug E Style]

Thanks for that Gonzo. Your first point more than explains what's involved here. The second one made me think a bit though; obviously the declared capacity at Heathrow is less with heavy aircraft inbound but given that almost all of these flights are already en route at the point that CTOTs start to be issued, should that not be factored into the equation? In other words, surely someone somewhere knows that of the X number of aircraft inbound, a known number will be heavies? Or am I overestimating the abilities of "the system"?
Also, you mention that much work is being done to improve flow management. Does that mean that a day will come when a CTOT is issued, we take off in accordance with it, no holding at the initial approach fix and a stand is available when we land? That's probably asking a bit much but how close to that ideal is feasible?

[Gonzo]

The flow system at the moment just sees 'a flight', not what vortex category. If the system could be 'tuned' to that level, obviously that would be an improvement. Likewise, at LHR a particular aeroplane's taxi time can vary greatly depending on which terminal (and from which stand within the terminal) it's operating from. 09R for departure, a T1 departure might need a taxi time of 30 minutes if there's a decent queue, but a T3 depature might only need 10 minutes. The system can't differentiate to that level, so we have a compromise of 20 minutes, which means quite a few T3 flights get delayed on stand waiting for the slot, but many T1 flights are delayed because they miss their slot times.

As to your 'dream scenario', I don't think it will ever get to that. The work being done is varied. I've been involved in some of the initial discussions. Some of it is actually just changing each ATCO's way of thinking. Most ATCOs will work really hard to provide the best possible service to the flights under their control. However, when in comes to 'network management', providing that level of service to one flight is actually to the detriment of the network as a whole.

For instance, an ATCO down at LACC Swanwick manages to get a direct routeing for a flight out of northern europe going to Manchester, which saves tens of track miles, and thus time. However, that flight was given a CTOT calculated upon the flight plan route. A/c now turns up early and creates workload at Manchester.

An example that was described to me at a network management conference I attended a while ago (apologies to any CLN or North Sea ATCOs, my memory might have lost a few bits, but you get the idea!): LACC North Sea and CLN had been busting a gut to get direct routeings for EBBR and EHAM transatlantic outbounds that were joining the northbound flow up past Daventry. However, because North Sea was doing (to them) such a good job, the aircraft kept joining the northbound airways just at the point and level where inbounds to EGCC and EGGP etc were descending through, thus creating lots of hassle and very high R/T loading on Lakes. If the aircraft had been kept on the flight plan, they would have joined the nortbound
flow at a different point in a much easier fashion.

This was the reasoning behind the recent '250kts on departure' trial in the London TMA. The more 'standard' each flight is, the more predictable and stable the environment is, and thus flow management becomes more effective.

Ok, it feels as if I'm rambling now, and I'm sure I've probably confused you! I've confused myself! :O

[PPRuNe Radar]

Welcome Doug,

Just another few points to ponder for you ;)

Quite often the CTOT you are issued is not directly related to LHR and may actually be a restriction due to en route capacity issues. Whilst the company Ops people can access what airspace is causing the maximum delay to your flight, it may not always be obvious to the flight deck.

With that in mind, clever people have also worked out that the way to maximise the arrival rate at LHR is to have a reservoir of aircraft in the holds there. This allows the controllers to pick and choose aircraft for the arrival stream without wasting any gaps which might occur if they stuck to and enforced the 'published' arrival rate, given the inaccuracy of this as a blunt tool since the size of the CTOT window and the time which aircraft can gain or lose en route, particularly over long distances, is something which does not lend itself to guaranteeing a smooth and consistently spaced arrival stream.

Your final point is always an interesting one. Technologically, it should be possible for a real time automated system to monitor aircraft all over the globe inbound to LHR (as well as to everywhere else), issue 4D flight path clearances, monitor for compliance, and then issue amended clearances for traffic to operate over waypoints or gates +/- a few seconds. Probably not a big deal to Airbus guys whose throttles don't move, but Boeing guys might get dizzy seeing them move backwards and forwards continually as the speed changes are demanded ;).

One of the main hurdles to this is money since you will have to pay for the development of the kit, provide it to every 'ATC' facility in the world since everyone will have to integrate their local problems with every other aircraft on the globe, and then get operators to equip so they are capable of flying in such a system. Then you have the problem of airlines planning their flights to all arrive and depart at similar times. Regardless of technology, you can still only get one aircraft on the runway at a time (yeah I know ... land after and conditional line ups exist, but you get the point) , or at a given position in a queue taxying for departure or a stand. In other words, although we can tweak the system today and go for some sort of 'free flight' concept in en route airspace 'tomorrow', the terminal areas will remain somewhere where the differences between what is theoretically possible and what is realistically achievable practically, will remain a long way apart for the foreseeable future.

[Gonzo]

the terminal areas will remain somewhere where the differences between what is theoretically possible and what is realistically achievable practically, will remain a long way apart for the foreseeable future.

Final Approach Spacing Tool anyone? :E

[Doug E Style]

Many thanks indeed for taking the time and trouble to respond in such a detailed and helpful manner. I think I'll go and digest all that information in a darkened room somewhere...

[coracle]

Also, if you are operating the first inbound flight of the morning, then you are at the mercy of when the transatlantic and far east traffic decides to turn up. If this is late, then it tends to get caught up with the short haul traffic which appears about 7am local and thus can cause delays.

On the last set of nights, the trans-atlantic stuff was about half hour late because of a weak jet stream and some of the flights who are authorised to land before 6 local were also late from the far east which meant 15-20 minute delays at 6.30 in the morning.

A good start to the day!!

[Lon More]

IIRC, the long range flights, Transatlantic and Far-East, into EGLL are not regulated. They all tend to arrive in a bunch and make a mockery of flow control calculations. Not helped by those of us in Europe givimg direct routings to REFSO from all points East and shavng 5 - 10 minutes off the flight time.

[BEXIL160]

All excellent explanations..... and another thing, did anyone mention The Weather? :uhoh:

Everything tends to go for a ball of chalk when CB activity and weather avoidance become issues. I'm not sure how any ATFM system in the future will cope with the vagaries of weather forecasting. The current system doesn't

Best rgds
BEX :ok:

[30W]

Bex,

Over in the US it's not uncommon to get a re-route abeam New York, or just south of, inbound to Orlando due weather in Florida. The system is being pro-actively managed, and re-routes feed into STARS where the weather is least predicted at your arrival time.

LACC just works like a blindfolded goalkeeper during times of weather, and that method quite rightly at times requires draconian flow measures. If ATC make the plan, based on forecast and real time weather, then I think you'll find pilots comply and are confident in ATC's ability to take them the safest way (as in US). If you let us decide and plan you get what you do now, sectors not realing knowing what will happen, and flight choosing differnt paths for avoidance - drags the whole system down.

I was quite amazed when talking about weather capability for LACC when you were still at LATCC, that the UK were not going to move forward on this issue :( It was a real opportunity to give UK ATC the tools with which to manage weather far more efficiently. Sadly you were never given the tools with which to do so.......

30W

[HEATHROW DIRECTOR]

Wow 30W.. you appear to have considerably more confidence in the weather forecasters than I do after a lifetime in aviation. Ring any two forecasters and get a different story. I planned to visit Farnborough today with family and friends and checked every available forecast... but early today we abandoned the visit based on three out of four forecasts of rain and thunderstorms. As I write (midday), the BBC is now saying "sunny intervals" whilst uk.weather.com is going for a 50% chance of precip and thunderstorms. Metcheck.com covers itself with "intermittent rain"!

I well remember trying to get a surface wind forecast whilst trying to decide whether to change runways at Heathrow - one forecaster promised a predominantly SW wind and 10 mins later another said it would be mainly SE!

UK ATC does it's very best in the circumstances and appropriate action is taken in severe weather but I suggest that there is a very long way to go before day-to-day planning becomes based on weather forecasts. Just imagine if flow control was introduced based on the forecasts for today.

[aMb]

Thunderstorms at Farnbrough now ;)

[chevvron]

Airspace above 3.5A being used by TC to route a/c round cbs, so Farnborough displays are all low level (A380 was anyway and that's the only one that matters!)

[Yellow Snow]

To answer your other question Doug.
Nothing in the world will make sure you get a free stand when you arrive at LHR, not even a medical emergency pan call. It's too congested and us ATCO's never get the big picture of stand allocation that may allow us to be more efficient in our choices when it comes to holding inbound aircraft on the ground, especially with all the ridiculous work in progress at the moment.
While I'm on this, to any european flight crews out there,
ATC at Heathrow do not and are not responsible for stand allocation, also
If the stand guidance isn't turned on don't ask us to do it, we can't. For obvious health and safety reasons this is done on the stand by the dispatcher. It amazes me how many times crews ask us to do this.:ugh:
Rant over but hopefully you'll appreciate a bit of where the ground controller is coming from!!

[Scott Voigt]

Wow 30W.. you appear to have considerably more confidence in the weather forecasters than I do after a lifetime in aviation. Ring any two forecasters and get a different story. I planned to visit Farnborough today with family and friends and checked every available forecast... but early today we abandoned the visit based on three out of four forecasts of rain and thunderstorms. As I write (midday), the BBC is now saying "sunny intervals" whilst uk.weather.com is going for a 50% chance of precip and thunderstorms. Metcheck.com covers itself with "intermittent rain"!
I well remember trying to get a surface wind forecast whilst trying to decide whether to change runways at Heathrow - one forecaster promised a predominantly SW wind and 10 mins later another said it would be mainly SE!
UK ATC does it's very best in the circumstances and appropriate action is taken in severe weather but I suggest that there is a very long way to go before day-to-day planning becomes based on weather forecasts. Just imagine if flow control was introduced based on the forecasts for today.

We have forecasters at all of our centers today and they put out pretty good and accurate forecasts. They also have some pretty awesome tools at hand. Being that we are more concerned about what is going to happen in the next two to four hours, they get this pretty well. As for telling us what is going to happen tomorrow, they are close but not always accurate. We base our flows by what the Center weather folks tell us, and it does indeed help try to move things in a smarter way, (well when central flow doesn't just bung it all up.) we are also doing it much more for sector flows due to weather.

In a fit of "we have to run like a business and save money." the FAA is looking at cosolidating the weather function to just a few sites and then plan on telecoferenceing to figure out what is going on. Not a good idea at ALL!

regards

[HEATHROW DIRECTOR]

Hi Scott.. The bean-counters took over in the UK many moons ago! Heathrow Airport does not, so far as I know, have any professional Met people on site. When I first went there back in '72 there were dedicated Met Observers and a full forecasting office vailable H24, but not any more so that very valuable "loacl knowledge" has been lost forever. So far as I know, no UK civil airport has dedicated forecasting staff any more although I believe that RAF stations still do. UK Civil ATC Centres have never had weather staff so far as I know.. Met observations at many UK airports are carried out by already over-stretched ATC staff. It's a totally ludicrous situation, but that's life....

[BEXIL160]

Last place we had a dedicated weather forecaster was RAE Farnborough (as Chevron knows;) )

I Spent many mornings driving with the forecaster to do "Morning Prayers" at the Experimental Flying Squadron. Him to do the Met Brief, me to waffle on about Royal Flights and NOTAMs. TC did this infinitely better than me!

Back to LACC. As most people know now, there is absolutely no weather information available on the Radar picture that we look at. Can't see line squalls, can't see CBs. All a matter of guesswork when attempting to plan routes.

Now, 'twas (is) the same at LATCC, but way, way back a weather Radar source WAS asked for to be installed at LACC, something you could "ghost" onto the picture if you wanted to..... I think that went into the "Too Difficult to do" bin. So, we're no better off than we were Last Century. Progress? No, I don't think so. :ugh:

Hence the "Draconian" flow measures that are sometimes rightly required.

Confidence in Forecasts? No, I personally don't have a lot. I tend to look at the synoptics and make my own mind up. As for the Upper winds, I'll look at the forecast, and sometime during a shift ask a flight or two what they are actually getting, if the forecast figures don't seem to be in the right ball park.

Best rgds
BEX.

P.S. Found my running order and timings for several Farnboro' shows many moons ago... All nicely produced by TC, and scrawled over by Me. Do you still use "the Clocks?".