time based separation
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I think you need to study the trajectory of the wake vortexes; They tend to drop 100ft quite quickly, then level off and not change their height thereafter.
So if anything, a headwind would blow the turbulence horizontally nearer the following aircraft, during the initial drop.
The 'straight' part of the vortex trail will however be parallel to the 3deg glide slope, and will be blown backwards away from the actual glideslope by the headwind.
However because of the low angle of the glideslope (where tan 3 only = 0.05), the amount that the turbulence moves away for a 90 second spacing and a 10kt headwind is only 78ft.... maybe better than nothing though.
So if anything, a headwind would blow the turbulence horizontally nearer the following aircraft, during the initial drop.
The 'straight' part of the vortex trail will however be parallel to the 3deg glide slope, and will be blown backwards away from the actual glideslope by the headwind.
However because of the low angle of the glideslope (where tan 3 only = 0.05), the amount that the turbulence moves away for a 90 second spacing and a 10kt headwind is only 78ft.... maybe better than nothing though.
So if anything, a headwind would blow the turbulence horizontally nearer the following aircraft, during the initial drop.
If the headwind is blowing the vortex-containing air across the ground at, say, 30kts then the following aircraft is also moving across the ground 30kts slower than it would be in still air (for a given TAS).
If you take the moving air mass as your frame of reference, then nothing in the sky has changed. The only difference is in the rate at which the whole system (air mass, aircraft, vortex) is moving across the ground.
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Thanks Gonzo.
No problem with that if the LIDAR data shows earlier disipation.
Dave, I'm worried I'm being a bit thick here but my point is for a given TAS down final, the time to reach the same point in the air will be the same, won't it???
The vortex is travelling towards the following aircraft (relative to the ground) at whatever the headwind is (notwithstanding its disipation as Gonzo points out). Right
So if NATS propose to reduce to say 3.5NM between 2 Heavies in a 30 kt headwind to maintain a time over the threshold of around 95 seconds (equivalent to 4NM in still air), I would expect the following aircraft to hit the wake vortex in about 83 seconds (3.5NM in still air).
Please tell me I'm wrong. (But I'll keep arguing
)
No problem with that if the LIDAR data shows earlier disipation.
for a given spacing, the following aircraft would take longer to reach the preceding aircraft's vortex in a stronger headwind
The vortex is travelling towards the following aircraft (relative to the ground) at whatever the headwind is (notwithstanding its disipation as Gonzo points out). Right
So if NATS propose to reduce to say 3.5NM between 2 Heavies in a 30 kt headwind to maintain a time over the threshold of around 95 seconds (equivalent to 4NM in still air), I would expect the following aircraft to hit the wake vortex in about 83 seconds (3.5NM in still air).
Please tell me I'm wrong. (But I'll keep arguing
)
Please tell me I'm wrong.
I'd been dividing the aircraft-to-wake distance by GS instead of TAS. What I should have said was
for a given spacing, the following aircraft would take the same time to reach the preceding aircraft's vortex regardless of any headwind
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Phew. Thanks Dave.
Certainly, I think the idea has merit if its because of the earlier dissipation. No issue with that. We are working with our Met provider as well to try to analyse that behaviour.
But in their TBS video, NATS seem to be implying that they will keep "protecting" aircraft from wake turbulence because they will keep the time between arrivals over the threshold at not less than what the distance standard equates to in still air.
That is plainly incorrect.
In my experience in many aspects of aviation, this "ground centric" approach to things often causes misconception. Its often because we have trouble visualizing the medium the aircraft are flying in. If it were two boats coming up the Solent running at full tilt, its easy to see what is happening.
Certainly, I think the idea has merit if its because of the earlier dissipation. No issue with that. We are working with our Met provider as well to try to analyse that behaviour.
But in their TBS video, NATS seem to be implying that they will keep "protecting" aircraft from wake turbulence because they will keep the time between arrivals over the threshold at not less than what the distance standard equates to in still air.
That is plainly incorrect.
In my experience in many aspects of aviation, this "ground centric" approach to things often causes misconception. Its often because we have trouble visualizing the medium the aircraft are flying in. If it were two boats coming up the Solent running at full tilt, its easy to see what is happening.
Last edited by bekolblockage; 20th Feb 2014 at 12:08. Reason: can't spell
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Hi DaveReid... you quote...
If you take the moving air mass as your frame of reference, then nothing in the sky has changed. The only difference is in the rate at which the whole system (air mass, aircraft, vortex) is moving across the ground.
That would be true if all aircraft were flying en-route, but here the aircraft are constrained to the actual 3 degree glide-slope, (electronically generated line in the sky.) which is fixed w.r.t. the ground. i.e. each aircraft has a different bit of fresh air to fly down the slope.
At 10 kts windspeed the vortex moves backwards 1500ft, but only 78 ft down from the previous planes vortex trail.
Calcs.. 10kts=1000ft/min separation =1.5min therefore 1500ft horizontaly. wrt 3deg slope 1500 x tan 3 = 78ft verticaly.
If you take the moving air mass as your frame of reference, then nothing in the sky has changed. The only difference is in the rate at which the whole system (air mass, aircraft, vortex) is moving across the ground.
That would be true if all aircraft were flying en-route, but here the aircraft are constrained to the actual 3 degree glide-slope, (electronically generated line in the sky.) which is fixed w.r.t. the ground. i.e. each aircraft has a different bit of fresh air to fly down the slope.
At 10 kts windspeed the vortex moves backwards 1500ft, but only 78 ft down from the previous planes vortex trail.
Calcs.. 10kts=1000ft/min separation =1.5min therefore 1500ft horizontaly. wrt 3deg slope 1500 x tan 3 = 78ft verticaly.
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phiggs
I think it might be clutching at straws now to factor in the GS angle, but let me throw you a curve ball, just for the sake of discussion, by asking what you consider the logical extension of that idea is as the headwind increases.
Is it true to say that the effective descent angle through the air continues to reduce as the the headwind increases?
Indeed taking it to the logical extreme, if the headwind were the same as the TAS, say 150 kts, the aircraft would have to fly straight and level to maintain the G/S. No? Albeit making no forward progress.
Is it true to say that the effective descent angle through the air continues to reduce as the the headwind increases?
Indeed taking it to the logical extreme, if the headwind were the same as the TAS, say 150 kts, the aircraft would have to fly straight and level to maintain the G/S. No? Albeit making no forward progress.
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Hi Bekol...
if the headwind were the same as the TAS, say 150 kts, the aircraft would have to fly straight and level to maintain the G/S. No? Albeit making no forward progress.
Quite true, and it happens at much lower airspeed with gliders and model aircraft.... In the above example a 4nm spacing would result in zero aircraft landing per hour, they would all be fixed in space over the glide slope.
Seems strange that this topic has become one of wake turbulence separation... Surely the reason to have TBS, Time Based Separation, is to ensure a constant stream of aircraft and passengers into the airport, at a constant rate, regardless of winds.
if the headwind were the same as the TAS, say 150 kts, the aircraft would have to fly straight and level to maintain the G/S. No? Albeit making no forward progress.
Quite true, and it happens at much lower airspeed with gliders and model aircraft.... In the above example a 4nm spacing would result in zero aircraft landing per hour, they would all be fixed in space over the glide slope.
Seems strange that this topic has become one of wake turbulence separation... Surely the reason to have TBS, Time Based Separation, is to ensure a constant stream of aircraft and passengers into the airport, at a constant rate, regardless of winds.
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Phiggs
Errr, well I think thats what their main objective is with TBS- to minimize the impact of distance-based WT standards by converting to an equivalent time.
The issue for me was the reference point for that time. It should be the air, not a point on the ground. In which case, the headwind is inconsequential.
(Apart from the apparently higher dissipation rate, as pointed out by Gonzo. )
Errr, well I think thats what their main objective is with TBS- to minimize the impact of distance-based WT standards by converting to an equivalent time.
The issue for me was the reference point for that time. It should be the air, not a point on the ground. In which case, the headwind is inconsequential.
(Apart from the apparently higher dissipation rate, as pointed out by Gonzo. )
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Be interested to see this working in real life and not in the simulator which is not exactly very good at replication.
The problem I see is not the spacing on final approach, but the vectoring required when positioning aircraft in strong winds from north and south of the landing runway at the same time. I'd be surprised if you didn't have a lot more losses of separation at the point of turning onto final.
To get the aircraft the correct time based distance behind each other on final will require very tight spacing on the final turn in.
Still to be convinced I'm afraid. Looks good on paper but I know a few very experienced Heathrow radar controllers who are quite wary of the mechanics behind the procedure
The problem I see is not the spacing on final approach, but the vectoring required when positioning aircraft in strong winds from north and south of the landing runway at the same time. I'd be surprised if you didn't have a lot more losses of separation at the point of turning onto final.
To get the aircraft the correct time based distance behind each other on final will require very tight spacing on the final turn in.
Still to be convinced I'm afraid. Looks good on paper but I know a few very experienced Heathrow radar controllers who are quite wary of the mechanics behind the procedure
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The scenario to consider is that a landing aircraft might blow a tyre. The resulting go-arounds could produce a complex multiplicity of separation losses almost immediately. It will be interesting to see exactly how far the regulatory bodies will go in reducing radar separation minima without requiring much more accurate and precise data refresh for the controllers and their tools. Don't our ATC colleagues across the pond already have such equipment?
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I must say I'm impressed with the moving timing markers down final Gonzo.
Are they following the sequence according to AMAN to get the different spacing for HH and HM pairs? What happens if the INTs change the order from that in AMAN?
Did your own software guys do that on the system or the manufacturer? What system are u running for TC?
Are they following the sequence according to AMAN to get the different spacing for HH and HM pairs? What happens if the INTs change the order from that in AMAN?
Did your own software guys do that on the system or the manufacturer? What system are u running for TC?
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Gonzo:
Presumably if you get it wrong, the following aircraft comes a CROPper?
Nice to know I can still handle some physics though
There is a partner to TBS in terms of concept, called CROPS, or Crosswind Operations, which works on that very idea.
Nice to know I can still handle some physics though
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Bekol,
It's a bit old now, but this may answer a couple of your queries. Usual fees apply!
http://www.eurocontrol.int/eec/galle...eparations.pdf
It's a bit old now, but this may answer a couple of your queries. Usual fees apply!
http://www.eurocontrol.int/eec/galle...eparations.pdf
And some more pretty pictures of the TBS Demonstrator here
http://www.eurocontrol.fr/projects/e..._UserGuide.pdf
including a reference to three alternative algorithms that the simulation was able to use to compute the TTP vectors.
http://www.eurocontrol.fr/projects/e..._UserGuide.pdf
including a reference to three alternative algorithms that the simulation was able to use to compute the TTP vectors.
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I wouldn't read too much into that DR, it's a java based TBS demo to run on eDEP, rather than an actual tool.
The SESAR concept has matured significantly since 2009.
The SESAR concept has matured significantly since 2009.
