Investigation Into Hold-ups on the approach.

[Dyzo]

Basically for a university assignment we have to perform a presentation, I have teamed up with some buddies and our given topic was

"Investigate the Causes and effects of aircraft being held up for long periods during the approach to major airports."


We already have a few topics covered such as the PNB system, but if anyone with relevent experience could give us a bit of guidance or information, we would be very grateful!


Many thanks


The Team!

[DAL208]

Quite simple really...

Imagine a large car park with only one exit, which leads to another large car park. Everyone from one car park wants to get into the other car park at the same time...however, obviously only one can use the exit at a time.

Holding is created because everyone wants to land at the same time.

[anotherthing]

For a minute there I thought you were talking about a modern day Highwayman...

Then I thought you might be talking about the underwear preference of the Cabin Crew.

Turns out you just want someone to confirm that the airports often run at near capacity

[throw a dyce]

Gaps for departures,vortex wake spacing,bad weather causing increased spacing,varied traffic mix and too much traffic.Fog below landing limits,snowclosed,runway blocked or getting inspected.There you go.Oh and my bad vectoring.:ok:

[bookworm]

Turns out you just want someone to confirm that the airports often run at near capacity

But the more interesting question is why that capacity limit results in tons of unnecessary fuel being burnt in holding stacks rather than either holding on the ground before departure or flying more slowly and efficiently enroute.

[BravoMike]

Wow thats a nice topic...

Reasons, as being said...
Equipment

On the ground
degration of ILS/VOR/etc
Degration while no FLOW CONTROL was installed... (there you have it "bookworm")
unexpected event
Crash
aborted take Off (runway inspection etc)
Blocked frequency on the tower
Tower in reduced mode due to
electrical failure
ONLAN failure (read no more RADAR)
fire
etc...
Lack of personelAll of those points can be seen as a reason of delay... It's ofcourse depending if any flow control was installed or not... If not then Sh*$t hits the fan...


In the Air
Aircraft in distress/emergency taking priority
METEO
Visibility
Winds
Ceiling
Other...
RVR below required RVR due to sudden deterioration of Wx
etc...
Aircraft performing a go around can cause delay, not only to himself but to others inbound to the field.
Blocked frequency/RCF etc
Aircraft reducing while being told to keep a certain speed. (This can cause a big gap in front of him and a pile-up behind him)
RADAR
Late handover by previous sector causing the sequence going wrong (a/c too late to descend ==> holding)
Wrong vectoring...
Loss of a safetynet / RADAR increasing the interval between a/c
In general the idea of flow is to keep us controllers working with a constant flow ( maximum traffic without holding), but any one of the abovementioned parameters will influence this and can cause tremendous delays...

If you want more ... just tell me :O

[anotherthing]

Bookworm - there will always be holding.

Being held on the ground before departure is OK for short flights, but not for medium to long haul flightsd - too many variables en-route.


flying more slowly and efficiently enroute. won't work if everybody does it!! There was a 270Kt trial for A/C inbound to LTMA traffic recently.

Complete rubbish because all it did was made the same aircraft turn up to the holds in a bunch, just a couple of minutes later than they would have normally.

You need speed differentials to prevent holding. Yes, sequencing could be done from further out - NATS are developing equipment thta will give the EAT of every A/C inbound to LTMA airfields - this may help en-route to stream them more efficiently for TC (by the time A/C hit TC airspace, there is little time/room to stream effectively).

However the problem will still exist to an extent as AC get the A/C late (and the very fact that UK airspace is actually pretty miniscule for what it achieves).

Similarly, different AC sector groups control A/C inbound to the same hold, but you can bet they won't consult each other about streaming 3 or 4 flows into one, because they have not got the time.

Some improvements are possible, but your answer is too simplistic. In theory, a good idea, but to achieve it...


BravoMike

idea of flow is to keep us controllers working with a constant flow ( maximum traffic without holding)
Not quite correct, there is a mismatch between aircraft efficiency and ATC efficiency. To ensure that a runway that is in almost constant use e.g. Heathrow is used to maximum capacity, there is a need to have some aircraft in the hold, usually planning on Heathrow to have just under 10 mins holding. This gives the Director the flexibility to optimise runway utilisation.

Obviously when something happens to that runway, for example as mentioned in your very good post, then holding starts to increase hugely.

On Normal dyas, flow worksto a degree, but putting measures on to counter say, an incident, take time - and are only really effective for short haul flights... everything else is already in the air and inbound!!

Saying that, the message could be passed down th eline to external agencies to slow things up for us, but that does not always work, as they either want to get rid of traffic ASAP, which means getting it our of their airspace, or they have their own issues to deal with i.e. it is just to difficult.

[bookworm]

Some improvements are possible, but your answer is too simplistic. In theory, a good idea, but to achieve it...

I asked a question, I didn't offer an answer. Even so, I'm intrigued by your negativity. Good job Wilbur Wright was a bicycle engineer and not a bicycle traffic controller. ;)

[anotherthing]

Not negative, just realistic about what can be achieved in the LTMA!! As a TC controller I would love to have a bit more of the streaming done earlier on and correctly for what will happen at the end, i.e. on the runway. However the AC guys don't have the time nor the huge blocks of airspace within which to achieve this.

There can be some improvements, but not to the extent of cancelling holding in normal day to day operations.

If the UK had huge amounts of airspace to allow for lots of track miles, streaming would be better, but it doesn't.

If we can get Functional Airspace Blocks, whereby the procedures routes etc of surrounding ANSPs etc were all tied up togwether, then it would help... can't see that happening for a while though.

[flowman]

First of all Holdings are not meant to be used in a normal circumstances. For some reason London is the only ANSP that consider them as a part of the approach. Trying to sequence A/C from holding patterns could cause major problems in case something goes wrong. We have seen that several times so far. CFMU is giving them 45 A/C per an hour but in reality they are only landing 37 A/C. Somebody mentioned before in one of the chats that London is developing the software to act on the A/C coming from the Europe in order to "stream "them. I have to say that this is exactly what CFMU has been doing for the last 15 years. I have a feeling that CFMU and London should sit down and try to find compromise on how to go ahead in Air Traffic Flow Management for the future.:)

[bookworm]

Not negative, just realistic about what can be achieved in the LTMA!!

And realism is a key part of any process of improvement. I think we're just talking at different levels: you're thinking about what can be achieved with today's systems and structures, and you're right. I was dreaming of a world many years away in which European ATC is a bit more joined up, and information flow (not to mention operator's compliance with procedures!) is an order of magnitude better than today. There may not be an instant fix, but I think Dyzo's project is an interesting one.

[anotherthing]

Bookworm,

you are correct... large scale 'joined up thinking' with all the european states would be needed to make the best go at a decent system... it might happen in the future, but one of the difficulties will be getting countries to relinquish sovereign airspace...

Flowman

the system NATS is bringing in is more along the lines of an extended EAT display, allowing controllers to see what the EAT is for each aircraft and to (hopefully) allow them (the controllers) to issue speed instructions etc that tie in with the EAT, to minimise or negate holding.

The problem could be getting adjacent stand alone sectors talking to each other when they are controlling aircraft inbound to the same hold facility... it could cause more problems for the TC guys instead of alleviating them, time will tell.

If it goes to plan, it will actually be a great benefit.

As for holding in the LTMA - to gain the best and most efficient use of a runway that has over 90% occupancy rates, you need to have a constant supply of aircraft to vector onto final. That is why Heathrow runs best (most efficiently) when it has a few aircraft in the hold.

Remember we are purely talking about the efficiency of runways here, when you have a dedicated landing runway.

[Canoehead]

If you do research on the following:

"Investigate the Causes and effects of cars being held up for long periods during the approach to major cities"

.....you will probably end up with the same core results!

[pax britanica]

Altho a humble pax I think it is worth adding that many major airports delay approaching aircraft but do not use holding as muchas say LHR does. The reasons for this are I am sure those explained here that there is ahuge concentration of aircraft movments in SE England .I belive London as a city has the most air ransport mvements f any city in the world.
Also a very large proportion of the traffic comes from the South or EAst where the airtraffic control boundaries with France Netherlands etc are in terms of the speed aircraft virtually adjacent to the London Terminal Area.

In many other countries the main city is well away from the borders and theres often more space to sort ths out in.

I make ths comment because going to Frankfurt fairly often we fly past the airport at quite a height and contine heading away from t for miles and miles and miles. No holding patern which passengers notice but just a huge detour so ATC can sequence everybody for the runways

Good luck with your project but I think yoare going to find that its no different to the M25 ona friday-two many vehicles not enough space
PB

[bookworm]

As for holding in the LTMA - to gain the best and most efficient use of a runway that has over 90% occupancy rates, you need to have a constant supply of aircraft to vector onto final. That is why Heathrow runs best (most efficiently) when it has a few aircraft in the hold.

There's a clear analogy with manufacturing processes here. 30 years ago, everyone built up huge levels of stock at many stages of a manufacturing process. These days, intermediate parts are produced "just in time", significantly reducing costs. Much of this benefit comes from better information flows within the processes.

To create a constant supply of aircraft to vector on to final, you don't necessarily need holding stacks (stock). But you do need a more joined up ATC system than we have today, with its own form of Kanban.

[Del Prado]

Bookworm, your analogy isn't great. With a dedicated landing runway a 'stock' of aircraft is required to provide the most efficient landing order in terms of wake vortex categories (and keep up the pressure on FIN!)

[bookworm]

Bookworm, your analogy isn't great. With a dedicated landing runway a 'stock' of aircraft is required to provide the most efficient landing order in terms of wake vortex categories

Well gee, I can't think of a manufacturing process nearly that complicated -- just imagine having to process three different sorts of component in a particular order! :rolleyes:

Come on guys, use a little imagination...

[1985]

Too many aircraft trying to arrive and land at the same airfield at the same time. It happens at every airfield sometimes (even the much vaunted AMS) because demand is higher than capacity at that time.

The reason there is always holding at EGLL is due to lack of runway space, lack of airspace to stream in and that it is always operating at close to capacity. One little delay of any sort can cause problems.


Somebody mentioned before in one of the chats that London is developing the software to act on the A/C coming from the Europe in order to "stream "them. I have to say that this is exactly what CFMU has been doing for the last 15 years. I have a feeling that CFMU and London should sit down and try to find compromise on how to go ahead in Air Traffic Flow Management for the future


Sorry if i don't hold out much hope for this. If CFMU were so good at creating a stream for EGLL please tell me how you manage to let 8 inbounds get to the same point at the same time? The only way to create a landing order then is to hold some so that they can be put into stream the correct distance apart. I know flow is and can be a inexact science but surely letting an hours worth of traffic turn up in the first 20 mins of that hour shows theres something wrong?

The new software for the LTMA will only be a good as the people using it. What happens if the kit tells me that ABCXXX should be infront of BCDXXX and its physically impossible to do that?

[anotherthing]

1985

even worse - don't know what sector you work, but how is it going to work when you have two totally stand alone sectors (23 and 22) sorting out between them an order for say the OCK stack - they would have to be constantly in communication with each other!!

Constantly second guessing each other will not work - as if you had the time for it anyways!!

[Gonzo]

I think 1985 might try to work Clacton at some point :E

[anotherthing]

one sector feeding to one hold... if only the rest were so simple (not that I am saying that CLN is simple).

Gonna be bad enough for a heavy RT loading sector such as CLN or TC East to get things in the order as written down by AMAN, never mind two distinct, busy sectors trying to get it right between themselves.

However, it is just a guide after all... it will hopefully reduce some fuel burn