Slot Tolerance Questions

[ghost-rider]

I work in the ATC cell for a major UK airline.

My understanding is that if ( for example ) one of my fleet has a CTOT of 0830z, then they must be a/b by -5 or +10 ( ie between 0825-0840z ).

However I have heard that this 15 min window is purely at ATC discretion only, and is not to be used for planning purposes.

Can anyone clarify please ? :confused:

On a similar tract, we had a situation today at EDI whereas a slot was issued for 0830z, the Capt called for push and start at 0822z, only to be told that he was no5 in the queue, so he wouldn't make his 0830z, and that the company ( ie moi :rolleyes: ) would need to apply for a new slot.

Again, my understanding is that EDI would have requested BRU issue an AIM increasing the taxi time from 15 to say 25 mins due to ground capacity, and then the slots would be adjusted automatically. Failing that, should ATC not have liased with SCATCC / BRU, & got the a/c away in slot order asap ? :(

Please excuse my ignorance, but if you don't ask ... ;)

( edited for grammar )

[ 05 September 2001: Message edited by: ghost-rider ]

[cossack]

ghost-rider
There is an extra 5 minute window but its use is extremely limited. At MAN we are allowed no more than 3 per hour with 15 per day maximum. LHR and LGW may have similar constraints but I cannot quote them. As for other airports this "discretion" may not be available at all.

As to your EDI scenario - Was he number 5 in the queue for departure or for start-up? If it was the latter, he may well have been number 8 or 9 to depart and therefore unlikely to make the CTOT.

I don't know what the taxi time is at EDI but if it is say 10 minutes normally then a start request 8 before CTOT would not be unreasonable. There were probably extenuating circumstances. Someone in the know may well be able to help with the specifics.

As for getting a new CTOT, sometimes its quicker if ATC send the SRR, with the agreement of the Captain of course.

I cannot comment about this scenario at EDI but a phone call can sometimes, not always by any means, get an extra few minutes. Certainly it shouldn't be relied upon. The Slot Police are watching us you know!

We're here to exchange views and information. Don't be afraid to ask anything.

[1261]

I was on duty this morning when this incident took place. Firstly, I would like to say that your captain was very professional in that he didn't get into an argument on the r/t, telephoning us later instead. I wish everyone were as considerate!

There are several issues here. The inbound sector was late onto stand, thereby necessitating a very quick turnaround on your part. We do not allocate the stands; this is strictly a matter for you, your handling agent, and the airport operator. I know that sounds dismissive, but that's how it works. Speak to BAA!

With regard to the CTOT, we do not enjoy the same leeway as MAN on the slot window. Every extension has to be requested by telephone from Scottish, and often we are simply too busy to chase it up if they don't get back to us. We will endeavour to do so if requested, but bear in mind that the AIP does not require us to do so. On the contrary, the AIP clearly states that (ENR 1-9-3) the -5/+10 tolerance is for tactical use by ATC, and not "for a late departure from the apron". Also, (and I will have to look this up) my understanding is that we can only alter the taxy time for future slots, not ones that are already live.

Lastly (and I was not the ground controller in question!), our job is to keep things moving as best we can. The GMC controller would not have refused push and start unless he genuinely believed that the aircraft would miss its slot. We have had several incidents at EDI over the last year where aircraft which have missed their slots have then blocked the departure queue with obvious knock-on effects - hence we are now quite strict on this. Generally the interval between departures at EDI is 2mins (all our SIDs follow the same initial route), so with four ahead in the queue all it needs is one backtracker (I'm sure you're aware of our taxiway problem) and your man has missed his slot before he leaves his stand.

I hope that this is of some use/interest; if you want to get into a more specific discussion, feel free to e-mail me.

[Edited for typo]

[ 05 September 2001: Message edited by: 1261 ]

[U R NumberOne]

Ghost rider,

You are right about the -5/+10 being for ATC planning purposes only. There's nothing more frustrating than an aircraft calling for start having just missed the CTOT but aware we have the ten minutes to get them to the hold and airborne - a situation that places pressure on us = reduced safety.

At the other end of the scale (ready to go but with a later slot) one major operator at our place has lately taken to asking for start to remote hold just so the off block time looks good.

[ghost-rider]

Thanks for the replies everyone.

1261, thanks for the comment re our Capt - that's appreciated.

Also, thanks for the explanation. That clarifies the situation superbly. I ( and the Capt ) genuinely thought that once the CTOT was issued, then it would be valid with ATC in the event of ground congestion, with local ATC getting them away asap, and without the need to obtain a new CTOT.

Anyway, appreciate the reply - hope we haven't ruffled any feathers !

email on it's way.

Best rgds.

[ 05 September 2001: Message edited by: ghost-rider ]

[Spotter]

UR Number one touched on an important point. I think rushing to meet slot times is one of the biggest threats to safety on the ground.

How many times have you allowed aircraft to push & start on the basis that if he doesn't hang around he should just make CTOT+10.

How many times have you then said expedite taxy, be ready for immediate departure etc, and squeaked the aircraft off right at the very end of the slot in a tight gap between inbounds that you wouldn't normally have used.

Now it's all very commendable in a commercial sense. We all know that time on the ground costs money. But let's not lose sight of the prime objective. SAFETY

How many times have you read reports of accidents/incidents attributable in part or in whole to rushed departures? Incomplete checklists, incorrect configuration, level busts & many more.

Sure they are all the pilots' responsibility. Not much comfort after the event though, & all for the sake of a few minutes.

Then there's the scenario where despite best efforts the aircraft just doesn't get to the holding point in time. Or more usually does get to the holding point just in time had there not been an inbound on short final. Now there is the hassle of having to get a new slot & get the aircraft out of the way of all the other departures behing him who you probably held to get him out ahead.

Many UK airports just don't have the taxyways & holding areas to be able to pass other aircraft so you have to waste a departure window getting the aircraft on the runway & vacating further down to hold elsewhere or rejoin the back of the queue.

Slots may help to prevent overloading en-route controllers, but as an airfield controller they are not your friend. Do not be lulled into poor decision making to try to retrieve the situation resulting from the wrong decision to allow push & start in the first place.

Most incidents have several opportunities where those involved could have stopped the chain of events. Recognise the potential danger & you're halfway there. Situational awareness is not just about where your traffic is.

[Grandad Flyer]

I'm not sure if ATCers will agree, but if its looking like being close to push and make our slot time I will usually give ATC a call in good time and ask if the "discretionary 10 minutes" might be available. If its quiet then usually the answer is yes, and they will give me the latest time I may ask for pushback. If its busy I know about it early enough to do something.
Also, I believe you can get an extra 9 minutes on the slot by going through Brussels. Don't know how this happens, only been on the receiving end. This helps LOADS as usually its only a matter of few minutes.

[gul dukat]

Hi Grandad flyer ..I personally have no problems with you asking ...and will do my level best to accomodate it. As for the extra nine minutes from Brussels I must say that that is a new one on me ...but I stand to be corrected .A standing joke here is that we have NEVER seen a ctot improved by a ready message to the extent that I will usually ask for a phone call to be made ..sometimes to extend the slot when it is obvious to me that you WILL NOT make the original..in cases like this the aircraft often is unaware that we have interceded on its' behalf...all part of being customer facing :D

Mines a club class seat !!

[ghost-rider]

URNo1 & Spotter,

I agree completely re safety. - no argument whatsoever From an airline ops perspective though, we are doing our damndest to ensure minimum ground time ( not necesarily from the financial aspect, more from the simple task of keeping the fleet as on-time as possible - important for a schedualed carrier ! ) and maybe the slot we'll hold maybe that bit too tight practically. That's where the crews must step in and say whether they can or can't make the slot safely. If they say no - I'll delay - period. After all, they're the ones in the pointy-end !

Grandad - it's a myth that you can get the 9min extension just by asking. What's probably happened is your ops dept have judged it spot-on tactically, ( some call it luck ! :rolleyes: ) and delayed the flight-plan accordingly. If we're really stuck, & look like we'll get hammered, we may ask BRU for an extension, but that is a rarity.

[ 05 September 2001: Message edited by: ghost-rider ]

[FlapsOne]

Hi guys, this is an interesting topic.

I was that Captain at EDI........and now I'm seriously confused.

I have no choice but to accept all the offerings on this thread but I am left with more questions than when it started.

Europe has this ludicrous slot system that we all have to live with. It's not perfect....it's not even good.....but we seem to be stuck with it. How do they manage in USA?

When I arrive on stand my handling agent might say one of several things to me:

1. "You have no outbound slot"........yipeeee!

2. "You have a slot at (eg) 0830."

3. "Your slot is 0825 to 0840."

4. "You have a slot a week next tuesday".....but that's another story!

What they do not say (nor do ATC I might add) is "...your EOBT is 0822."

So how can I possibly work to an EOBT when I don't know it? I don't know the designated taxi times for all the airfields. I don't see the Slot allocation message. I haven't the time to ring and ask each time I'm issued a slot. The agents rarely know the details! :confused:

Now, a genuine question. How many professional pilots do you honestly think fully understand these regulations? My guess.....less than 20% (and I'm probably being generous).

Now that's not a dig at any of you fine people out there.....it's a dig at the system. Just look above at the slightly differing views/interpretations we already have. Then some airfields have differing restrictions imposed from time to time. How can I possibly know that! It's not always NOTAMed is it? How do my Ops know?

Is the only answer to telephone ops during each turnround to get all the latest info on the airfield/slot that I'm currently experiencing.......then wait for a call back as ops will have to call someone else to get that info for themselves.......meanwhile delaying the decision to board pax or not (depending on the length of the delay of course).

It is my experince that many, even most, european airfields do consider the -5 +10 as a window for the aircraft and, as long as you are ready for departure in sufficient time to taxi for the END of that slot window the life is rosy. I'M NOT SAYING THAT IS THE RULE (although i thought it was until reading the above) I'm just saying that is what happens. If that has been a case of ATC using their discretionary clearance then all credit to them for doing it without me knowing.......I just thought i was exercising my 'rights' under the regulations.

An end to my ramblings now, and thanks to you all for making me a better informed aircraft commander. I just don't know how closely I can possibly work to these limits in the future.......but I'll do my best.

[Data Dad]

Flapsone .. Your EOBT is what the current flight plan says is your departure time. Therefore, your Ops should always know what the EOBT is and they should be able to tell you.

If not, a quick call on the RT to Ground/Tower (depending on where you are) should elicit the required info......

[information_alpha]

to all the above and especially the pilot involved!

I was working Ground today on what would normally be quite a quiet steady day....

Three times a/c called at the time of their slot (all going to Palma - big delays today)

At all times we will use the full 15mins available, that can mean you pushing quite early to be given takeoff clearance so wheels are up at xx.30 ie right at the beginning of the slot or late to have wheels up right at the end.

If we think you are not going to make it, due to late calling for push or traffic situations at the time (which you may not be aware of as the pilot) we have two options, request that you file a slot missed msg with BRU OR we can call scottish for an extra few minutes. The second option is basically a favour to the pilot by no means is a right a often does not work.

All the time i have been at my unit the nominal taxi time has been 10 mins. Therefore the a/c should be requesting push ten minutes before the specific slot time issued by BRU (and be clean and ready to push when asking - not always the case!) If this happens i have never known the a/c to miss the slot unless somthing happens outwith our control - radar fail, emergency etc. If the a/c asks any later than this the situation has to be assessed and the decision is final!

Noting all that has been said in earlier replies, i would like to make the following points:

1. I would never risk the safety of an a/c to ensure a slot was made, it is not worth it. If i ask and a/c to expidite taxi i would assume the captain would tell me if it was not possible. I pilot would also have been made very aware before pushing the speed was of the essence and that if he felt he could not do this i would expect him to say. Similarly a gap is a gap, you can either get an a/c to depart in it or not, there is no difference whether it will miss its slot or not.

2. Slots are prolific now at all airfields and now the norm. Why do pilots not have details of the individual airfields arrangements ie taxi times etc? Certainly i would expect the the handling agents/companies would have the information to hand.

3. The pilot above was very professional today. I have had a pilot argue the toss about not being given push as he would miss the slot over the r/t at a very busy time - he was lucky further acion was not taken with all the problems it caused.

[1261]

FlapsOne,

The only time that you really need to worry about is your CTOT (calculated take-off time); this is your "slot", and your handling agent should be aware of the taxi time for the airfield. At EDI, (as far as I am aware) this is currently 15 minutes. Put simply, you should be thinking about calling for push and start 15 minutes before CTOT. As far as ATC are concerned, CTOT is the time at wich you should be at the holding point, ready for departure.

As you will know, the nature of traffic at EDI means that at certain times of day we will go from nothing moving to several aircraft calling for push in a matter of minutes. If you feel that for any reason you cannot be at the holding point at your CTOT, let us know as soon as possible. As I said above, our job is to shift the traffic as best we can, and the only reason you would ever be refused a push and start is because we genuinely believe that you will miss your slot. If we can get you away, we will!

Again, I hope this is of some help - I'm not trying to be dismissive.

[flowman]

In reply to ghost rider's question, yes, the -5 +10 is for ATC use to fit you into the traffic pattern.
For the second question, ATC should look after the slot if you are within 30 mins of departure. However all that means is that they should send an SRR, consequently you may receive a big delay.
Some ATC units will call FMD and request a slot extension by telephone, but if they all did that you would wait hours for a reply.
You are correct in saying that the taxi time supplied to the FMD systems should accurately reflect the actual situation on the aerodrome
but fluctuations occur for all kinds of reasons so this figure is more of an average than anything else.

[ATCbabe]

FlapsOne, as you seem confused about the slot situation at EDI let me put it in plain English for you.
The taxi time at EDI is 10mins not 15mins.
If you have a slot time of 1530 the latest you should be asking for push and start is 1520. This gives you 10 mins to push and taxi to the hold.
Having said that the -5 +10 min window means you can get airborne at 1525 so it is acceptable for you to start at 1515.
This 15min window is for ATC use. It gives us a 15min gap to get you airborne in relation to inbound traffic and it is totally impractable to expect us to get you airborne on an exact min!
1261 was correct in saying that for you to be refused start there had to be a good reason. If there is 5 at the hold thats a delay of 10mins, and thats not taking into consideration any inbound aircraft!
As you can appreciate, EDI has its own unique airfield problems, which can make a rapid build up at the hold, which all has to be considered by the ground controller.
If you are in any doubt as to when you should start to make good your slot when it is busy, then I as a ground controller,am more than happy for you to ask me.
Its no use asking for help when you have 6 mins left on your slot! This not only annoys us but also Scottish and London flow when we go on the phone begging for an extension for you.
I hope this has left you slightly less confused. If not it has probably confused even more! Either way have fun flying to EDI, we do try and help as much as we can!
:rolleyes:

[FlapsOne]

ATCbabe

As the pilot involved on that day, unless i mis-read your tone, you seem to be having a little dig at me - n'est pas? I was not confused by the use of the language at all.

I never suggested that it was the job of ATC to get me airborne exactly to the minute.

My confusion arises from the fact that, as can be clearly seen from this (and other) threads, there are too many slightly differing views on the regulations as they stand.

A controller working at, say, EDI, knows the EDI system inside out and backwards - quite as it should be. The controllers at MAN or LHR etc likewise. Each airfield has their own slight variations on how the rules are interpreted and implemented - probably beacause of local traffic peculiarities.

My point is, how can the flying crews, visiting numerous airfields each week, possibly keep up to speed with all the variations?

You make the point that you cannot be expected to get us airborne to the exact minute of the slot - of course - but we have to be ready either early or exactly on time. 1 minute late and we throw ourselves at the mercy of your local airfield and traffic conditions.

I'm not having a go at anyone - honestly, but this is a very imperfect system that doesn't exist in this format in the States where traffic densities are frequently just as high as Europe.

We, as an industry - not individuals, are doing something wrong.

[ATCbabe]

FlapsOne
Afraid you have totally mis-read my tone!
Let me assure you that I am not having a personal dig at you, infact I was not having a dig at anyone. If it appears that way I do appologise.
I was merely stating what is expected at EDI with regards to slots.
This should be the standard way of dealing with slots, certainly within the UK.
You are correct when you say the system is imperfect, and with the situation worsening around Europe, things are probably not going to improve in the near future. Perhaps it is time that the system is reassessed and standardized!!
This would make everyones life much easier and less complicated. :)

[ERJ_145]

EDI - mmm another UK airport with no entry to the runway at it's full length! Why not put on the atis "A/C requiring full runway length should advise ATC on first contact", this would presumably help in planning. Secondly the ATIS could also advise crews of non standard taxi times, due to congestion etc.

All airlines are under pressure to be on time, so ATC are increasingly going to get push and hold requests. Sad fact of commercial reality!!!!!!!!!

[FlapsOne]

ATCbabe

The events of the last few days have delayed my response.

I accept your comments, but you state,

"....I was merely stating what is expected at EDI with regards to slots.
This should be the standard way of dealing with slots, certainly within the UK......"

I now fully understand the situation at EDI but, I assure you, it IS NOT what is being practised elsewhere in the UK or further afield in Europe. It would be wonderful if it were true. There is, in fact, little consistency from airfield to airfield.

Do I really have to get an individual brief from every airfield I fly to in order to fully comply with 'their system' for dealing with slots in Europe?

If that is the case, we may as well all pack up and go home now!

Maybe it's time for Brussels to issue clear, concise and up to date guidelines for the handling of ATC slots within Europe and have exactly the same rules for everyone.

[1261]

Flaps One,

You are, of course, absolutely correct; these rules should be clear and unambiguous from CFMU, and should be applied in a uniform manner throughout the EU. It is in our interests as well as yours that this happens; it means that crews who do not operate into our particular airfield on a regular basis will know what to expect and plan accordingly.

Unfortunately, at the moment at least, the CFMU system of allocating slots does not allow for the particular constraints of any given airfield. It is, at best, a blunt instrument - we can simply ask for a given number of movements per hour, half hour or quarter. If we request six movements a quarter, CFMU can still issue six slots of the same time - and there's nothing we can do about it.

That's why there are bound to be differences in the way the system is managed. MAN, for example, has a network of taxiways that facilitate change of departure order on taxi, remote holding awaiting slots, "quick" departures from intermediate runway links, none of which are available to us at EDI, hence the rigorous way we stick to the rules.

As customers of the airport operator, BAA, airlines need to make their feelings felt at the highest level. After all, BAA own the airfield, they pay for the infrastructure. We (as contractors) just manage the system as best we can. We have a vested interest in maximising the movement rate at EDI - it's handy for us to be able to quote it when our contract comes up for renewal every five years or so.

Also, a reorganisation of the Scottish TMA is being planned, hopefully to allow us more flexibility on the departure tracks and hence improve movement rate - but don't hold your breath!

As to the suggestion that we put a warning on the ATIS about extended taxi times, slot congestion, etc., this seems like an eminently sensible idea, which I will raise with the powers that be!

[FlapsOne]

1261

Thanks for the informative and constructive reply.

I wish you all the luck in the world in trying to improve this situation.

Let's have a few more senior people from around the system voicing ligitimate concerns and suggestions for improvement to 'the powers that be' and maybe it can be resloved - admittedly not very quickly.

This is our industry guys, it will never be perfect - we all know that, but we should try to make it as perfect as possible shouldn't we?