PPRuNe Forums

Go Back   PPRuNe Forums > Ground & Other Ops Forums > ATC Issues
Forgotten your Username/Password?

ATC Issues A place where pilots may enter the 'lions den' that is Air Traffic Control in complete safety and find out the answers to all those obscure topics which you always wanted to know the answer to but were afraid to ask.


Reply
 
Thread Tools
Old 19th Dec 2012, 21:05   #21 (permalink)

 
Join Date: Dec 1999
Location: LHR/EGLL
Age: 35
Posts: 3,833
FPOBN,

There is either the requirement to separate due to wake, or not. Two Lower Medium category aircraft, such as B737s, do not require any wake turbulence separation, just as a pair of Cessna 150s do not require any wake turbulence separation.

Hence why we have a 2.5nm spacing procedure at LHR where, for non-wake pairs, providing Tower can apply visual separation when the first aircraft reaches 4DME, separation is 2.5nm delivered to 4DME, which can compress to even less than 2nm as the first aircraft touches down.

RECAT1A, where it mentions MRS, does not mean that 2.5nm is the wake turbulence spacing, just that this is the closest aircraft are permitted under radar separation on final approach. If aircraft pairs where "MRS" is specified are being separated visually, there is no radar separation requirement. Would you really expect an A380 to have to have 2.5nm wake turbulence spacing behind a E120? The table even explains that it could be 3nm, and implies that it could be greater....some areas in the UK MRS is 5nm. As this figure varies, it demonstrates that MRS is not a factor in wake separation.

Last edited by Gonzo; 19th Dec 2012 at 21:07.
Gonzo is offline   Reply
Old 20th Dec 2012, 16:47   #22 (permalink)
 
Join Date: Mar 2011
Location: engineer at large
Posts: 1,414
Sorry, but in the FAA world that is exactly what it means.

IF the runway has a 2.5nm MRS, then the min wake is 2.5nm, IF the runway has a 3nm MRS, then the min wake is 3nm. I just went through this at KMEM and FedEx.
The FAA defines min separation as just that, a minimum, measured from threshold to the FAF, or in the case of RECAT, 10nm

Here are the details from FAA RECAT matrix. This is also what is built into ATPA.


and the example...


note minimum 2.5nm sep...

Last edited by FlightPathOBN; 20th Dec 2012 at 16:49.
FlightPathOBN is offline   Reply
Old 20th Dec 2012, 18:36   #23 (permalink)
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 2,999
Quote:
IF the runway has a 2.5nm MRS, then the min wake is 2.5nm, IF the runway has a 3nm MRS, then the min wake is 3nm.
If that's the case, I'm struggling to understand why your graphic has two completely different matrices for wake separation and MRS, with the RECAT value obviously being the higher of the two for the relevant leading/following pair.

Or are you simply using the term "wake" to mean the resulting in-trail spacing, rather than specifically that which is determined by vortex considerations ?
DaveReidUK is offline   Reply
Old 20th Dec 2012, 19:23   #24 (permalink)
 
Join Date: Mar 2011
Location: engineer at large
Posts: 1,414
This is not 'my' graphic, but from the FAA RECAT program currently being used.

If you look at the diagram, there is an asterisk...at the lower left, the asterisk is explained. With the FAA, 2.5nm MRS requires a waiver.
With the FAA RECAT, there is no wake spacing allowed lower than the MRS value.

Note the aircraft diagram included...a B747 following the A306...2.5nm minimum wake turbulence separation.

Last edited by FlightPathOBN; 20th Dec 2012 at 19:24.
FlightPathOBN is offline   Reply
Old 20th Dec 2012, 19:43   #25 (permalink)
 
Join Date: Nov 2011
Location: In the middle
Posts: 41
FlightPathOBN, you certainly have a good argument regarding the "compress" of the 2.5nm on the very final phase of flight.
In ICAO chapter 8, where reduced separation minima based on ATS surveillance is described, the minimum between two acft within 10nm of the runway end is 2.5nm.
This is surveillance (radar) separation.

But I would agree with Gonzo, 2.5nm is not a wake turbulence separation, or at least not described as such. I think the paragraph v) of the chapter mentioned above clearly states that 2.5nm may be used (apllied) when distance-based wake turbulence separation minima do not apply...

I also have a question for Gonzo; Who is speaking to the acft until 4DME, or where is the Transfer of Control point (normal operations, not low visibility) between TWR and the unit doing the approach phase? Do you "negotiate" about the visual final part for the every single acft in sequence and landing?
UpperATC is offline   Reply
Old 20th Dec 2012, 20:51   #26 (permalink)
 
Join Date: Mar 2011
Location: engineer at large
Posts: 1,414
I guess there are two issues here (at least)

First off, this IS the FAA RECAT program, Recategorization of wake turbulence separation... not MRS or other separation, but specifically wake turbulence

As you can see, they have detailed the wake and non-wake related operational issues, BUT for the wake turbulence minima...
the minimum, even between same aircraft is still MRS...

Second, as the mechanics of wake generation and transport are not generally understood, especially in the final phase of flight, with the specific danger zone being one wingspan in altitude, it is lemming talk to bring them that close at the threshold.

Wake encounters are reported by the same people who are held responsible for the encounter? Cant imagine why there are few encounter reports...
FlightPathOBN is offline   Reply
Old 20th Dec 2012, 20:54   #27 (permalink)
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 2,999
Quote:
Note the aircraft diagram included...a B747 following the A306...2.5nm minimum wake turbulence separation.
Sorry, perhaps I'm being obtuse, but I don't see that.

The diagram shows wake turbulence separation of 4nm applied when a A306 (RECAT Group C) is following a B747 (Group B).

But when the B747 is following the A306, no wake turbulence separation applies (RECAT rules same as ICAO), so the 2.5nm (minimum radar separation) applies.

In fact, looking at the wake element of the RECAT matrix, there are no combinations of leading/following category that result in a 2.5nm separation on wake turbulence grounds (nor are there in the ICAO matrix).
DaveReidUK is offline   Reply
Old 21st Dec 2012, 08:10   #28 (permalink)
 
Join Date: Jan 2004
Location: London
Posts: 407
Why cite FAA standards?

UK CAA allows for wake turbulence separation minima to be applied between pairs of aircraft until 4 dme, provided the following aircraft is at same speed (or slower) than lead aircraft when the first passes 4 dme. Not to touchdown.

UK CAA continues to build on a huge database on wake turbulence encounters by encouraging a very healthy reporting system whereby both flight crews and ATC are requested to report on any incident.

This isn't anything new for the UK. Wake turbulence separation to 4 dme (not threshold) has been in place for decades. In my experience, the worst upsets inbound to heathrow have occurred in the initial and intermediate approach rather than final.
Del Prado is offline   Reply
Old 21st Dec 2012, 08:13   #29 (permalink)

 
Join Date: Dec 1999
Location: LHR/EGLL
Age: 35
Posts: 3,833
FPOBN, wake encounters are reported on by pilots. If there is a breach in WT separation, then the controller will also file a mandatory report.

No conspiracies here.

Last edited by Gonzo; 21st Dec 2012 at 08:13.
Gonzo is offline   Reply
Old 21st Dec 2012, 09:13   #30 (permalink)
 
Join Date: Nov 2011
Location: In the middle
Posts: 41
Maybe I am wrong (I am always open to debate) but...

I went through the documents;

http://www.faa.gov/other_visit/aviat.../SAFO12007.pdf

and

https://fdx.alpa.org/LinkClick.aspx?...%3D&tabid=4536

Regarding the FAA rules, you are right, Table 1 is showing the wake standards at the Threshold.

But I'm not sure about the statement:
Quote:
IF the runway has a 2.5nm MRS, then the min wake is 2.5nm, IF the runway has a 3nm MRS, then the min wake is 3nm. I just went through this at KMEM and FedEx.
I mean, if the airport is not allowed to use 2.5nm spacing, it does not mean that the wake turbulence separation (minima) changes... As far as I understand, the 2.5nm is always the very minimum wake (FAA), but to be "unambiguous" regarding the minimum separation in sequence for different airports, the MRS is stated. (And MRS is never below 2.5nm, so never less than minimum wake sep.)

You can also go through;
http://www.wakenet.eu/fileadmin/user...T_FAA_Lang.pdf
and you will find some blank cells in ICAO tables...

Anyway, the first impression when reading the presentations is, that wake sep. are still "overly conservative".
UpperATC is offline   Reply
Old 21st Dec 2012, 10:18   #31 (permalink)
 
Join Date: Oct 2007
Location: MANCHESTER
Posts: 19
I think the point made above about the 4nm cut off is critical. The wake separation applied in the UK only applies until the first aircraft is at 4nm. The first aircraft then reduces to threshold speed so some distance compression will occur; however as the second aircraft will also reduce speed from 4nm to the threshold the time separation between the two flights will remain constant or at least very similar.

AFAIK this arguement has always been accepted by the CAA.

If you applied vortex spacing to the threshold at Heathrow from today the movement rate would fall off a cliff.

Wake vortex reports are taken very seriously by both NATS and the CAA and I have never known anyone attempt to cover any up.
seahawks is offline   Reply
Old 21st Dec 2012, 16:04   #32 (permalink)
 
Join Date: Mar 2011
Location: engineer at large
Posts: 1,414
del prado,
The reason for citing FAA RECAT is that ICAO asked EUROCONTROL and the FAA to re-categorise aircraft and develop new wake turbulence separation standards.

What you are seeing is the EUROCONTROL/FAA RECAT Phase 1 program. IF this is adopted by ICAO, this will be coming to an airport near you.

UpperATC,

Under RECAT 1, there is one separation standard. There is not a different minimum sep per visual/radar conditions.
The only difference in the standard, is as illustrated in the table..IF the runway has the 2.5nm MRS sep, the min RECAT is 2.5...IF they have the standard 3nm MRS, then the min sep is 3nm...



From the FedEx document you reference, the runways they use do not currently have the 2.5nm waiver, so the min wake sep of 3nm is illustrated...

(note 777 to 777)






As you have noted, the RECAT standard for sep is threshold to 10nm. This was moved out from threshold to 5nm (typical FAF) to harmonize with TRACON.

Last edited by FlightPathOBN; 21st Dec 2012 at 16:06.
FlightPathOBN is offline   Reply
Old 21st Dec 2012, 16:35   #33 (permalink)
 
Join Date: Jun 2009
Location: behind the fruit
Posts: 198
*other freight carriers are also available
LEGAL TENDER is offline   Reply
Old 21st Dec 2012, 18:17   #34 (permalink)
 
Join Date: Nov 2001
Location: Around
Posts: 283
I must say, it takes big stones to lecture a Heathrow controller (Gonzo) on final approach spacing, especially for someone who isn't a controller. Chapeau.
rodan is offline   Reply
Old 21st Dec 2012, 18:44   #35 (permalink)
 
Join Date: Mar 2011
Location: engineer at large
Posts: 1,414


Application of Wake Turbulence Separation at London Heathrow

adding this on reporting wake...as it is as clear as mud...

6 Wake Turbulence Encounter Reporting and Research

6.1 Wake Turbulence Encounter report forms are available to download from the CAA website as follows:
(a) Pilot Report Form: SRG1423: Wake Turbulence Report Form | Publications | About the CAA
(b) ATCO Report Form: http://www.caa.co.uk/srg1422

Full instructions for submission of the report forms are contained on the forms.

6.2 Pilots of aircraft believed to have created the wake turbulence will be informed by ATC and are requested to complete the appropriate sections of form SRG1423. The sections are identified on the form. (emphasis added)

http://www.skybrary.aero/bookshelf/books/1166.pdf

Last edited by FlightPathOBN; 21st Dec 2012 at 20:31.
FlightPathOBN is offline   Reply
Old 21st Dec 2012, 21:26   #36 (permalink)
 
Join Date: Jan 2004
Location: London
Posts: 407
FPOBN, UK already has a difference to ICAO as I described above (wake separation to 4 dme not threshold). That's why I don't see the relevance of the info you've posted. If ICAO adopts RECAT I cannot see UK adopting it. The drop in movement rate at heathrow would be too great.
Do you believe the UK CAA would risk heathrow by adopting it when the present system has worked for many years?

Your quote under 6.2 in your last post was what I was getting at earlier when I said both flight crews are requested to file (sorry if that wasn't clear).

Work is ongoing to develop time based separation at heathrow, where the time interval between arrivals will be constant but the gap will vary according to the head/tail wind. How does that fit with RECAT?
Del Prado is offline   Reply
Old 21st Dec 2012, 21:35   #37 (permalink)
 
Join Date: Oct 2000
Location: Berkshire, UK
Age: 69
Posts: 7,180
<<6.2 Pilots of aircraft believed to have created the wake turbulence will be informed by ATC and are requested to complete the appropriate sections of form SRG1423. The sections are identified on the form. (emphasis added)>>

That's been the case for m any, many years. It means that if a pilot reports wake turbulence then the pilot of the aircraft causing it is asked to complete a form. I must have done it hundreds of times.
HEATHROW DIRECTOR is offline   Reply
Old 22nd Dec 2012, 00:06   #38 (permalink)
 
Join Date: Mar 2011
Location: engineer at large
Posts: 1,414
del prado,

The post, was directly from the document by Paul Johnston, Application of wake turbulence at London Heathrow, read the document link...

https://docs.google.com/viewer?url=h...ul_Johnson.pdf

Quote:
UK already has a difference to ICAO as I described above (wake separation to 4 dme not threshold)
that is not what is stated in the document...

I placed the red box over the text....

.. applied to 4DME FROM touchdown
FlightPathOBN is offline   Reply
Old 22nd Dec 2012, 06:49   #39 (permalink)
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 2,999
Quote:
that is not what is stated in the document...

I placed the red box over the text....

.. applied to 4DME FROM touchdown
Are you making a distinction here between "touchdown" and "threshold" ? Or is your highlighting of FROM intended to mean something else ?
DaveReidUK is offline   Reply
Old 22nd Dec 2012, 13:11   #40 (permalink)

 
Join Date: Dec 1999
Location: LHR/EGLL
Age: 35
Posts: 3,833
FPOBN,

Yes, it is applied all the way down the approach UNTIL the point where you are 4nm (4DME) FROM touchdown.

It is not applied from the point to touchdown. The "from" in this context does not denote the starting point of the separation, merely the way of measuring the end point.

As you well know, nothing is certain when we talk about ICAO/harmonisation of ATC procedures. FAA have introduced RECAT1A (A for America!). Europe may introduce RECAT1E (E for Europe) which is subtly different.

However, I still don't understand the point you're trying to make.

Applying wake turbulence spacing to 4DME is a well-understood procedure in the UK on the part of the controllers and the regulator.

I am not aware of any safety issues.
Gonzo is offline   Reply
Reply
 
 
 


Thread Tools


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 03:09.


vBulletin® v3.8.7, Copyright ©2000-2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
1996-2012 The Professional Pilots Rumour Network