Time based final approach spacing

[HEATHROW DIRECTOR]

I gather that time based separation is to be trialled at Heathrow soon. I'm curious to know how it will be achieved by ATC. Distance spacing is straightforward using radar but using time I don't understand. Anyone care to fill me in with the basics please? Thanks.

[Dan Dare]

The glossy brochure video from NATS is here (http://www.nats.aero/newsbrief/time-based-separation-heathrow-world-first/)

The bit that you really want to see is about 2:40 in, but the rest of the video may be of interest. It is actually really good stuff!

[HEATHROW DIRECTOR]

Many thanks Dan... will mug up on it.

[Talkdownman]

One day, HD, Number Two Director will simply say 'lock on to the one in front and fly 90 seconds behind it…'…and HAL will rub its hands at getting a consistent 40/hour…whilst Air Arrivals occasionally glances over the top of his newspaper...

[2 sheds]

...on half the salary!

[HEATHROW DIRECTOR]

Yeah - very glad I'm out of it!!

[DaveReidUK]

Should make for some great photo opportunities on windy days.

[ZOOKER]

Talkdownman,
Love it, especially when Air Arrivals spots 3 going-around, as opposed to just the front one with the problem.

[davys747]

I am only a lowly Area controller so forgive my ignorance.

Are they really trying to say, in an overly complex and fancy way: We will use time based wake turbulence separations and then convert those into distances for a given wind, in the cases where the time separation (as a distance) would be less than the current published distance requirement?

E.g. H v H (Requirements: 4nm or 2 minutes)

No wind: GS ~160kts : 2mins = 5.33nm so distance based (4nm) is more efficient;
40kt headwind: GS ~120kts : 2mins = 4nm so either or;
60kt headwind: GS ~100kts : 2mins = 3.33nm so time based more efficient.

[Jungmeister]

This is circulating in OZ http://http://www.bbc.com/news/magazine-31109732 (http://www.bbc.com/news/magazine-31109732)

[Gonzo]

Davys747,

Yes, but in all cases we use the distance equivalent of the time achieved by using distance criteria in a headwind of 5-7kts.

So when the headwind is less than this, or a tail wind exists, the aircraft will be further apart than they are now. This is precisely the circumstance which generates the vast majority of wake encounters/reports today; calm conditions.

[118.70]

I see AIP says :

"(c) During TBS operations, RNAV (GNSS) final approach requests may be refused by Heathrow Director to ensure runway
efficiency is maintained."

Is this because RNAV doesn't have the speed flexibility to cope with TBS ?

[bekolblockage]

I think we've discussed this before Gonzo but I'm still not convinced.

The initial impression it gives to the industry is that it is a clever way of closing up the traffic distance-wise without suffering the erosion in W/T separation because the time remains the same.

That is clearly not the case.

Using the analogy in one of the articles, of trying to walk down an upwards moving escalator, the parcel of air the wake is generated in, is akin to one of the escalator stairs. It makes no difference the escalator/wind speed, the following aircraft will arrive at that parcel of air at the same time for a given spacing.
If you shorten it, you will hit it earlier.

Now, someone in NATS has realized that this "relativity" oversight was not going to pass scrutiny so has had to assume that the wake will always be dissipated quicker in a stronger wind. That would depend on the wind gradient and terrain which would cause mixing one would assume. Its not a given that the wake will disspate quicker. Indeed, the wake does not even "know" there is such thing as wind. Its just generated in a parcel of air that may or may not be moving.

I will be interested to see if you have a significant increase in W/T occurrences.

[Crazy Voyager]

I don't think you can say anyone has "assumed" the W/T will dissipate quicker, they have done years of measuring at Heathrow to prove that it does disippate quicker in stronger winds.

This isn't something that's been made up, there is a lot of hard work and data research behind it. The article mentions four years of work and data gathering from 150 000 flights.


I agree though, it will be interesting to see if it has an effect on the amount of WT encounters, and if that is an increase or decrease (as in some winds spacing will now be increased from before, as Gonzo mentioned above).

[kcockayne]

bekolblockage

I'm totally in agreement with you. This whole strategy appears, to me, to have been "reverse engineered". ie You start with the result you desire & then arrange the "evidence" to fit in with the desired result.
Much the same as the Tower doing Radar !
As ever, time will tell .....& I could be wrong !

[Gonzo]

Well, there's not much I can say, you seem to have made up your minds.

I know I've been working on TBS and other wake concepts for over seven years, but within SESAR and NATS it has been worked on for over ten, so maybe you were involved in the early days? Or attend the few meetings I fail to make due to other commitments?:)

[zkdli]

nice one gonzo!

[kcockayne]

Nothing personal, Gonzo. I don't think that I even know you. But, from the outside, it often seems that changes to ATC are being introduced without regard to previously "sacrosanct" procedures & requirements. And, when you look closely at those changes eg ADC Radar, "Tunnels in the sky" etc nothing has actually changed to enable you to throw out the old system with, what I would call, any real conclusive supporting evidence.
I'm perfectly willing to accept that, from your viewpoint (& I accept your personal involvement in this subject as being highly relevant), I may be "talking through my arse". I do not intend to denigrate your work !
But, from my viewpoint, a lot of these changes appear to be based on wishful thinking & a total reliance on technology to get you through.
I suppose that it's always painful to have to ditch familiar old , tried & trusted techniques, but I have reservations about this one; BUT, I acknowledge that you are far more familiar with the topic than I am.
Good luck with it.

[Crazy Voyager]

The combination of aerodrome control and radar has been done for years (probably over a decade) outside of the UK. If it works there, why not in the UK?

Not directly related to TBS, but I think if the safety case has been proven in practice for years outside the UK and approved byt he CAA, then it can be considered to be acceptable.

So you have one concept which was proven before it was brought in the UK, still there are many doubting wether it will work.

Then you have a concept (TBS) which has been designed from scratch, within the UK, and still the same doubts arise?

To very different developments met with the same response, what did they both do wrong in order to get that response?

[Glamdring]

As far as ADC & Radar goes, the safety case may be sound but there is a lot of double standards imho. For instance, we can't use the additional uses of the ATM when bandboxed....but we can vector traffic on it? :}

[Gonzo]

Fair play kcockayne.

I guess I just feel slightly piqued when those who admit they are not familar with the project say that the changes are being introduced without evidence/safety assurance etc.

I'm not getting at you personally here, BTW. TBS is coming to all major airports, by 2024 at the latest, I think; according to EC Implementing Regulation 716/2014:

Time-Based Separation for Final Approach shall be operated at the following airports:
—
London-Heathrow
—
London-Gatwick
—
Paris-Orly
—
Milan-Malpensa
—
Frankfurt International
—
Madrid-Barajas
—
Amsterdam-Schiphol
—
Munich Franz Josef Strauss
—
Rome-Fiumicino
—
Zurich Kloten (5) (http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32014R0716#ntr5-L_2014190EN.01002401-E0005)
—
Düsseldorf International
—
Oslo Gardermoen (6) (http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32014R0716#ntr6-L_2014190EN.01002401-E0006)
—
Manchester Ringway
—
Copenhagen Kastrup
—
Vienna Schwechat
—
Dublin
I'd far rather provide wake turbulence separation that is based on science and fact than on a 'finger in the air', one size fits all approach that takes no account of atmospheric conditions and wake behaviour. The 'tried and trusted' wake separation rules applied in tailwind conditions result in a significant increase in wake encounters as decay rate is low. The data shows that we need need to increase separation in tailwind conditions. The data also shows, and I am more than willing to be corrected on this, that there hasn't been a wake encounter on approach at LL when the surface wind has been above 10kts (or is it 15kts? Not sure).

As for a total reliance on technology, I think ATC is well past that point! Did we have the same arguments when radar was first introduced for civil ATC?

[kcockayne]

Safety Cases & Risk Assessments reared their ugly head during the latter years of me being an ATCO. I well remember being asked to carry them out (the whole unit never having done one before). We asked the SRG for guidance on what had to be done & how to do it. Their response ? None ! (other than that we'd have to find out for ourselves -which we did with the help of EGSS SATCO/Chief Officer).
Prior to that, ATC adopted a "Fail Safe" Approach.ie if the Radar failed, & separation was likely to be compromised, then it would have to "fail safe". This was built into separation standards etc. & applied to the whole range of ATC procedures in this, & other areas.
Safety Cases & Risk Assessment don't quite fill me with the same sense of confidence in the system, somehow. It's not so much that they don't Guarantee a safe system subsequent to the failure; but, that they seem to assume that there WILL BE NO failure !
It's not just ATC. Just look at ETOPS operations. I accept that there have been no disasters (for which I am exceedingly thankful ; although there was a very near miss in the Azores with the TSC EA33; but, how can Risk Assessment & Safety Cases guarantee that there never will be ?
And IF there ever are any, no amount of Safety Cases & Risk Assessment exercises are going to avoid them !

[kcockayne]

Gonzo

Just seen your latest. Thank you for your comments. I take your point about science & technology & would, in NO WAY, seek to accuse you of not going about these subjects without due diligence or without satisfying yourself as to their efficacy.
Reading my post, above, I guess that it becomes pretty obvious that we come from two very different ATC cultures. Mine being one where the ATCO was in "total control" & yours being one where you are prepared to totally trust in technology.
As I have said before in these pages, I am glad that I am now out of it....and, you probably are , too !
Nevertheless, I genuinely wish you well with it all. Maybe, one day I'll come back & visit & be totally impressed with it all. Or, maybe I'll still pick holes !

[Gonzo]

kcockayne,

& yours being one where you are prepared to totally trust in technology.

Well now, lets not be rash! :}

I think we have more in common than you believe. Given the opportunity to do GMC from the old tower at Heathrow, with paper strips, and no A-SMGCS I'd bite your hand off, especially if it was bandboxed and really busy. That was FUN!

A simpler time.

Technology, and the demands of the industry, have moved on. I think we have just about reached the limit of ATCOs being in 'total control' in terms of capacity, and to keep on that upward curve, tool support is the only way forwards. An ATCO remembering the 6 UK wake categories and the separations is feasbile, but Static-Pair Wise separation, with a 96x96 matrix of individual aircraft pair separations to the nearest 0.1nm is beyond anyone's comptence.

I have raised, and still raise, issues with new projects, equipment and procedures. That's why I started getting involved in them.

[vector4fun]

Interesting, we did timed approaches in non-radar environments back in the '70s, then went to radar separation, then were told that ADSB accuracy was going to improve all that, then I read here that GB is going back to "Timed approaches" again. What's old is new again.


V4F, (3 wonderful years retired now) :ok:

[tired]

Think this has started already? How's it going?

[DaveReidUK]

Starts on 24th March, according to a NATS presentation I'm looking at.

[118.70]

Forecast looks a bit blowy for the weekend.

Time to give TBS a whirl ?

[coldfy]

It has started now

[DaveReidUK]

Forecast looks a bit blowy for the weekend.

Time to give TBS a whirl ?

Very droll. :O

[Cough]

Flew down final at the standard 5nm behind a heavy (Cough in a medium) today despite 40kt headwind on final. Cleared to land at the normal point, with a normal slot delay on departure from the outstation.

Has TBS seriously started, or are you slowly easing into it?

[DaveReidUK]

Has TBS seriously started, or are you slowly easing into it?

A cynic might suggest that it will only operate Monday-Friday, 9-5. :O

[HEATHROW DIRECTOR]

One CAA boss actually thought that ATC only worked from 9-5!

[kcockayne]

Obviously eminently qualified to be a boss !

[Gonzo]

Cough, yes, to both questions!


Bear in mind that it was only switched to Time mode on the 24th, so many ATCOs have not yet used it in such a mode outside of the simulator. Also, we are still in the phased introduction, so it may be that for a period around your arrival it was in distance mode anyway.


I've seen many wake pairs today separated by significantly less than that required under the distance separation criteria.

[Cough]

Gonzo - Cracking to hear, we were both expecting to be quite a bit closer at the time, but a slow phase to this mode of operation without surprises is essential:ok:

Now, can we start on the CAA on moving the min radar sep for a medium to 2nm (only used in the TBS regime!).... Packing in us mediums would really help!

[HEATHROW DIRECTOR]

As long as you get off the runway quickly!

[Gonzo]

Cough,


2nm minimum radar separation is being worked on within SESAR.

[EastofKoksy]

"2nm minimum radar separation is being worked on within SESAR"

I think Cough might like to benefit from this before he is due to retire!!

[Cough]

HD - Was getting off the runway in time ever a problem in 40kt headwinds? 15kt TW to 100' always makes things exceedingly tight, though minimal holding!

Gonzo - Thanks for that - Will be a long time off then!

EastOfK - All I'll say is by the time that it does come along, I probably won't be concerned with medium wake vortex!

[ZOOKER]

"2nm radar separation is being worked on within SESAR'
Interesting statement.
I was taught that en-route and approach radar radar separation minima were different due to the technical limitations of the equipment employed in those functions.
Area radar....50cm, or 23 cm radars, refreshing at 10rpm, required a separation 'minima' of 5nm. (10nm in azimuth outside of certain ranges from the radar source).
Approach radar....10cm equipment refreshing at about 15rpm, gave a separation 'minima' of 3nm.
What new equipment are SESAR mandating/installing which will allow this proposed reduction in radar separation minima, and therefore safety?

[eglnyt]

Multi-Static Primary Surveillance Radar, previously discussed on this forum, and Multi Lateration of the Mode S signal both have the potential to reduce separation standards primarily because they remove the restriction of a refresh rate based on how fast you can turn a heavy lump of metal.

[Gonzo]

2nm MRS should be getting to V2 maturity in SEASR, not sure of the progress as I'm not directly involved. V2 is the feasbility stage, so effectively to develop a mature concept only.

I know that the project had identified technical and operational issues, among which, I assume, is the currency (update rate) of the surveillance picture. I assume also that the solution to this is muti-static and/or multi-lat. There's a lot of RF energy out there reflecting off aircraft.

edit: cross posted with eglnyt

[ZOOKER]

There's a lot of RF energy out there, reflecting off all kinds of things.

[118.70]

Hundreds of flight delays hit Heathrow (http://www.travelmole.com/news_feature.php?news_id=2016067)

Hundreds of flight delays hit Heathrow



Hundreds of flights were delayed at Heathrow two days after a new system went live to 'cut delays caused by strong winds'.


The delays affected 287 flights taking off from Heathrow on Sunday and 288 flights arriving at the London airport, according the flight data website Flight Aware.


The new system, Time Based Separation (TBS), went live on Friday and was described as a 'world first'.


In a press release by NATS, it said: "A new way of separating arriving aircraft at Heathrow Airport by time instead of distance in order to cut delays caused by strong winds has gone live as part of a phased introduction this year.


"Traditionally, air traffic controllers separate flights by set distances dependent on the aircraft type and the size of the spiralling air turbulence - or wake vortex - they create as they fly.


"Time Based Separation (TBS) takes live wind data from the aircraft to dynamically calculate the optimal safe spacing between each aircraft in order to maintain the landing rate. Its introduction is expected to halve current headwind delays at the airport and significantly reduce the need for airlines to cancel flights."


A spokesman for Heathrow Airport said: "There were delays at Heathrow yesterday due to very high winds.


"We had no cancellations (out of the approximately 1300 scheduled flights) so although we are running at 98% capacity the airport coped well with the weather disruption.


"Of course we are sorry for those passengers who were delayed yesterday."


A spokesman for NATS said: "The tool is obviously new so it will take some time for us to be getting the absolute most out of it.


"We are currently in a period of Limited Operational Service to refine our processes and ensure everything is working as expected. We then plan to go fully live on 1 May, although further refinements will probably be made over the course of the year."

Monday, March 30, 2015

[HEATHROW DIRECTOR]

Oh dear........

[Jwscud]

So how is it working at the coal face? Windy as it has been for a while now.

[Gonzo]

There no 'oh dear' about it. It's in limited operational service.

Perhaps we should wait until after O date before we all pile on, eh?

[Minesthechevy]

Nah, where's the fun in that Gonzo? It's much easier to get stuck in early.... After all, when we were all learning to drive, NONE of us EVER stalled the Model-T, not once, ever. Did we, boys?

[DaveReidUK]

Interesting presentation this morning from NATS and Lockheed Martin. No real surprises, but some useful background on the trial and the experiences since it started on the 24th (at 15:05, to be precise, with the first aircraft handled being BAW14GM, an A319 from Linate).

The weekend, needless to say, saw the benefits start to kick in with the high winds, with separation distances being reduced in some cases by over 30%, eg a 5nm pair being spaced at 3.4nm in the 50-60kt winds and around a 6-7 landings per hour improvement compared to distance-based separation in the same conditions.

A recording of the presentation can be downloaded from here: Time Based Separation (http://more.civil.external.lmco.com/intelligent-approach) (registration required).

[DaveReidUK]

Also now up on YouTube, for anyone who prefers to watch anonymously: https://www.youtube.com/watch?v=SD7zia4eF5o

[good egg]

Very informative....when will flow rates for strong winds be lifted I wonder? Evidence so far seems to suggest it should be soon :)

I'm also very interested in when it could be applied to a single runway (mixed mode) operation. I can see that both distance-based-markers and time-based-markers (in the fullness of time!) would be of use to both the airport where I work and the approach unit. (In our case WTS is not such an issue in peak times as the mixed mode spacing is seldom less than WTS, however, it would provide a useful tool for consistency of spacing for approach control.)

[I_Like_Blips]

Here's some NATS publicity about a first look at Time-Based Gaps for a single runway airport.

Building a shared picture for Tower and Approach | NATS Blog (http://nats.aero/blog/2014/10/building-shared-picture-tower-approach/)

[HEATHROW DIRECTOR]

<<Getting the most from a single runway needs great cooperation between the controllers in the tower and those working in approach to interweave arrivals and departures.>>

I think I have just come up with a winning idea... Why not have the approach and radar units at the airfields so that the controllers could have validations for TWR and APC? Wouldn't this give everyone a better understanding of the other side of the job? Expect somebody has already thought of that...

[Dan Dare]

Yep HD they're already a step ahead of you:-


Radar in tower (one controller)
Remote tower ops
CPDLC replacing radio


Expect to see all of Heathrow done by one person in an industrial estate in Romania soon :eek:

[HEATHROW DIRECTOR]

I love it! A bloke from one of the universities came to Heathrow donkey's years ago and said he was looking into automating the set-up, apparently at the behest of CAA. I told him he'd be better employed finding a better way to sort out the EG list. Didn't go down too well with some be-suited people!

[ZOOKER]

HD and Dan,
brilliant.
This has moved on a bit since I last looked.
Also, why not put the area control centres near to the airports too?...Then, airport and en-route staff could visit each other's places of work to see what happens. It might create a spirit of 'team-building'. Also, 'Pilots'.......Who are the 'End-users'.....Er, sorry....'Customers', of the services provided, could easily visit all sides of ATC to see what's going on?

[Eric T Cartman]

Even better Dan, maybe they'll find an industrial estate in West Drayton ;-)