time based separation
 

Hi ATCers

Just reading an article in the March 2014 edition of E&T (Engineering and Technology publication) about the introduction of time based separation on approach to LHR rather than distance based separation which is expected to halve delays (their words not mine) and I'd be interested in your thoughts please

regards (and be gentle)

Halving delays sounds very optimistic. Are you asking why it would reduce delays or about the halving?

Is this for mixed mode ops?

Have a look at the NATS website, there is more about TBS and a short video there.

The one sentence version is that we're taking the time achieved by distance based wake turbulence separation in low headwinds conditions (for example 4nm=90s) and then taking that time and applying it across all headwind conditions, so that in strong headwinds separation between Heavy/Heavy might actually be 3.7nm.

The result is that the landing rate is maintained is strong headwinds.

As Zooker says, lots on the NATS | A global leader in air traffic control and airport performance website.

Chevvron, for LHR it's obviously aimed at a dedicated landing runway, but it's also being developed to ensure it can be used at busy single runway airports, where you can compress the 'departure gap' in headwinds.

What have they been doing for the last 40 years at Gatwick* then?



*other busy single runway airports are available.

Waiting for TBS, like everyone else. :O

thanks
 

Zooker, Gonzo thanks for the useful explanation (and I will follow the link to watch the vid, just can't from this machine).

Actually, we've been using time based separation at Gatwick (and presumably many other airports) for at least 20 years, it's just that we express it as a distance because that's what the approach guys and girls see on a radar screen. Hence departure gaps vary between 7nm (slight tailwind), 6nm (calm), 5nm (reasonable headwind), or even 4nm (stonking headwind) with .5nm variations to tweak the gap to achieve the same time between landers...so time based separation is actually nothing new though I'm sure an expert somewhere will claim to have invented this magnificent innovation though....:ugh:

I thought the whole point of TBS was to allow a reduction in the physical spacing of arriving aircraft in strong headwind conditions, to mitigate at least partly the effect of said headwind on the arrival rate? Obviously mainly relevant to segregated operations.

Maybe it will come in handy at Gatwick when you get your new runway. :O

This "expert's" pat on the back will come from convincing the CAA to let us go below the current wake turbulence seperation minima! That's the main difference between what you've been doing at Gatwick all this time and what Heathrow might soon be allowed to do.

I just wonder how radar controllers will apply TBS? All I've seen are lines moving down the centreline, which presumably indicate times, which I assume controllers have to aim aircraft at.

Wait around long enough.....

That been said Time Based Separation as now envisaged is part of the SES and SESAR.

Aircraft will be given a time to cross a given point +/- a parameter.

Long term it is believed to be part of the solution to some of Europe's capacity issues.
Once all aircraft are suitably equipped :rolleyes:.
The roll out of ADS-B above FL285 is another part of the grand plan.

Biggest difficulty for ATCO's will be during mixed mode operations.

Jeez, calm down.

The TBS concept effectively compresses the wake turbulence separation.

However, the spacing/separation tool is accurate down to 0.1nm so will allow Gatwick, or Heathrow, or any other airport if they deployed it, to more accurately refine the departure gaps in single runway ops. We all change the gaps in SRO according to the headwind and runway occupancy, but as you say vespasia to 0.5nm, not to 0.1nm increments.

What additional equipment is required on board aircraft to allow ATC to move to time-based separation?

Just curious.

DR,

I think confused ATCO is talking about aircraft being equipped to fly 4D trajectories with required time of arrival, not TBS final approach separation/spacing.

Anyway, if any NATS people want more info, PM me, for others, I know the NATS Press Office has a lot of material on TBS.

Gonzo
 

Interesting, and on the face of it, reasonable solution to the problem. With our 65:35 Heavy:Medium traffic mix, we lose about 1 arrival per hour for every 5 kt h/w increase over 10 kts.

But is the logic flawed?

Certainly on strong headwind days, the aircraft are passing over a point on the ground at longer time intervals.
But the aircraft and the wake vortex they produce are both moving relative to the mass of moving air. Surely the wake vortex generated is not staying stationary over a point on the ground? If that was the case then yes, this proposal would be reasonable.
But to the following aircraft, won't the wake still be reached in the same time, for a given spacing, regardless of the wind?
In simple terms, the airborne aircraft and the vortices don't "know" there is such a thing as wind.
Sounds like you have the Regulator convinced anyway. :ok:

I was wondering whether the separation could be closer with a steady crosswind, because the vortex would be blown to the side and so the following aircraft wouldn't intersect it if they were all crabbing/slipping down the runway centreline.

Does the headwind version work because the following aircraft goes over the top of the vortex from the preceding aircraft?

Bekolblockage,

Wake degrades at a faster rate the higher the wind speed. There was a LIDAR research campaign as part of SESAR


llondel,

There is a partner to TBS in terms of concept, called CROPS, or Crosswind Operations, which works on that very idea. Both departures and arrivals can benefit from the effect you describe.

I'd have thought that the distance between the preceding aircraft and the wake vortex it generates would be a constant, regardless of headwind strength.

You seem to agree:

In that case, for a given spacing, the following aircraft would take longer to reach the preceding aircraft's vortex in a stronger headwind.