Wake Seperation at EGCC

[rich]

I wonder if any of you could clarify your views on the 757.

Last week at EGCC I almost caused a go around, I felt in conjunction with the tower.
We taxied for 24R, down to the end infront of us was a Luthansa CRJ. We were told to line up after him but that we would be 3rd for departure. As we followed on to the runway a 757 was cleared to line up from the intersection infront of us. This was the first point where we could actually see what a/c type it was and had not been previously told its type.

Due to the research in the states and advice from the UK we treat a 757 as a heavy type for wake, and give them 2 min seperation. As it was departing from the intersection it now became 3 min seperation.

We were then cleared immediate take off. We couldn't accept and got a very disgruntled controller saying he wished we'd told him earlier some one on finals. We explained we treated a 757 as heavy and waited. After 2 minutes we were told you've had your 2 minutes go. We waited about another 45 secsand just made it off before finals a/c would have had to gone round.

So do you guys consider the wake problem or is it up to us to advise you, and in which case should it be policy for you to tell us what type we'll be after.

The other point is the classification of the 757. As I say our company policy is to treat it as a heavy for wake but maybe not everyone does.

cheers Rich

[ATC Watcher]

In my centre we treat 757s as heavies and I believe this is now passed ICAO .
But even 6 NM (or 2min) won't be a guarantee for smooth passage. It depends also quite a lot on the aerology (winds, temperature, posssible inversions etc..) of the day.

[ATCO Two]

Hi Rich,

A few misunderstandings to clear up here. In the UK following a considerable amount of research and data collected on the subject, a B757 is categorised as an Upper Medium aircraft. This means that a Lower Medium aircraft such as a B737/MD80 etc needs to be 4 nm behind a B757 on the approach instead of 3nm (or 2.5 nm if approved at the ATC Unit). On departure provided the tracks diverge by 45 degrees or more the separation for a Lower Medium behind a B757 is I minute. If you are not happy with this you must tell the Air Controller before line up to allow for possible resequencing.

Intersection departures. The 3 minute vortex separation behind a Heavy aircraft is only applicable if you are departing from an intersection behind a Heavy from the full length of the runway. (Some intersections are sufficiently close to the threshold to allow this requirement to be waived, e.g., Block 18, 86 and 102 at Heathrow.) Hope this helps.

[55 and a bit North]

rich,

You don't say what type of aircraft you were in, and I echo the above comment, if you are using MORE runway than the guy before you then there is definitely no need to increase the separation, that applies if you start your T/O roll from further along the runway than the one ahead.

(Qualified NATS ATCO)

[cleared4takeoff]

Although alot of Atco's will probably disagree with me on this one, I personally think if you require more than the required UK minima following a 757 then take it. Common sense (and certainly at EGLL procedure) is to state this before lining up just in case of the problems Rich has pointed out. At LL normally it is not a problem save for the few times we have landers on the dep runway but I would imagine at CC,KK etc it could be embarrassing. So many controllers get quite concerned about the waste of runway utilisation etc caused by this whereas until it affects my salary(maybe after privatisation !!) then I couldn't give a hoot.If you think you need it, then take it.
Harry

[PPRuNe Radar]

Agree with most of the above, especially that the pilot's requirements are important. But on the flip side of the coin so is the application of common sense and the need for pilots to be aware of the big picture and how they can help ensure it all flows smoothly and efficiently by passing anything out of the ordinary as early as possible. (Same goes for us in ATC of course)

[rich]

Thanks so far guys,

To clear up a few points we were in a Fokker 100. We departed from full length. The 757 departed from an intersection ahead of us. The wind was light and straight down the slot.

Had we known before line up that it was a 757 we certainly would have spoken up. However as I said before we were told no.3 for dep line up after. Once lined up, and the No.1 departed, the 757 was cleared to line up from the intersection so we'd alredy lined up before we knew ( at MAN we really expected an ATP or SAAB to go from the intersection ) so it would have helped us to have been informed in advance.

The seperation we use for departure are those contained in Pink AIC on Wake turbulence, which is reproduced in our OPS Manual.

Having just re-read the AIC I think our ops manual is in error i.e. if we had departed from an intersecton ahead of where the 757 had gone from, then it would have been 3 minutes however as we were behind only 2 mins, so apologies for the upped heart rates at MAN and thanks to ATCO Two for that one

However as to the 1 min seperation mentioned by ATCO Two I can't find any mention of it in the AIC or our ops manual. The basics say H to M,S,L or M,S to L 2 min or 3 min if departing from an intermediate point on the runway.

Well I've cleared a few things in my mind, including getting our ops manual revised, but am unsure whether we are all getting the spacing from the same source for take off.

cheers rich

[ATCO Two]

Hi Rich,

Regarding the 1 minute separation criterion. This has nothing to do with wake vortex separation and is a departure separation pure and simple. When there are no wake vortex considerations two aircraft can be departed 1 minute apart (i.e. wheels up, next one cleared for take off), when their initial departure tracks diverge by 45 degrees or more immediately after take off. Manual of ATS Part 1 1-19. Might be worth getting hold of a copy of the MATS (CAP493) where all the different separation requirements are listed.
Would certainly echo the above comments; just let us know as soon as possible if you require greater than the minimum separation.