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Old 22nd Dec 2012, 15:49   #41 (permalink)
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It is impossible to apply separation inside 4d anyway. Since we are unable to apply speed control past 4d, there's no method of doing so other than adding half a mile and hoping for the best, which doesn't seem like much of a safety case.

The point about wake turbulence is that it dissipates over time, not distance. The distances we apply are approximations that roughly correspond to the time taken for the wake to dissipate sufficiently at normal approach speeds. Since both aircraft in a pair will slow down after passing 4d, the time gap is maintained even if the distance isn't, so it really isn't an issue.
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Old 22nd Dec 2012, 16:48   #42 (permalink)
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it is called minimum separation distance, correct?

As far as safety, that is relative. LHR does appear to have quite the distinction on wake encounters.
In 2010, 65% of the reported wake encounters reported were at LHR. of the 210 encounters at Heathrow, 74 were below 500 feet, with another group of 100 at 4500 feet (where the turns come on to final)
Of the 74 below 500, 32 were listed as severe.

And from 2007

Highlights from the 2007 NATS Wake Vortex Analysis Report were:
- Prime aim was to monitor spacing effectiveness and identify follow-up actions to address.
- The value of the report relies on accuracy and capture of all relevant facts.
- 227 reports in UK airspace in 2007 of which 54 were severe 197 reports in 2006. The majority were inbound/outbounds at Heathrow. A trial has just commenced at Heathrow using LIDAR to investigate further.

LHR 2015

Landings at San Diego Int Airport Nov 23, 2012 - YouTube

Last edited by FlightPathOBN; 22nd Dec 2012 at 16:57.
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Old 22nd Dec 2012, 17:46   #43 (permalink)
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How surprising that the majority of the UK's wake turbulence encounters happen at the world's busiest two-runway airport.
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Old 22nd Dec 2012, 17:47   #44 (permalink)
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Heathrow had about 30% of the traffic in the UK in 2011. Given that they apply minimum wake turbulence spacing between a far, far higher proportion of their traffic than any other UK airport, nowhere else even comes close, 65% sounds doesn't sound excessive at all to me.

I don't have the figures, but I wouldn't be remotely surprised if, per traffic pair at minimum spacing, they actually had a better safety record than anywhere else since they practice it so much.
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Old 22nd Dec 2012, 18:12   #45 (permalink)

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I'm still struggling to take on board your point. Either that or you seem to have many and I'm confused by them all.

The original question was about LHR arrival separations, and you then talk about what the FAA apply in the USA.

You have now highlighted the fact LHR seems to have the most wake encounter reports..that may be related to the fact that LHR has more pairs at wake turbulence separation distances than any other airport in the UK, and you have included departure reports, when we are discussing arrivals.

Also, I would point out that a wake encounter itself is not in and of itself a safety incident.

Nor is wake turbulence separation intended to negate vortex encounters, it is merely intended to reduce the frequency of severe wake encounter to an acceptably low level of risk.

You mention the phrase 'minimum separation distance' which I've never seen as a defined phrase in nearly fourteen years in ATC.

Your last post is a piece of art which represents all the landings in one day at San Diego, under the title of 'LHR 2015'

What is the main point you're trying to get across?
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Old 22nd Dec 2012, 18:26   #46 (permalink)
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Sounds like a very good reporting system is in place at Heathrow and there must be a tremendous amount of data available to prove a safety case to ICAO.

Funnily enough in the wind conditions today, easterlies with a tailwind required an extra mile on the spacing (and wake separation) while westerlies into a strong headwind was minimum radar and wake separation.

FPOBN, the time interval between inbounds was shorter when we added an extra mile in a tailwind and longer when providing minimum separation in a headwind. So which was safer, the longer distance or the longer time interval?
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Old 22nd Dec 2012, 18:39   #47 (permalink)
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To put that number in 210 for LHR in context, for the same year,
there were 50 reported wake encounters for all of the airports in the United States.

Sounds like a very good reporting system is in place at Heathrow and there must be a tremendous amount of data available to prove a safety case to ICAO.
Yes, and RECAT is the result.
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Old 22nd Dec 2012, 19:02   #48 (permalink)
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<<there were 50 reported wake encounters for all of the airports in the United States.>>

Given the astronomical number of aircraft movements in the USA I find that extremely difficult to believe.

Wake turbulence can be encountered when there is more than minimum WT separation. I had an aircraft go out of control when it was over 10 miles behind a heavier aircraft.
Old 22nd Dec 2012, 19:10   #49 (permalink)

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One could argue that the UK had already done 'RECAT', with its designation of:

Just swap the words 'Upper Medium' for 'Lower Heavy', or Cat C in RECAT1A parlance.

Rather than ICAO...


Also, your chart of the FedEx 777 wake turbulence separations.....

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)

Under RECAT1A, 777v777 is 3nm for wake separation. It is not dependent on radar separation rules as you say. Even if they did operate into a US runway where the separation could be 2.5nm (I'll take your word for it that they don't) then it would still be 3nm 777v777.
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Old 22nd Dec 2012, 20:34   #50 (permalink)
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1. In FAA region, 2.5nm is the min possible separation all the way down to the threshold. (we understand that)
2. In FAA region, 2.5nm is also the min wake turbulence separation for certain acft pairs.
3. In FAA region, (and not just there) MRS is not the same as WTS, and you will have to accept this. The numbers (nm) can be "equal" in certain situations, but it is just not the same... MRS "depends" on the aerodrome, while WTS is always there, prescribed, in force... (as a Controller, you apply MRS or WTS, whichever is higher)

And now...
4. The FAA region is not the only region on the Earth... So you will have to accept that in the UK the 2.5nm is not the only possible min separation down to the threshold. Guys here tried to explain the 4DME principle... But you started with occurrence reports...
I will again add an old document: see the difference

5. Your (FedEx) picture about 777 leader and follower... This is a B-B (category) situation. Never below 3nm.
But when a FedEx MD11 will be in front of the FedEx 777, the separation could be 2.5nm (Virtual Memphis with waiver ) or 3nm (presently Memphis - your words about no waiver). Do you think that wake vortices change with the waiver?

Finally, I do not understand where you want to drive the debate? If you want to show us all that the min separation standards are not OK, well in this case I think this is just not the right place... You can easily write a good letter to the appropriate authorities and explain your doubts. You can also attach all the statistics you posted here.
However, if you went through all the links, your eye should saw a statement (from FAA, EUROCONTROL) that; "Current ICAO, US and European separation standards are different, but all are safe. In the US or Europe there has never been an accident caused by wake vortex under IFR separations and procedures." Not my words... Today's link has also some reports.

I hope it will help.


Last edited by UpperATC; 22nd Dec 2012 at 21:16.
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