Time based final approach spacing
 

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.

The glossy brochure video from NATS is here

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!

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

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...

...on half the salary!

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

Should make for some great photo opportunities on windy days.

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

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.

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

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.

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 ?

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.

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).

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 !

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?:)

nice one gonzo!

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.

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?

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? :}