View Full Version : Flying around in circles
10th Nov 2003, 15:50
as a very frequent traveller into LHR, I have often been held by Euro Control awaiting a suitable slot for TO.
Most of us on board realise that the air ways are busy but what really gets us down is when we are held on the ground for 1 hour only to arrive at LHR and be told to stack for 20 mins.
Surely, when arriving from AMS,BRU,CDG etc it would be easier to stay on the ground on the understanding that you do your "stacking" there and get a straight in (or only once round) when you arrive.
I am sure I probably have an over inflated opinion of ATC's computer systems and its not possible to predict with this much accuracy but if flights (from above) are only 10-15 mins out of our airspace on TO surely something could be done ???
10th Nov 2003, 18:11
You must be the only pax in the world who wants to take their delay at their departure point.
Airlines consistently tell ATC they would rather be in the air going round and round, than waiting to depart. Something to do with pax psychology- the airline has departed on time, and now the delay is being caused by ATC etc. I can also see their point. You can't let the pax wait in the lounge/duty free/bar because you can't get them on the plane when you want to. So they have to sit on the ground, strapped in. This seems to really irritate people, whereas going round and round doesn't. Everyone sits quietly waiting.
Go figure. But it is the airline's choice.
10th Nov 2003, 20:58
I'm sure our flow guys can correct me if I'm wrong, but flow control isn't an 'exact' science. Most slot times have a window (say 5 mins before and 10 mins after for example). Also, while a slot time that has been issued allowing for a flow rate at whichever airport you're arriving at, sometimes the actual physical landing rate isn't the same as the flow rate (taking various things like go-arounds, runway changes, special flights, weather or crap spacing on final approach by the controller), thus a holding situation can occur.
On the other side, you can have a guy sit down and land more jets than have been flowed for the hour, thus no delay. As I said, it isn't an exact science.
And as ferris mentions, delays are always our fault anyway :}
11th Nov 2003, 16:57
It's a long time since I was involved but I'm sure such a facility exists. Certainly, internal services within the UK are (or were?) often held on the ground to absorb delays, which led to some long-haul crews who had been holding for an hour wondering why someone who had just arrived from Birmingham was taken straight off the stack! Although the airlines love to get the planes up there, ATC doesn't share their enthusiasm because it's no fun trying to shoehorn so many jets into so little airspace.
At the opposite end of the stick.. I have often sat at Heathrow Approach with my headset off and no traffic to talk to..... then, when I've asked, inbounds have reported holding on the ground at, for example, Frankfurt, or Oslo, for a "slot" to Heathrow. The problem has been the intervening airspace, not the actual situation at Heathrow. Conversely, traffic sometimes takes off with a "no delay" situation only to be held on arrival.
There are many factors and the situation can change so rapidly - maybe the wind will increase, thereby slowing down the landing rate, and a holding situation rapidly develops. Maybe a runway gets closed for 5 minutes.. maybe bad weather arrives. Maybe a medical emergency causes problems, or some charlie on a photographic flight messes up the traffic sequence. It's all good fun, though!!
Back to my rubber ring and slippers.........
Quite entertaining to sit at work here in the cold north late at night with one RAF C-130 down on the pan with a slot 2 hrs away due to congestion in UK somewhere. Pilots totally pissed 'cause there is not an aircraft in sight. :\
12th Nov 2003, 01:17
Having spent a considerable portion of my flying hours going round the holds at LHR I can only say that the flow control system we have at the moment is clearly lacking. Departing Manchester with no slot and then holding at BNN for 15 minutes is a nonsense. An A320 probably costs around £2500 per hour to operate so holding is a VERY expensive game, there has to be a better way than what we have a the moment.
Save my bacon
12th Nov 2003, 01:35
I think that in a dream world (for approach controllers anyway), everything would be streamed, spaced and no holding required. Does this sound like America?!
I can't see this being possible at the busy London airports due to the points mentioned above, as well as problems with speed diefferentials, not only from aircraft to aircraft, but from sector to sector. I feel that the best laid plans would surely go to waste.
We do, as mentioned, accommodate this on occasion as per the MATS 2 for internal positioning flights. The pilots concerned do seem to appreciate these procedures, but from an ATC point of view it can be a headache fitting these aircraft into a busy sequence as it's not just a question of jumping the stack, but having to get down through the levels of all the holding aircraft, and vectoring round various random holding patterns whilst adhering to all standing agreements in extremely tight airspace.
This is, of course, what we're paid to do, but I don't like to think how complex it would be if there were a large number of a/c who had held on the ground coming straight in vs a large number holding in the air...
12th Nov 2003, 01:53
We do, as mentioned, accommodate this on occasion as per the MATS 2 for internal positioning flights.
Sorry S.M.B. but can you clarify this a little. Any positioning flight I have ever dealt with takes the delay hit on the ground and then is sequenced as such. And, I'm sorry, but could you please expand upon your
vectoring round various random holding patterns whilst adhering to all standing agreements in extremely tight airspace. ?? I know I'm a little thick at times, but could you shed a little light on this please?!
12th Nov 2003, 03:43
but has Jerricho got the record for max number of posts in a minimum amount of time???
Still.....http://www.stopstart.freeserve.co.uk/smilie/bttt.gif (back to the top!!) for this topic.....................
Save my bacon
12th Nov 2003, 05:13
Jerricho - ok I don't think I managed to express myself very well - it's been a long day!
The first point about local MATS 2 procedures was indeed referring to a/c taking the delay on the ground and then coming straight in without holding. I was trying to address norodnik's original point and say that this is a concept which happens on an internal level...however
The 2nd point I was trying to get across (!) is that as an area controller it is not always possible/feasible to present a/c which are not holding (due to taking a delay on the ground) below stack levels.
In this case, if a/c are presented to approach at the top of the stack, is this not sometimes a bit of a headache? I was referring to various holding patterns for various airports (I guess I don't really mean random!). I would have thought that a LL approach controller, for example, may find that having to take a/c from the top of the stack into the sequence may cause unwanted extra workload? Maybe not?
Hope this clarifies - apologies if it doesn't!
12th Nov 2003, 17:19
BL, you know I'm just an over-opinionated Aussie wandering the world.
* Still wonders where does he get those great little smilies?*
SMB, got ya! (told you I'm a little slow at times). Positioning traffic (or priority/emergency traffic) coming to us high can increase workload a little, but having a creative TMA bod can really make life easy. Luckily, as a great deal of our positioning flights are from the surrounding London TMA airfields, they don't really get the chance to get high enough to start mixing it up with stack traffic, or we get co-ord early and "book" minimum stack for them. But sometimes, if it's all going horribly wrong, the hold is the best place for them.
16th Nov 2003, 00:26
You've hit on one of my (many) hobby horses here..
Of course the flow system SHOULD be able to cope with the situation you describe. It SHOULD be possible to take a 30 min delay at BRU or AMS and then fly with no airborne holding. But it rarely happens. There are several reasons:
1) The airlines themselves can be their own worst enemies. As I understand it, they like to push back because they have then technically 'departed' and any subsequent delay is not their fault. On the bad days, to leave the pax in the terminal absorbing a delay is bad PR. Far better to leap into the air and then fly round for 40 mins: "Not our fault, mate. Buy another £5 sandwich..."
2) These days, you can ask the FMS of many aircraft when it expects to be at a certain point, and it will get it right to within a minute or two, allowing for TAS and IAS changes, forecast winds etc. The flow system as I understand it assumes all aircraft fly at their filed cruising TAS from the moment they leave the runway, and has NO wind information in it. Consider a westerly wind at altitude of 100 kts. An aircraft flying into that from Berlin to REFSO will arrive a lot later than planned that one which has taken off from Amsterdam, but the flow system makes no allowance for that.
3) The stack management system is not properly managed to take account of delays taken on the ground. If you sit on the apron for 40 mins when there is 40 mins airborne holding, there is a good chance that you will get another 40 mins as you go into the top of the stack. Daft isn't it?
4) 20 mins holding is considered no delay and it is considered most efficient to have about 10-15 mins airborne holding at LL to allow the best utilisation of the spacings.
Of course things may all have moved on since I last checked, but I think that's how it goes.
17th Nov 2003, 20:49
Firstly, you are not held by Eurocontrol. Eurocontrol operates a centralised flow control process across Europe (in place of the fragmented ones of yesteryear) . The method used is ultimately defined by its member states.
You are held by the departing airport ATC who will not permit an aircraft to start engines too early before the slot time, or if the flight evidently would never have made the slot time (ignoring existing taxiing traffic).
The departure slot is allocated 2 hours before departure. The slot is +5, -10 minutes around the Estimated Off-Block Time, plus a variable airport taxi time (longer for busier airports).
The departure slot is calculated by projecting the proposed flight through all points and areas of its proposed route, and applying a counting mechanism. If the number of flights projected into an area exceeds the flow rate defined by the service provider for that area, then the flight is delayed until it would enter at a time when the count is below the defined threshold. The slot time is the accumulated area delays along all en-route facilities. Thus when allocating a slot 2 hours before departure, based on the expected traffic in a sector which is 3 hours flying time away (i.e. 5 hours from when the slot is allocated) does tend to mean a certain imprecision.
The imprecision comes from the wind (it does not use winds, currently, I think). The amount of departing traffic, and arriving traffic may prevent the flight from departing within its slot. Aircraft do not always follow the planned route. Aircraft may be given short cuts by ATC, or be delayed/accelerated by adverse winds. Aircraft often depart outside their slot times, because ATC lets them.
As for staying on the ground, as others have said, its an airline idea. However, keeping traffic on the ground can block up an airport and consume stands that other inbound flights want to use. I think also, at some airports, they are charged by the amount of time on the stand, therefor leaving a stand is economically viable.
Hope this helps :)
22nd Nov 2003, 22:26
The slot is +5, -10 minutes around the Estimated Off-Block Time, plus a variable airport taxi time (longer for busier airports).
-5 to +10 surely ??? :O
24th Nov 2003, 17:12
Quite right. Finger trouble. Abject apologies. :O
25th Nov 2003, 06:01
Heathrow is generally flowed to have holding traffic of approx 10 mins so there is a constant use of runway capacity. That's the way BAA and the airlines want it run so that's what is done. Currently, due to no terminal control contingency being available there should never be a delay of more than 15 mins. Those who work there everyday know this aint happening and there you have your answer. Flow control dont work proper.