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zatvorenik
23rd Jul 2006, 11:02
Wots going on ? - Why are Ryanair (B738) crew increasingly asking for two minutes spacing behind departing B752s, - and other crews are catching the bug. Wake doesn't stop them eating up 757s on final approach though.
All seems a bit 'Irish' to me......

haughtney1
23rd Jul 2006, 11:06
Its because a "wake turbulence" upset is more critical the closer to the ground you get...if your visual on approach all you do is adjust your touchdown point to beyond the preceeding 75..and your fine:ok:

Its more critical on departure..simply because your margins are that much smaller:ok:

BOAC
23rd Jul 2006, 11:47
Previous discussion here (http://www.pprune.org/forums/showthread.php?t=129730) and the 757, particularly when heavy, can generate significant wake turbulence. Captain's discretion as always (and you have to hope they will advise you BEFORE you line them up for an immediate:) )

The Jolly Roger
23rd Jul 2006, 16:27
"All seems a bit 'Irish' to me......"

What do you mean by this exactly???? B757's are catagorised as "Heavy" Aircraft when considering wake turbulence. Thats probably why Ryanair AND other operators ask for 2 mins. I'm an ATCO and whenever take off clearence is issued to a medium behind a heavy I think its good airmanship to just caution the medium a/c that a B757 has just departed. I always take into consideration the space a medium may need behind a 757 when deciding whether or not to give clearance to line-up.

BOAC
23rd Jul 2006, 17:30
Roger - that is the problem - if you look at my link it appears that it may only be France that does categorise it so. The latest AIP has it as medium. Many disgree with this and as I said, it is Captain's discretion.

Roffa
23rd Jul 2006, 17:31
What do you mean by this exactly???? B757's are catagorised as "Heavy" Aircraft when considering wake turbulence.

Not in the UK, who decided to class them as Upper Mediums.

Therefore here a 737 (Lower Medium in UK) only requires one minute on departure according to our separation tables (and 4nm spacing on final, not five).

point5
23rd Jul 2006, 18:24
Correct! And the thing that really pi*$es me off... someone lines up, cleared to go and its only then they decide to tell you they want 2 minutes! :}

Talkdownman
23rd Jul 2006, 19:22
Correct! And the thing that really pi*$es me off... someone lines up, cleared to go and its only then they decide to tell you they want 2 minutes! :}So is the minimising of runway occupancy STILL a problem at Heathrow, then, with resultant go-arounds.......?
Something for the Command Course Facilitators to take up with their 'newbie' captains, I feel.........
Perhaps CRM training should touch on the development of 'external awareness', or is that too much to ask?

point5
23rd Jul 2006, 19:29
Nop! No resultant go-arounds unless we are TEAMing as we use one runway for Deps and one for Arrs. Just a bit annoying when you have good departure splits.

terrain safe
23rd Jul 2006, 20:14
I seem to have to argue with pilots all the time to go behind a 757. Some will, some won't, even within the same company, drives me mad, even asked one are you ready for an immediate behind the 757, answer yes, then lines up and refuses to roll. Result same company go around. Bet that was fun in the crew room later. Pilots say that it is company restrictions, well I don't work for your company therefore I don't know these rules, anyway you went a minute behind yesterday. F***ing pilots :ugh::ugh:

throw a dyce
23rd Jul 2006, 21:49
In HongKong we had to give 2 mins vortex behind a 757 for other mediums on departure.
I'm not sure if it's an ICAO requirement or it was just in the HK AIP.757s are nasty things for vortex and if pilots wants 3+ mins behind one,then thats what they will get.After all it's their safety thats the issue.

Talkdownman
23rd Jul 2006, 22:04
Nop! No resultant go-arounds unless we are TEAMing as we use one runway for Deps and one for Arrs. Just a bit annoying when you have good departure splits.er.....I remember it well........especially on SRO............alzheimers not quite set in, yet. ISTR it was usually DLH who sprung the unexpected 60 secs after line-up. Not pro.

The Jolly Roger
23rd Jul 2006, 22:27
Well.....I guess some Ryanair pilots have been scared S***less runnin into the wake of a 757 and decided to spread the word!! I can see why they might. A 757's wake vortices, whether it is classed as medium, upper-medium or heavy, are pretty horrific if you fly into them. I agree that it's pilots discretion. Afterall, they know best!

Jerricho
23rd Jul 2006, 23:13
On several occasions I've been asked if the preceeding was a 757 when it infact was an A321. Guess quite a few drivers round are more than a little wary.

Say Again, Over!
24th Jul 2006, 02:27
In Canada, the 757 is considered a medium when following and a heavy when in front.

A w/t cautionnary is necessary even to a 747 behind a 757. Lately, I've started doing that with A321 although that is not yet a rule.

Pointer
24th Jul 2006, 04:42
well i am a pilot and have had situations like above;

i beleive there is a rule that states that if a Pilot deems it nessecary to have increased separation with preceding a/c; he should advice ATC

before he/she accepts the line up clearance e.g. T/O clearance

Therefore if you guys clear an aircraft and he/she does not act on that clearance while he did line up, make him vacate the runway immediately, that'll teach him for the next time!

Pointer :E

Gonzo
24th Jul 2006, 06:06
Therefore if you guys clear an aircraft and he/she does not act on that clearance while he did line up, make him vacate the runway immediately, that'll teach him for the next time!

Which in my experience usually takes longer than just letting him roll when he's happy, and also might annoy and antagonise the flight crew enough that their minds start to stray from important stuff.

Pointer
24th Jul 2006, 10:11
True, i did not meant it to be first action but you probably know who it was, you might use this as a last resort to get the point across. but the little people in the big plane should think about this, it is important to know IMHO.

(playing a bit the devils advocate here, don't mean to suggest anything unsafe.. :\ )

Pointer :E

Gonzo
24th Jul 2006, 13:59
Sorry pointer, my smiley didn't stick! Mine was also meant to be devil's advocate!

After a while one gets an idea of which airlines are more likely to want two minutes behind a 757. It's not too difficult to either plan for it in one's order, or ask. Of course, when asking, one must phrase the question in a suitable manner. Asking "Do you require two minutes behind 757?" usually receives the answer "yes". The question "Are you able one minute behind 757 to expedite your departure?" has a higher success rate.... :E

GT3
24th Jul 2006, 16:31
Just a bit annoying when you have good departure splits.

You will end up not caring about the lost minutes one day!

hooplaa
24th Jul 2006, 19:07
It's obvious some pilots want one rule and ATC are applying their rules / procedures.

As previously quoted, it's ok for pilots to ask for extra time, no problem, but as happened to me very recently don't bl**dy tell me you want 2 minutes after you have lined up and especially when you know that I'm trying to depart 2 in a very tight gap on visual splits :ugh:
Sooooo glad we don't have miked up VCRs:mad:

Must say this disease has spread recently at my unit as the associated personnel within a certain blue and white low cost carrier have rotated through.

It's just the lack of consistancy that's difficult to grasp. In my example why did the FK100 ahead in the queue take only one minute separation behind his departing B757 and yet the B738 not?
With this being a repeated thread (every year or so) when is action going to be taken by the standards/authorities?

BOAC
24th Jul 2006, 19:20
With this being a repeated thread (every year or so) when is action going to be taken by the standards/authorities - and how are they going to know about it?

At least 4 posts mentioning refusal of take-off clearance since my post #2, so if it that bad, report it? Airlines have Ops Departments. You should have the numbers. Put the two together.

Gonzo
24th Jul 2006, 20:25
Hooplaa,

Action in what regard? To increase the UK vortex separation behind a 757?

How would any authority know such an issue exists unless it's reported? I've never heard of an ATCO filing on a crew wanting to wait two minutes behind a 757.

Of course, then all the UK airlines who are happy to go one minute behind a 757 get penalised.

I'm happy with the current arrangement. I remember a section somewhere in the MATS pt.1 regarding occasions where separation will be increased, and one of the bullet points mentions 'at the request of the pilot':ok:

PPRuNe Radar
24th Jul 2006, 20:40
If ATCOs occasionally get problems behind 757s, wouldn't best practice be to ask aircraft behind them who you think might need increased separation whether they require it or not before line up ?? And to discuss such with your colleagues and peers so it becomes a SOP.

Use your knowledge, training, initiative, and a bit of common sense ;) and all will be well in the world.

Gonzo
24th Jul 2006, 20:43
Hey Mr. Radar, do you have me on ignore? :p

Mind you, you wouldn't be the only one!:cool:

Talkdownman
24th Jul 2006, 20:49
AD 2-EGLL-1-13
Minimum Runway Occupancy Time...........includes......
"Pilots should ensure that they are able to commence the take-off roll immediately take-off clearance is issued."
"Pilots not able to comply with these requirements should notify ATC as soon as possible once transferred to Heathrow Tower Departures Frequency."
Yes, separation standards are minima and may be increased when required. But there is no excuse for not notifying the inability to comply prior to accepting line-up clearance.
ISTR that when I was an LL Tower Sup we had to log every instance when extra separation was requested. ATC Ops would then process the data, identify trends, and take appropriate action. So asking for extra time once on the runway should no longer be happening. No wonder that point 5 gets irritated.

PPRuNe Radar
24th Jul 2006, 21:02
Hey Mr. Radar, do you have me on ignore?

Who said that ?? :)

(PS No :ok: makes note to read whole thread again next time)

Gonzo
24th Jul 2006, 21:14
"Pilots should ensure that they are able to commence the take-off roll immediately take-off clearance is issued."
"Pilots not able to comply with these requirements should notify ATC as soon as possible once transferred to Heathrow Tower Departures Frequency.
Believe me, all of us at LHR can quote the AIP until we're blue in the face, but most of us are more realistic. Hell, half the crews don't listen to the ATIS. We need to work in the real world, unfortunately.

ISTR that when I was an LL Tower Sup we had to log every instance when extra separation was requested. ATC Ops would then process the data, identify trends, and take appropriate action.
You'd be quite welcome to do my Sup duty on Friday and then tell me if you had enough time to log every instance as you describe. You're also quite welcome while you're in to inform our Ops Department that they should analyse said logs. In fact can I watch? Both they, and the Tower Sup, have far more pressing matters to attend to.

NudgingSteel
24th Jul 2006, 22:23
Manchester MATSpt2 states that, in this very situation, with a similar(ish) category aircraft to depart behind a 757, the controller must ask the crew, before lining them up, if they can accept a 1-minute departure interval. Doesn't take many seconds, doesn't cost anything, but certainly helps with a smooth departure order plan and avoids upset on both sides of the R/T.

Talkdownman
24th Jul 2006, 22:42
the Tower Sup, have far more pressing matters to attend to. Like sorting out the breaks...........et ceteraaaaaa

Gonzo
25th Jul 2006, 07:08
Obviously!!!!!!!!!! :ok:

GuruCube
25th Jul 2006, 13:56
In my example why did the FK100 ahead in the queue take only one minute separation behind his departing B757 and yet the B738 not?
I see even better.... I often get ATR72s and Dash8s going straight behind 757s. Yes, to be fair I always ask them as I can see the obvious effects there, but 90% of the time they say yes, even when asked 'Are you happy to depart immediately behind a 757?'!!! (And the Dashes Im thinking of quite often go from intermediate holds too!).
Anywho... regardless of who is the bravest etc. etc. the issue here is that the crews dont tell us in enough time. Certainly when lining up it is unacceptable. I even find it unacceptable when foreign pilots say '757 is a Heavy' to me - Why aren't they knowledgeable on the AIP for this country? What other risks might they experience if they havent read it? (Yes Gonzo, its the real world sadly :( ).
In fact, for the benefit of the crews reading this... many of us get frustrated when, like point5, we are trying to get maximum runway occupancy and the only double gap we have arranged is that one (And we cant send the 757 second in order). Its even worse if there are a load of inbounds and we have given Approach 3nm packs thinking the 2 deps would be gone (Although its only the crews who suffer for it, I still hate the idea of missed gaps and inbalanced delays!).
Whats my point? Well, just to have a look at the hold and if there are any 757s just advise the AIR controller ahead of time. Our gaps are planned ahead (mostly ;) ) and the sooner we know, the better.
For the record, when Im planning, I try to only ever put a 757 first if there is no choice or if its just part of a larger order... :)

GuruCube
25th Jul 2006, 14:04
Oh, and it reminds me of a story...
It was fairly recent, when some of our ATR72 ('Small' vortex category) aircraft started requesting 2mins behind 'Medium' aircraft. According to them it was new company policy. They found themselves, especially in busy periods of same route traffic, being delayed more than others. (Obviously this isnt what we intend to do, but if you have a number of jets on the same route behind, they will either all be delayed or just the ATR...). What then happened is that some would still ask for the companies 2mins, but some would be happy to take 1min, aware that it may cost them time if not (Gonzo's forementioned method of asking was useful here! ;) ). After a few weeks we never heard anything else and they tend to take the 1min as usual again.

(Im not sure if it maybe took a negotiation from ATC Ops to Airline Ops to explain the situation, but something made them drop the idea)

radar707
25th Jul 2006, 20:54
even when asked 'Are you happy to depart immediately behind a 757?'!!! (And the Dashes Im thinking of quite often go from intermediate holds too!).

MATS Pt 1 section 2 chapter 1 page 9 13.9:
"The pilot of a departing aircraft may request a delay in take-off because of the danger of vortex wake from the preceeding aircraft. There is particular danger for aircraft comencing the take-off run part of the way along the runway"

we've all learned the hard way about this one and it's been covered many many many times before. At the end of the day the safest option for planning purposes is to ask anything going begind a 757 is:

"ARE YOU HAPPY TO ACCEPT 1 MINUTE BEHIND THE 757."

If the answer is yes, then you can line them up or clear them for an immediate take off. If no then adjust the departure plan accordingly and ask for a gap elsewhere should it be required.

Our job and the job of the pilots is all about SAFETY, if you or the pilot doesn't think it's safe then it just isn't done.

And yes i work in a very mixed traffic environment with lots of 757 followed by S/M traffic.

bravosierra
28th Jul 2006, 09:36
Roger - that is the problem - if you look at my link it appears that it may only be France that does categorise it so. The latest AIP has it as medium. Many disgree with this and as I said, it is Captain's discretion.

In Germany a B757 has to be treated as heavy as well (in regard to wake turbulence).

Ben

BOAC
28th Jul 2006, 10:44
Thanks for that, Bravo - it looks as if UK is out of line!

Fairfax
28th Jul 2006, 17:32
I have had three wake 'hits' from 757's in the last twenty years. I suppose I have eventually learned from experience; but they were in progressively larger aircraft, the last in an A300 which (when I wear my specs) seems quite a bit bigger than than the culprit.

I do want two minutes behind a departing 757, and a minimum of four miles (preferably five) when following on approach.

This thread obviously started with Stansted, where a few weeks back, as I took off, I heard a Thomson 757 query why he was behind me, seeing he was at the holding point (R) before me (at S). The controller replied to the effect that Ryanair guys like a gap when behind 757's and there was a brief conflab about whether medium or heavy etc.

Well, I don't know about different ATC regs (re: 757 wake) in Germany, UK, France or elsewhere. but it seems rather obvious common sense to make clear one's wishes before the ATC man commits to a particular course of action and maybe baulkes someone else by default.

The SOP in my particular LoCo does say that you should not accept line-up unless you are ready - else check first if it is still ok. If I want a 2 Min wake delay then clearly I am not ready, and I should say so or expect, not unreasonably, some unparliamentary language.

The first wake experience I had ,about 20 years ago, was in a Dash 7 (not 8) about four miles behind a BA 757 on finals to LHR. We used to reckon that the sixteen big paddle prop blades chopped up vortices rather well, and were surprised when it got bumpy. We were well surprised when the wing dropped forty degrees plus at 1100 feet. In fact so surprised we didn't even swear.


Despite that I still think propellors deal with vortices better than jets. Conditions permitting, in a prop, it is possible to to fly a 4 degree slope and escape the problem. Controversial stuff or what.

Just as an aside, and a contribution to thread creep, the only problem I have with approaching Stansted is that the first or second London freq may give you a speed to fly (say 300 kts) which then surprises a subsequent controller who asks you to reduce pronto. Well, I have noticed in the last few weeks that the handing-over controller says 'Call xyz and tell them your speed. It seems the problem has been recognised and is being addressed. It's good here isn't it.

Regards all.

BOAC
28th Jul 2006, 20:15
Once again (despite the gainsayers:) ) I have 'Chirped' and asked them to look at the Cat of the 757 in the UK.

Pipin mali
31st Jul 2006, 02:19
Correct! And the thing that really pi*$es me off... someone lines up, cleared to go and its only then they decide to tell you they want 2 minutes! :}

Are you a noob??? Lol, what are you doing here? If an a/c report READY to GO,and you cleared him to T/O and it says that he will wait,considering that preceeding A/C was same or lower wake turb. cat.- Vacate rwy immediatelly!!!

Gonzo
31st Jul 2006, 05:49
Are you a noob???

Errr, no he's not.

Have you read the rest of the thread?

throw a dyce
31st Jul 2006, 08:31
The 757 should always have been put in the heavy cat once the problem was identified (20 years ago).
I'm sure the CAA baulked because it would have had a drastic impact on the movement rate at the flagship Heathrow.BA had nothing but 757s some years ago.Different now that they have been replaced with Airbus.
I treat them as a Heavy inbound and outbound.Ok it's covering your back,but you get skilled at that after 3 years in HongKong.:hmm:

Gonzo
31st Jul 2006, 09:02
Dyce,

Shouldn't have mattered. An exception could have been made. As we all know, the air around the UK's busier airports is different than the air around the rest of the UK. We only need 7 miles Heavy-Light rather than 8, etc etc...:ugh:

throw a dyce
31st Jul 2006, 10:22
Yup, 2 and a half miles down final on a sunny day as well.:ok: Maybe it's the right kind of light or something.ICAO you only need 6 miles for Heavy/Light behind.:confused:
It's not the first time there has been strange classifications.Anyone that ever saw a Chinook knows that it isn't a small.It's horrific.Reckon that the BAA wasted a fortune with snow clearing equipment.Just get that thing to fly down the runway.Now thats a snow blower.
Anyway I digress again.A 744 skipper friend said the vortex off a 757 at LL spacing was enough to bounce a Jumbo around.I think that the 757 should be treated with utmost caution.:hmm:

BOAC
4th Aug 2006, 10:48
I have received this from a source I trust well and offer it (edited) for serious consideration on this topic. The first point being made is that without reports to ATC, or ASRs, you CANNOT expect to get any change in the grading of a particular type, regardless of 'what you think of the CAA'. The second clarifies why we have separation.

If a pilot experiences a significant wake encounter, the appropriate response should be to report the incident to ATC at the time to permit the circumstances to be subsequently investigated. It's not much use making an assertion that the problem has been around for years and yet not acknowledged by the CAA et al, if there is a lack of substantive evidence of the problem as a result of, for whatever reasons, pilots electing not to report such encounters.

There would appear to be a misunderstanding among some of the contributors to the thread as to the purpose of the wake vortex separation standards; these are not to eliminate the possibility of an encounter but to limit the roll accelerations/bank angles generated by an inadvertent penetration of the vortex. The transient characteristics of a wake encounter, whilst being disconcerting for a pilot who might not have anticipated one, are such that they rarely result in roll rates/bank angles close to those considered to be acceptable.


Following my post I have received more information, again edited:

AIC 17/99 (still extant) Para. 6 references the importance of wake vortex reports in that they “allow an assessment of the effectiveness of the current standards in providing a satisfactory level of safety” [my underlining], and explains their use in research and the availability of wake vortex report forms. If you don’t have access to the AIC, the procedure is that if a verbal report is made to an ATSU in the UK a report form will be normally made available to the pilot concerned and, where possible, the pilot of the aircraft believed to have caused the wake. Report forms are also available from the Flight Briefing Unit at LHR. You should also be able to ask your Safety Officer for the forms.

Pointer
8th Aug 2006, 09:39
Reading some comments on why a F100 takes only 1 min and some 738 takes 2 min; Maybe there are different ways these people take a timing?

The correct way: timing starts from the moment of rotation, however my experience is that some people take it from the time they line up... eg that could be quite a bit longer then.

Pointer :E

GuruCube
10th Aug 2006, 11:20
The 757 should always have been put in the heavy cat once the problem was identified (20 years ago).
Erm.... that would enable a neat 1min split behind a 777.....! :}

Im not doubting the effects of them, nor previous comments, but referring back to my previous remarks; 90% of the time its no problem and look at the regular situation with a Dash 8 going wheels up behind a 757 from an intersection. Yet classing it as a Heavy would be a nightmare and could lead to significantly worse situations!
I think we should all be aware it is M+ and of the possibility of extra time needed, and crews should be aware of the minimum requirements in the country they are operating! :)

clicker
11th Aug 2006, 12:43
Albeit taken on an approach but this pictures a good one for the disturbed wake.

http://www.airliners.net/open.file?id=1091105&size=L&width=1024&height=695&sok=&photo_nr=&prev_id=&next_id=