Wake turbulence
 

Quick question for my ATC colleagues

I always thought that a heavy departing after a heavy needed 2 minutes separation. I looked up the Ops Manual and it doesn't refer to the above situation - only light and medium types following behind. Any thoughts?

regards

BBK

In the UK there is no wake turbulence separation requirement for a H departing behind another H.

Depends where you are. In Australia trail separation is 4nm but no timed departure sep.

In NZ it's two mins between heavies off the runway.

From PANS ATM 4444


Departures can be 1 min if diverging on 45 degree paths, or 2 mins if the leading ac is faster (or speed controls in place)

I think the more relevant part of Doc 4444 may be:

And what about SUPERs? Nothing in those documents about that ugly thing.

Spitoon,

That section is also correct. We have to remember that all of these standards are a minimum, and do not stand by themselves.

There have been many issues with timing standard, with the ac running up on the leader, and violating min separation.

So the short of it is, both apply.

Denti,
In regards to the supers, there are references and addenda to the document to account for these, currently I know of A380, B747-8, and B787 all have 10nm min sep.

FlightPath, you are correct that both bits of Doc 4444 apply but I think the OP was asking about WT separation for pairs of departing aircraft using the same runway.

The bit you mention about 'Departures can be 1 min if diverging on 45 degree paths, or 2 mins if the leading ac is faster (or speed controls in place)' is an IFR separation and WT separation minima will have to be applied if that is greater, i.e., if it's a single runway operation, a MEDIUM following a HEAVY will need 2 minutes separation (for WT purposes) regardless of the tracks the aircraft will be following.

My manual reports 2 minutes Heavy behind Heavy, it provides SUPER separations too, 8NM radar the widest one, light following The Ugly

Yes, and IFR separation can be reduced by using visual or radar means.

Denti, in the UK we effectively add 1 minute on to the departure separation for aircraft behind an A380.

A380 followed by H = 2 minutes
A380 followed by anything else is 3 minutes.

No, the MINIMUM is 2 mins,
AND Wake separation MINIMUM still apply.

B763/B738, vicinity Melbourne Australia, 2010 (LOS HF)

FlightPath, I'm a little puzzled about the point you are trying to make - and I'm really not sure that it is going to help the OP (or me) to try and bottom it out.

It is quite true that separation standards are minima and can be increased if a pilot request it or a controller believes it appropriate. So, yes, a 2 minute separation requirement means a minimum of 2 minutes.

However, the separation requirement may originate from a need to establish IFR separation or WT separation. The two are done for different purposes and, generally, it is the more stringent of the two that the controller must achieve. It is important not to confuse the two.

In the absence of a need to establish WT separation, and on a nice day (and assuming that Doc 4444 provisions are applied by the State), ATC could launch two IFR flights within seconds rather than minutes by utilising 'reduced separation in the vicinity of the aerodrome' as Gonzo mentions. When I was operational I did this routinely even with large aircraft. If, however, there was a need for WT separation, then even if the controller can get IFR separation in seconds, the WT separation becomes the limiting factor.

Interestingly, in the UK the term 'spacing' was used with respect to WT requirements in order to distinguish it from IFR 'separation' until a couple of years ago (at which time it aligned with ICAO).

I posted the original question. Thanks for all the answers. I was asking as I was operating out of LHR and departed immediately, in a heavy, behind another heavy. When I say immediate I mean we cleared to take off as the preceding aircraft got airborne! That's not a criticism by the way as I appreciate the excellent service we get from London controllers.

Anyway, we had a mild wake turbulence encounter just as we got airborne. Nothing dramatic but we filed an ASR as per our SOP and that got me looking in our Ops Manual and had me wondering what exactly the rules are regarding separation for wake turbulence as opposed to traffic separation. I suspect the company manual has lifted the rules directly form the relevant ICAO/CAA document for these matters. I suppose the lesson is beware of wake turbulence at all times.

regards

BBK

BBK, operating a Heavy out of LHR you should be aware that you can go 'wheels up', as we call it, behind any other Heavy....if you're all lined up ready to go, this can be as little as 45 seconds.

If you don't want this, then please advise TWR when in the holding area that you require 2 minutes (or whatever you need) behind a certain type....providing that you tell us before you enter the runway, we can work around it.

The worst thing for us is to have someone on the runway cleared for take off and then tell us that they need another minute due to wake turbulence.

A bit like sticking someone on the ILS at 0600 who then says 'but we can't land until 0630'... :rolleyes: A waste of precious runway time.
Needing 'an extra minute' on the runway delays everybody by that extra minute. There's always someone else who will use it if you can't...

Thanks for the explanation.

The original post did not mention any specific airport..and only 2 min separation...so I was trying to point out that there is a myriad of standards, not just 2 mins.

As pointed out, at LHR, DP ac do an immediate turn. This is a scenario gets you to a 45 second departure timing.

Every operation has rules for its specific combination of operating procedures, that have waded through the regulatory quagmire to get to what works for them.

I am curious, back to the original question, how would an operator know, unless a regular, to expect wheels up in 45 seconds behind a heavy?

<<As pointed out, at LHR, DP ac do an immediate turn. >>

How about those that go virtually straight ahead?

I look at this from a wake turbulence perspective. As you are aware, that is what we do, measure wake turbulence for Departures and Arrivals.

There are many variables that effect the departure spacing from an ATC perspective, and many variables from the pilots perspective...

If you and the leader go straight ahead, there is no way you can use 45 seconds, that would take you into WT separation. You can mitigate this, by rotating earlier, but there is little means for ATC to require that from an aircraft.

Even with the turn, the following aircraft must watch the rotation point of the leader, if you rotate afterward, you stand a very good chance of a WV encounter before the turn. If there is a marine, inversion layer, or a headwind, even greater chance.

FlightPathOBN,

Now you're confusing me....

Wake turbulence separation either applies or it does not apply. Currently the direction of turn does not affect whether WTS is applied or not. In the future that may well change with Crosswind ops.

If WTS does not apply, then in the UK the departure separations will be stipulated in MATS Part 1, and amplified by MATS Part 2 which will include means such as the use of the ATM or where specific cases of the use of reduced separation in the vicinity of the aerodrome may apply.

For the UK, operators find the wake turbulence requirements in AIC Pink 72/2010.

Gonzo,

During the course of daily ops, one would expect different minima to apply.
There must be a matrix of 'if-then' scenarios.

On DEP, if there is a crosswind, radar sep may govern, if there is a tailwind, time spacing may govern, if there is a headwind, WT sep will govern.

On approach, ROT governs, then it may be radar sep, time spacing, or WT sep. depending on the conditions.

So, under what specific conditions are you saying that WT applies?