Wake turbulence separatin for HEAVY departures

[Ulises10]

Hi all.
In Spain a HEAVY aircraft departing behind a HEAVY aircraft requires 2 min wake turbulence separation and 3 min if the second one departs from intersection.

How is this in other countries? I'm specially interesested in UAE and Qatar airports.

I've been looking for info on the web but what I found is quite confusing. I hope you know the answer.

Many thanks!

[confused atco]

Here's a clue.
the second one departs from intersection
DOC 4444
Chapter 5. Separation Methods and Minima
A separation minimum of 3 minutes shall be applied between a LIGHT or MEDIUM aircraft when taking off behind a HEAVY aircraft or a LIGHT aircraft when taking off behind a MEDIUM aircraft from:
a) an intermediate part of the same runway

[LookingForAJob]

Here's another....a HEAVY aircraft departing behind a HEAVY aircraft....

ICAO does not specify any runway separation for wake turbulence for a H following an H.

FWIW, the UK (where the rules seems to have go a lot more confusing than when I was working there) says '4 nm or time equivalent' for both full length and intersection situations.

[Gonzo]

Looking,

Yes, and what a farce that was, introducing that change!:ugh:

[PointMergeArrival]

DXB it's reduced runway separation if wx permits, min 4NM or track separation prior to handoff to Radar.

[scifi]

Quote...


DOC 4444
Chapter 5. Separation Methods and Minima
A separation minimum of 3 minutes shall be applied between a LIGHT or MEDIUM aircraft when taking off behind a HEAVY aircraft or a LIGHT aircraft when taking off behind a MEDIUM aircraft from:
a) an intermediate part of the same runway


Grammatically that is a bit ambiguous... Which aircraft is taking off from the intermediate part of the runway... The first one or the second one?


( It might help if they used punctuation; 34 words in one sentence is a bit much.)

[phiggsbroadband]

I think the increased separation (from 2 minutes to 3 minutes.) applies to the second aircraft, if the first aircraft has departed from an intermediate point.


This is because the wake turbulence drifts down the runway in the direction of the headwind. It will take longer to move on, or pass overhead, if the first aircraft has departed from further up the runway.


Maybe further calculations are done if departures are taking place with a tailwind.

[Gonzo]

The increased separation is applied when the following aircraft departs from an intersection; it is assumed that it will rotate closer to the rotation point of the lead aircraft, and therefore a higher chance that the airborne tracks will cross.

[scifi]

Gonzo, I think you have the wrong idea of 'departing'. When an aircraft departs from an intersection, it means he has lined up there, and starts the Take-Off roll from that intersection. The Rotate and Take-Off point will be towards the far end of the runway...
Pilots of lighter aircraft often ask for departure from the most convenient intersection, if their aircraft does not need the full length of runway.


Multiple Line-ups on the Same Runway - SKYbrary Aviation Safety (http://www.skybrary.aero/index.php/Multiple_Line-ups_on_the_Same_Runway)


Given similar types of aircraft, the second aircraft will always be flying under the previous aircraft's wake Turbulance. So you should never cross that turbulence, unless you deliberately try to out-climb the leading aircraft.

[Crazy Voyager]

Gonzo knows exactly what he's talking about.

Wake turbulence floats down, you never want to be under someones wake. If you want to avoid it you need to outclimb them.

This is, as Gonzo has said, why you add a minute if the second aircraft departs futher down the runway than the first one. They come closer to the first aircrafts wake and extra time is added to compensate.

And there is to my knowledge nowhere that does take into account wind for departing wake spacing. Heathrow use time based separation but only for landing traffic. I have a faint memory though of someone who used to be in the RAF saying they would ignore wake spacing if crosswinds where high enough, no idea if this still applies though (if it ever did) and what the rules are for it.


In terms of the original question, in the UK 4 miles or time equivalent is provided between heavy heavy departures. However Heathrow and I think Gatwick are both excempt so there are few places this actually happens (Manchester, Edinburgh perhaps? Stansted?).

[Cough]

Scifi,

I agree with Crazy V, Gonzo does know his stuff!

Take two of the same aircraft types. Both are fitted with exactly the same thrust and operated to the same SOP's. Given that they are flying to different destinations with different assumptions in the takeoff perf calculations and a different load, they aren't going to follow the same vertical path... Take two different types and the equation gets worse! Takeoff flight paths cross, it's the way it is!

[LookingForAJob]

Gonzo, I think you have the wrong idea of 'departing'. When an aircraft departs from an intersection, it means he has lined up there, and starts the Take-Off roll from that intersection. The Rotate and Take-Off point will be towards the far end of the runway...
Pilots of lighter aircraft often ask for departure from the most convenient intersection, if their aircraft does not need the full length of runway.


Multiple Line-ups on the Same Runway - SKYbrary Aviation Safety


Given similar types of aircraft, the second aircraft will always be flying under the previous aircraft's wake Turbulance. So you should never cross that turbulence, unless you deliberately try to out-climb the leading aircraft.I, too, will make it clear to any and all users of this board that in my view Gonzo knows what he is talking about. A simple review of his posts should very quickly highlight that he not only knows the rules but also understands their practical application to different situations.

There is a difference between knowing and blindly applying a rule, and understanding a particular topic sufficiently to discuss the merits of any particular element. This discussion started with a question about a rule - for which there is a fairly straightforward answer. But with this topic, more than many others perhaps, just applying the rules will not guarantee to keep everyone safe. The rules will provide a basic level of safety for many, maybe most, situations, but they will not ensure that a pilot/aircraft will never encounter the wake turbulence created by another aircraft - they will, hopefully and with a fair wind (see what I did there?), prevent a severe encounter. This is why it is important to understand how wake turbulence is generated and how it disperses and dissipates in different weather conditions.

There is a very good UK AIC (http://www.ead.eurocontrol.int/eadbasic/pamslight-1D80E7DE9A9813FA59E543EAFD58355E/7FE5QZZF3FXUS/EN/AIC/P/001-2015/EG_Circ_2015_P_001_en_2015-01-22.pdf) on the topic which discusses separations and, of particular interest, the development of time based separations which are intended to take account of the more rapid dissipation of turbulent vortices in certain wind conditions, and where/how the hazards are created. Should be essential bedtime reading!

[Gonzo]

Awwww. You guys..............:O

[LookingForAJob]

I might want something from you one day.

Now you owe me - and don't forget it! ;)

[Grum]

The OP asked about UAE. The reality in DXB from the flight deck is that separation is almost always one minute! We are medium and get one minute behind heavy. It is tight. We usually catch some wake on the approach as well. If you are not happy with reduced separation, you should say so when requesting push-back, but then I don't know if we would ever get airborne if we did this. :uhoh:

G

[Tower Ranger]

I'm sorry Grum but that is completely incorrect.

At DXB Medium A/C are given the standard ICAO departure vortex wake spacing of 2 minutes behind a Heavy and 3 minutes behind a Super departing from the same point, this is increased to 3 and 4 minutes respectively should an intermediate departure point be used. The time is measured from the moment at which the previous departure rotates and the Controller will factor in the time it takes the following Medium departure to rotate when giving the Take-Off clearance.

The OP's original question related to Heavy following Heavy and at DXB this changes slightly depending on weather conditions. When using Reduce Rwy Separation (RRSM) the first A/C must be at least 2500m down the Rwy and airborne. When RRSM is not able to be used it's one minute which is roughly Rwy length and in either case the second A/C is not transferred to Radar until 4nm separation is achieved. These times and spacings are minimums and will increase if consecutive departures are on same Sid's etc.

Grum, if you require greater than the standard ICAO spacing that we provide at DXB just ask for it before lining up and you will probably depart behind the next medium departure.

[pilot1957]

Tower ranger, you mentioned 'The time is measured from the moment at which the previous departure rotates and the Controller will factor in the time it takes the following Medium departure to rotate when giving the Take-Off clearance.'

Does this mean that if separation is 2 mins and controller estimates that after he gives clearance it'll take following aircraft 30 secs to ack, spool up, then roll to where first a/c rotated he will give it after 90sec?
My instinct is that will be similar to if controller did timing by 2 mins from when first a/c started t/o run. Or will that be very different? Appreciate your thoughts

[5milesbaby]

It is a VERY long time since my aerodrome days, however I remember something like if the preceding aircraft is wheels up at 10:00.29 then 10:01.30 is an acceptable "2 minute" departure interval. Is that still the case or should the book now state "120 seconds" to make it precise?

[Occams Razor]

Wake turbulence departure separations are a strictly 2 minutes = 120 seconds, rather than 61 seconds using the "air traffic minute". Speaking of which - where is the definition of an "air traffic minute" written down? Is it just a NATS thing, a UK thing, or worldwide?

[Gonzo]

pilot1957,

Does this mean that if separation is 2 mins and controller estimates that after he gives clearance it'll take following aircraft 30 secs to ack, spool up, then roll to where first a/c rotated he will give it after 90sec?I can't speak for DXB, but I think that's what TR was saying. That is certainly the case for the UK.

I know that in some areas of Europe, a different method is taken, as you say: The time the first aircraft begins to roll is noted, and then the controller begins to transmit the take-off clearance 120 seconds after the noted time. The theory being that the time taken to transmit, readback, react and start to move should cover any difference in the period between start of roll and rotation.

5milesbaby,

It is a VERY long time since my aerodrome days, however I remember something like if the preceding aircraft is wheels up at 10:00.29 then 10:01.30 is an acceptable "2 minute" departure interval. Is that still the case or should the book now state "120 seconds" to make it precise? The book still says 2 minutes, although the requirement has been 120 seconds as far as I remember. The time marking on paper strips used to be HH:MM which could have lead some to use the 'ATC minute'.

With our EFPS, when the controller selects a strip as airborne, it automatically records MM:SS on the strip, which is very useful for judging the next clearance.

[Eric T Cartman]

Given the precision expected , I've often wondered why stop watches aren't mandatory at the air position. I certainly never saw them in use during my years in the uk

[Tower Ranger]

It's a minimum of 120 seconds (must be in a Nats AIC somewhere) and, yes, the controller estimates the time to roll and rotate but its not rocket science as depending on the type departing anywhere from 25-45 seconds works well.

As wake generation is only considered to start upon rotation thats the time that it's based on. It wouldn't really be the same if you waited two minutes from the commencement of roll due to the take-off runs required for different types/destinations. Eg. a B773 to South America will need a lot more Rwy than a B77f with a light load going to Europe. With the known rotation time you have one less variable to consider and it's easier to be more accurate.

[Talkdownman]

The crew will be timing the 120/180 seconds Wake Vortex Separation on the stopwatch. I'd like a penny for every time I was told 'we need another x seconds'.

[HEATHROW DIRECTOR]

Eric... The Tower positions were equipped with electronic clocks which counted the seconds. Maybe they don't have such luxuries nowadays.

[Eric T Cartman]

@HD
Oh yes, I think most towers have always had that. However, using TR's scenario for example , when the B773 rotates you hit the start button on a stop-watch, all you have to do then is wait for the required interval & away goes the next. No need for mental arithmetic, fiddling the minute - is 30 seconds the minute before or after, that sort of thing. Just one less thing to occupy your attention & let you keep your eyes on the outside world, not your desk :-)

[RAC/OPS]

Eric, we have a timer on our ADC console in Melbourne. Some people use it, some don't.